GNU troff
*********

This manual documents GNU troff version 1.22.4.

Copyright © 1994--2018 Free Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover texts being ``A GNU Manual,'' and with the Back-Cover Texts as in (a) below.  A copy of the license is included in the section entitled ``GNU Free Documentation License.''

     (a) The FSF's Back-Cover Text is: ``You have the freedom to copy and modify this GNU manual.  Buying copies from the FSF supports it in developing GNU and promoting software freedom.''

Introduction
************

GNU troff (or groff) is a system for typesetting documents.  troff is very flexible and has been used extensively for some thirty years.  It is well entrenched in the Unix community.

What Is groff?
==============

groff belongs to an older generation of document preparation systems, which operate more like compilers than the more recent interactive WYSIWYG (What You See Is What You Get) systems.  groff and its contemporary counterpart, TeX, both work using a batch paradigm: The input (or source) files are normal text files with embedded formatting commands.  These files can then be processed by groff to produce a typeset document on a variety of devices.

groff should not be confused with a word processor, an integrated system of editor and text formatter.  Also, many word processors follow the WYSIWYG paradigm discussed earlier.

Although WYSIWYG systems may be easier to use, they have a number of disadvantages compared to troff:

  * They must be used on a graphics display to work on a document.

  * Most of the WYSIWYG systems are either non-free or are not very portable.

  * troff is firmly entrenched in all Unix systems.

  * It is difficult to have a wide range of capabilities within the confines of a GUI/window system.

  * It is more difficult to make global changes to a document.

     ``GUIs normally make it simple to accomplish simple actions and impossible to accomplish complex actions.''  --Doug Gwyn (22/Jun/91 in comp.unix.wizards)

History
=======

troff can trace its origins back to a formatting program called RUNOFF, written by Jerry Saltzer, which ran on the CTSS (Compatible Time Sharing System, a project of MIT, the Massachusetts Institute of Technology) in the mid-sixties. (Jerome H. Saltzer, a grad student then, later a Professor of Electrical Engineering, now retired.  Saltzer's PhD thesis was the first application for RUNOFF and is available from the MIT Libraries.)  The name came from the use of the phrase ``run off a document'', meaning to print it out. Bob Morris ported it to the 635 architecture and called the program roff (an abbreviation of runoff).  It was rewritten as rf for the PDP-7 (before having Unix), and at the same time (1969), Doug McIlroy rewrote an extended and simplified version of roff in the BCPL programming language.

In 1971, the Unix developers wanted to get a PDP-11, and to justify the cost, proposed the development of a document formatting system for the AT&T patents division.  This first formatting program was a reimplementation of McIlroy's roff, written by J. F. Ossanna.

When they needed a more flexible language, a new version of roff called nroff (``Newer roff'') was written.  It had a much more complicated syntax, but provided the basis for all future versions. When they got a Graphic Systems CAT Phototypesetter, Ossanna wrote a version of nroff that would drive it.  It was dubbed troff, for ``typesetter roff'', although many people have speculated that it actually means ``Times roff'' because of the use of the Times font family in troff by default.  As such, the name troff is pronounced `t-roff' rather than `trough'.

With troff came nroff (they were actually the same program except for some #ifdefs), which was for producing output for line printers and character terminals.  It understood everything troff did, and ignored the commands that were not applicable (e.g. font changes).

Since there are several things that cannot be done easily in troff, work on several preprocessors began.  These programs would transform certain parts of a document into troff, which made a very natural use of pipes in Unix.

The eqn preprocessor allowed mathematical formulae to be specified in a much simpler and more intuitive manner.  tbl is a preprocessor for formatting tables.  The refer preprocessor (and the similar program, bib) processes citations in a document according to a bibliographic database.

Unfortunately, Ossanna's troff was written in PDP-11 assembly language and produced output specifically for the CAT phototypesetter. He rewrote it in C, although it was now 7000 lines of uncommented code and still dependent on the CAT.  As the CAT became less common, and was no longer supported by the manufacturer, the need to make it support other devices became a priority.  However, before this could be done, Ossanna died by a severe heart attack in a hospital while recovering from a previous one.

So, Brian Kernighan took on the task of rewriting troff.  The newly rewritten version produced device independent code that was very easy for postprocessors to read and translate to the appropriate printer codes.  Also, this new version of troff (called ditroff for ``device independent troff'') had several extensions, which included drawing functions.

Due to the additional abilities of the new version of troff, several new preprocessors appeared.  The pic preprocessor provides a wide range of drawing functions.  Likewise the ideal preprocessor did the same, although via a much different paradigm.  The grap preprocessor took specifications for graphs, but, unlike other preprocessors, produced pic code.

James Clark began work on a GNU implementation of ditroff in early 1989.  The first version, groff 0.3.1, was released June 1990.  groff included:

  * A replacement for ditroff with many extensions.

  * The soelim, pic, tbl, and eqn preprocessors.

  * Postprocessors for character devices, POSTSCRIPT, TeX DVI, and X Windows.  GNU troff also eliminated the need for a separate nroff program with a postprocessor that would produce ASCII output.

  * A version of the me macros and an implementation of the man macros.

Also, a front-end was included that could construct the, sometimes painfully long, pipelines required for all the post- and preprocessors.

Development of GNU troff progressed rapidly, and saw the additions of a replacement for refer, an implementation of the ms and mm macros, and a program to deduce how to format a document (grog).

It was declared a stable (i.e. non-beta) package with the release of version 1.04 around November 1991.

Beginning in 1999, groff has new maintainers (the package was an orphan for a few years).  As a result, new features and programs like grn, a preprocessor for gremlin images, and an output device to produce HTML and XHTML have been added.

groff Capabilities
==================

So what exactly is groff capable of doing?  groff provides a wide range of low-level text formatting operations.  Using these, it is possible to perform a wide range of formatting tasks, such as footnotes, table of contents, multiple columns, etc.  Here's a list of the most important operations supported by groff:

  * text filling, adjusting, and centering

  * hyphenation

  * page control

  * font and glyph size control

  * vertical spacing (e.g. double-spacing)

  * line length and indenting

  * macros, strings, diversions, and traps

  * number registers

  * tabs, leaders, and fields

  * input and output conventions and character translation

  * overstrike, bracket, line drawing, and zero-width functions

  * local horizontal and vertical motions and the width function

  * three-part titles

  * output line numbering

  * conditional acceptance of input

  * environment switching

  * insertions from the standard input

  * input/output file switching

  * output and error messages

Macro Packages
==============

Since groff provides such low-level facilities, it can be quite difficult to use by itself.  However, groff provides a macro facility to specify how certain routine operations (e.g. starting paragraphs, printing headers and footers, etc.) should be done.  These macros can be collected together into a macro package.  There are a number of macro packages available; the most common (and the ones described in this manual) are man, mdoc, me, ms, and mm.

Preprocessors
=============

Although groff provides most functions needed to format a document, some operations would be unwieldy (e.g. to draw pictures). Therefore, programs called preprocessors were written that understand their own language and produce the necessary groff operations.  These preprocessors are able to differentiate their own input from the rest of the document via markers.

To use a preprocessor, Unix pipes are used to feed the output from the preprocessor into groff.  Any number of preprocessors may be used on a given document; in this case, the preprocessors are linked together into one pipeline.  However, with groff, the user does not need to construct the pipe, but only tell groff what preprocessors to use.

groff currently has preprocessors for producing tables (tbl), typesetting equations (eqn), drawing pictures (pic and grn), processing bibliographies (refer), and drawing chemical structures (chem).  An associated program that is useful when dealing with preprocessors is soelim.

A free implementation of grap, a preprocessor for drawing graphs, can be obtained as an extra package; groff can use grap also.

Unique to groff is the preconv preprocessor that enables groff to handle documents in various input encodings.

There are other preprocessors in existence, but, unfortunately, no free implementations are available.  Among them is a preprocessor for drawing mathematical pictures (ideal).

Output Devices
==============

groff actually produces device independent code that may be fed into a postprocessor to produce output for a particular device. Currently, groff has postprocessors for POSTSCRIPT devices, character terminals, X Windows (for previewing), TeX DVI format, HP LaserJet 4 and Canon LBP printers (which use CAPSL), HTML, XHTML, and PDF.

Credits
=======

Large portions of this manual were taken from existing documents, most notably, the manual pages for the groff package by James Clark, and Eric Allman's papers on the me macro package.

The section on the man macro package is partly based on Susan G. Kleinmann's groff_man manual page written for the Debian GNU/Linux system.

Larry Kollar contributed the section on the ms macro package.

Invoking groff
**************

This section focuses on how to invoke the groff front end.  This front end takes care of the details of constructing the pipeline among the preprocessors, gtroff and the postprocessor.

It has become a tradition that GNU programs get the prefix g to distinguish it from its original counterparts provided by the host (see Environment, for more details).  Thus, for example, geqn is GNU eqn.  On operating systems like GNU/Linux or the Hurd, which don't contain proprietary versions of troff, and on MS-DOS/MS-Windows, where troff and associated programs are not available at all, this prefix is omitted since GNU troff is the only used incarnation of troff.  Exception: groff is never replaced by roff.

In this document, we consequently say gtroff when talking about the GNU troff program.  All other implementations of troff are called AT&T troff, which is the common origin of all troff derivates (with more or less compatible changes). Similarly, we say gpic, geqn, etc.

Options
=======

groff normally runs the gtroff program and a postprocessor appropriate for the selected device.  The default device is ps (but it can be changed when groff is configured and built).  It can optionally preprocess with any of gpic, geqn, gtbl, ggrn, grap, gchem, grefer, gsoelim, or preconv.

This section only documents options to the groff front end.  Many of the arguments to groff are passed on to gtroff, therefore those are also included.  Arguments to pre- or postprocessors can be found in Invoking gpic, Invoking geqn, Invoking gtbl, Invoking ggrn, Invoking grefer, Invoking gchem, Invoking gsoelim, Invoking preconv, Invoking grotty, Invoking grops, Invoking gropdf, Invoking grohtml, Invoking grodvi, Invoking grolj4, Invoking grolbp, and Invoking gxditview.

The command-line format for groff is:

     groff [ -abceghijklpstvzCEGNRSUVXZ ] [ -dCS ] [ -DARG ]
           [ -fFAM ] [ -FDIR ] [ -IDIR ] [ -KARG ]
           [ -LARG ] [ -mNAME ] [ -MDIR ] [ -nNUM ]
           [ -oLIST ] [ -PARG ] [ -rCN ] [ -TDEV ]
           [ -wNAME ] [ -WNAME ] [ FILES... ]

The command-line format for gtroff is as follows.

     gtroff [ -abcivzCERU ] [ -dCS ] [ -fFAM ] [ -FDIR ]
            [ -mNAME ] [ -MDIR ] [ -nNUM ] [ -oLIST ]
            [ -rCN ] [ -TNAME ] [ -wNAME ] [ -WNAME ]
            [ FILES... ]

Obviously, many of the options to groff are actually passed on to gtroff.

Options without an argument can be grouped behind a single -.  A filename of - denotes the standard input.  It is possible to have whitespace between an option and its parameter.

The grog command can be used to guess the correct groff command to format a file.

Here's the description of the command-line options:

-a
     Generate an ASCII approximation of the typeset output.  The read-only register .A is then set to 1.  See Built-in Registers.  A typical example is

          groff -a -man -Tdvi troff.man | less

     which shows how lines are broken for the DVI device.  Note that this option is rather useless today since graphic output devices are available virtually everywhere.

-b
     Print a backtrace with each warning or error message.  This backtrace should help track down the cause of the error.  The line numbers given in the backtrace may not always be correct: gtroff can get confused by as or am requests while counting line numbers.

-c
     Suppress color output.

-C
     Enable compatibility mode.  See Implementation Differences, for the list of incompatibilities between groff and AT&T troff.

-dCS
-dNAME=S
     Define C or NAME to be a string S. C must be a one-letter name; NAME can be of arbitrary length.  All string assignments happen before loading any macro file (including the start-up file).

-DARG
     Set default input encoding used by preconv to ARG.  Implies -k.

-e
     Preprocess with geqn.

-E
     Inhibit all error messages.

-fFAM
     Use FAM as the default font family.  See Font Families.

-FDIR
     Search DIR for subdirectories devNAME (NAME is the name of the device), for the DESC file, and for font files before looking in the standard directories (see Font Directories).  This option is passed to all pre- and postprocessors using the GROFF_FONT_PATH environment variable.

-g
     Preprocess with ggrn.

-G
     Preprocess with grap.  Implies -p.

-h
     Print a help message.

-i
     Read the standard input after all the named input files have been processed.

-IDIR
     This option may be used to specify a directory to search for files. It is passed to the following programs:

       * gsoelim (see gsoelim for more details); it also implies groff's -s option.

       * gtroff; it is used to search files named in the psbb and so requests.

       * grops; it is used to search files named in the \X'ps: import and \X'ps: file escapes.

     The current directory is always searched first.  This option may be specified more than once; the directories are searched in the order specified.  No directory search is performed for files specified using an absolute path.

-j
     Preprocess with gchem.  Implies -p.

-k
     Preprocess with preconv.  This is run before any other preprocessor.  Please refer to preconv's manual page for its behaviour if no -K (or -D) option is specified.

-KARG
     Set input encoding used by preconv to ARG.  Implies -k.

-l
     Send the output to a spooler for printing.  The command used for this is specified by the print command in the device description file (see Font Files, for more info).  If not present, -l is ignored.

-LARG
     Pass ARG to the spooler.  Each argument should be passed with a separate -L option.  Note that groff does not prepend a - to ARG before passing it to the postprocessor.  If the print keyword in the device description file is missing, -L is ignored.

-mNAME
     Read in the file NAME.tmac.  Normally groff searches for this in its macro directories.  If it isn't found, it tries tmac.NAME (searching in the same directories).

-MDIR
     Search directory DIR for macro files before the standard directories (see Macro Directories).

-nNUM
     Number the first page NUM.

-N
     Don't allow newlines with eqn delimiters.  This is the same as the -N option in geqn.

-oLIST
     Output only pages in LIST, which is a comma-separated list of page ranges; N means print page N, M-N means print every page between M and N, -N means print every page up to N, N- means print every page beginning with N.  gtroff exits after printing the last page in the list.  All the ranges are inclusive on both ends.

     Within gtroff, this information can be extracted with the .P register.  See Built-in Registers.

     If your document restarts page numbering at the beginning of each chapter, then gtroff prints the specified page range for each chapter.

-p
     Preprocess with gpic.

-PARG
     Pass ARG to the postprocessor.  Each argument should be passed with a separate -P option.  Note that groff does not prepend - to ARG before passing it to the postprocessor.

-rCN
-rNAME=N
     Set number register C or NAME to the value N.  C must be a one-letter name; NAME can be of arbitrary length.  N can be any gtroff numeric expression.  All register assignments happen before loading any macro file (including the start-up file).

-R
     Preprocess with grefer.  No mechanism is provided for passing arguments to grefer because most grefer options have equivalent commands that can be included in the file.  See grefer, for more details.

     Note that gtroff also accepts a -R option, which is not accessible via groff.  This option prevents the loading of the troffrc and troffrc-end files.

-s
     Preprocess with gsoelim.

-S
     Safer mode.  Pass the -S option to gpic and disable the open, opena, pso, sy, and pi requests.  For security reasons, this is enabled by default.

-t
     Preprocess with gtbl.

-TDEV
     Prepare output for device DEV.  The default device is ps, unless changed when groff was configured and built.  The following are the output devices currently available:

     ps
          For POSTSCRIPT printers and previewers.

     pdf
          For PDF viewers or printers.

     dvi
          For TeX DVI format.

     X75
          For a 75dpi X11 previewer.

     X75-12
          For a 75dpi X11 previewer with a 12pt base font in the document.

     X100
          For a 100dpi X11 previewer.

     X100-12
          For a 100dpi X11 previewer with a 12pt base font in the document.

     ascii
          For typewriter-like devices using the (7-bit) ASCII character set.

     latin1
          For typewriter-like devices that support the Latin-1 (ISO 8859-1) character set.

     utf8
          For typewriter-like devices that use the Unicode (ISO 10646) character set with UTF-8 encoding.

     cp1047
          For typewriter-like devices that use the EBCDIC encoding IBM cp1047.

     lj4
          For HP LaserJet4-compatible (or other PCL5-compatible) printers.

     lbp
          For Canon CAPSL printers (LBP-4 and LBP-8 series laser printers).

     html
     xhtml
          To produce HTML and XHTML output, respectively. Note that this driver consists of two parts, a preprocessor (pre-grohtml) and a postprocessor (post-grohtml).

     The predefined gtroff string register .T contains the current output device; the read-only number register .T is set to 1 if this option is used (which is always true if groff is used to call gtroff).  See Built-in Registers.

     The postprocessor to be used for a device is specified by the postpro command in the device description file.  (see Font Files, for more info.)  This can be overridden with the -X option.

-U
     Unsafe mode.  This enables the open, opena, pso, sy, and pi requests.

-wNAME
     Enable warning NAME.  Available warnings are described in Debugging.  Multiple -w options are allowed.

-WNAME
     Inhibit warning NAME.  Multiple -W options are allowed.

-v
     Make programs run by groff print out their version number.

-V
     Print the pipeline on stdout instead of executing it.  If specified more than once, print the pipeline on stderr and execute it.

-X
     Preview with gxditview instead of using the usual postprocessor. This is unlikely to produce good results except with -Tps.

     Note that this is not the same as using -TX75 or -TX100 to view a document with gxditview: The former uses the metrics of the specified device, whereas the latter uses X-specific fonts and metrics.

-z
     Suppress output from gtroff.  Only error messages are printed.

-Z
     Do not postprocess the output of gtroff.  Normally groff automatically runs the appropriate postprocessor.

Environment
===========

There are also several environment variables (of the operating system, not within gtroff) that can modify the behavior of groff.

GROFF_BIN_PATH
     This search path, followed by PATH, is used for commands executed by groff.

GROFF_COMMAND_PREFIX
     If this is set to X, then groff runs Xtroff instead of gtroff.  This also applies to tbl, pic, eqn, grn, chem, refer, and soelim.  It does not apply to grops, grodvi, grotty, pre-grohtml, post-grohtml, preconv, grolj4, gropdf, and gxditview.

     The default command prefix is determined during the installation process.  If a non-GNU troff system is found, prefix g is used, none otherwise.

GROFF_ENCODING
     The value of this environment value is passed to the preconv preprocessor to select the encoding of input files.  Setting this option implies groff's command-line option -k (that is, groff actually always calls preconv).  If set without a value, groff calls preconv without arguments.  An explicit -K command-line option overrides the value of GROFF_ENCODING.  See the manual page of preconv for details.

GROFF_FONT_PATH
     A colon-separated list of directories in which to search for the devNAME directory (before the default directories are tried).  See Font Directories.

GROFF_TMAC_PATH
     A colon-separated list of directories in which to search for macro files (before the default directories are tried).  See Macro Directories.

GROFF_TMPDIR
     The directory in which groff creates temporary files.  If this is not set and TMPDIR is set, temporary files are created in that directory.  Otherwise temporary files are created in a system-dependent default directory (on Unix and GNU/Linux systems, this is usually /tmp).  grops, grefer, pre-grohtml, and post-grohtml can create temporary files in this directory.

GROFF_TYPESETTER
     The default output device.

SOURCE_DATE_EPOCH
     A timestamp (expressed as seconds since the Unix epoch) to use in place of the current time when initializing time-based built-in registers such as \n[seconds].

Note that MS-DOS and MS-Windows ports of groff use semi-colons, rather than colons, to separate the directories in the lists described above.

Macro Directories
=================

All macro file names must be named NAME.tmac or tmac.NAME to make the -mNAME command-line option work.  The mso request doesn't have this restriction; any file name can be used, and gtroff won't try to append or prepend the tmac string.

Macro files are kept in the tmac directories, all of which constitute the tmac path.  The elements of the search path for macro files are (in that order):

  * The directories specified with gtroff's or groff's -M command-line option.

  * The directories given in the GROFF_TMAC_PATH environment variable.

  * The current directory (only if in unsafe mode using the -U command-line switch).

  * The home directory.

  * A platform-dependent directory, a site-specific (platform-independent) directory, and the main tmac directory; the default locations are

          /usr/local/lib/groff/site-tmac
          /usr/local/share/groff/site-tmac
          /usr/local/share/groff/1.22.3/tmac

     assuming that the version of groff is 1.22.3, and the installation prefix was /usr/local.  It is possible to fine-tune those directories during the installation process.

Font Directories
================

Basically, there is no restriction how font files for groff are named and how long font names are; however, to make the font family mechanism work (see Font Families), fonts within a family should start with the family name, followed by the shape.  For example, the Times family uses T for the family name and R, B, I, and BI to indicate the shapes `roman', `bold', `italic', and `bold italic', respectively.  Thus the final font names are TR, TB, TI, and TBI.

All font files are kept in the font directories, which constitute the font path.  The file search functions always append the directory devNAME, where NAME is the name of the output device.  Assuming, say, DVI output, and /foo/bar as a font directory, the font files for grodvi must be in /foo/bar/devdvi.

The elements of the search path for font files are (in that order):

  * The directories specified with gtroff's or groff's -F command-line option.  All device drivers and some preprocessors also have this option.

  * The directories given in the GROFF_FONT_PATH environment variable.

  * A site-specific directory and the main font directory; the default locations are

          /usr/local/share/groff/site-font
          /usr/local/share/groff/1.22.3/font

     assuming that the version of groff is 1.22.3, and the installation prefix was /usr/local.  It is possible to fine-tune those directories during the installation process.

Paper Size
==========

In groff, the page size for gtroff and for output devices are handled separately.  See Page Layout, for vertical manipulation of the page size.  See Line Layout, for horizontal changes.

A default paper size can be set in the device's DESC file.  Most output devices also have a command-line option -p to override the default paper size and option -l to use landscape orientation.  See DESC File Format, for a description of the papersize keyword, which takes the same argument as -p.

A convenient shorthand to set a particular paper size for gtroff is command-line option -dpaper=SIZE.  This defines string paper, which is processed in file papersize.tmac (loaded in the start-up file troffrc by default).  Possible values for SIZE are the same as the predefined values for the papersize keyword (but only in lowercase) except a7--d7.  An appended l (ell) character denotes landscape orientation.

For example, use the following for PS output on A4 paper in landscape orientation:

     groff -Tps -dpaper=a4l -P-pa4 -P-l -ms foo.ms > foo.ps

Note that it is up to the particular macro package to respect default page dimensions set in this way (most do).

Invocation Examples
===================

This section lists several common uses of groff and the corresponding command lines.

     groff file

This command processes file without a macro package or a preprocessor.  The output device is the default, ps, and the output is sent to stdout.

     groff -t -mandoc -Tascii file | less

This is basically what a call to the man program does. gtroff processes the manual page file with the mandoc macro file (which in turn either calls the man or the mdoc macro package), using the tbl preprocessor and the ASCII output device.  Finally, the less pager displays the result.

     groff -X -m me file

Preview file with gxditview, using the me macro package.  Since no -T option is specified, use the default device (ps).  Note that you can either say -m me or -me; the latter is an anachronism from the early days of Unix. (The same is true for the other main macro packages that come with groff: man, mdoc, ms, mm, and mandoc.  This won't work in general; for example, to load trace.tmac, either -mtrace or -m trace must be used.)

     groff -man -rD1 -z file

Check file with the man macro package, forcing double-sided printing -- don't produce any output.

grog
----

grog reads files, guesses which of the groff preprocessors and/or macro packages are required for formatting them, and prints the groff command including those options on the standard output.  It generates one or more of the options -e, -man, -me, -mm, -mom, -ms, -mdoc, -mdoc-old, -p, -R, -g, -G, -s, and -t.

A special file name - refers to the standard input. Specifying no files also means to read the standard input.  Any specified options are included in the printed command.  No space is allowed between options and their arguments.  The only options recognized are -C (which is also passed on) to enable compatibility mode, and -v to print the version number and exit.

For example,

     grog -Tdvi paper.ms

guesses the appropriate command to print paper.ms and then prints it to the command line after adding the -Tdvi option.  For direct execution, enclose the call to grog in backquotes at the Unix shell prompt:

     `grog -Tdvi paper.ms` > paper.dvi

As seen in the example, it is still necessary to redirect the output to something meaningful (i.e. either a file or a pager program like less).

Tutorial for Macro Users
************************

Most users tend to use a macro package to format their papers.  This means that the whole breadth of groff is not necessary for most people.  This chapter covers the material needed to efficiently use a macro package.

Basics
======

This section covers some of the basic concepts necessary to understand how to use a macro package. (This section is derived from Writing Papers with nroff using -me by Eric P. Allman.) References are made throughout to more detailed information, if desired.

gtroff reads an input file prepared by the user and outputs a formatted document suitable for publication or framing.  The input consists of text, or words to be printed, and embedded commands (requests and escapes), which tell gtroff how to format the output.  For more detail on this, see Embedded Commands.

The word argument is used in this chapter to mean a word or number that appears on the same line as a request, and which modifies the meaning of that request.  For example, the request

     .sp

spaces one line, but

     .sp 4

spaces four lines.  The number 4 is an argument to the sp request, which says to space four lines instead of one.  Arguments are separated from the request and from each other by spaces (no tabs).  More details on this can be found in Request and Macro Arguments.

The primary function of gtroff is to collect words from input lines, fill output lines with those words, justify the right-hand margin by inserting extra spaces in the line, and output the result.  For example, the input:

     Now is the time
     for all good men
     to come to the aid
     of their party.
     Four score and seven
     years ago, etc.

is read, packed onto output lines, and justified to produce:

     Now is the time for all good men to come to the aid of their party. Four score and seven years ago, etc.

Sometimes a new output line should be started even though the current line is not yet full; for example, at the end of a paragraph.  To do this it is possible to cause a break, which starts a new output line.  Some requests cause a break automatically, as normally do blank input lines and input lines beginning with a space.

Not all input lines are text to be formatted.  Some input lines are requests that describe how to format the text.  Requests always have a period (.) or an apostrophe (') as the first character of the input line.

The text formatter also does more complex things, such as automatically numbering pages, skipping over page boundaries, putting footnotes in the correct place, and so forth.

Here are a few hints for preparing text for input to gtroff.

  * First, keep the input lines short.  Short input lines are easier to edit, and gtroff packs words onto longer lines anyhow.

  * In keeping with this, it is helpful to begin a new line after every comma or phrase, since common corrections are to add or delete sentences or phrases.

  * End each sentence with two spaces -- or better, start each sentence on a new line.  gtroff recognizes characters that usually end a sentence, and inserts sentence space accordingly.

  * Do not hyphenate words at the end of lines -- gtroff is smart enough to hyphenate words as needed, but is not smart enough to take hyphens out and join a word back together.  Also, words such as ``mother-in-law'' should not be broken over a line, since then a space can occur where not wanted, such as ``mother- in-law''.

gtroff double-spaces output text automatically if you use the request .ls 2.  Reactivate single-spaced mode by typing .ls 1. (If you need finer granularity of the vertical space, use the pvs request (see Changing Type Sizes).)

A number of requests allow to change the way the output looks, sometimes called the layout of the output page.  Most of these requests adjust the placing of whitespace (blank lines or spaces).

The bp request starts a new page, causing a line break.

The request .sp N leaves N lines of blank space.  N can be omitted (meaning skip a single line) or can be of the form Ni (for N inches) or Nc (for N centimeters).  For example, the input:

     .sp 1.5i
     My thoughts on the subject
     .sp

leaves one and a half inches of space, followed by the line ``My thoughts on the subject'', followed by a single blank line (more measurement units are available, see Measurements).

Text lines can be centered by using the ce request.  The line after ce is centered (horizontally) on the page.  To center more than one line, use .ce N (where N is the number of lines to center), followed by the N lines.  To center many lines without counting them, type:

     .ce 1000
     lines to center
     .ce 0

The .ce 0 request tells groff to center zero more lines, in other words, stop centering.

All of these requests cause a break; that is, they always start a new line.  To start a new line without performing any other action, use br.

Common Features
===============

gtroff provides very low-level operations for formatting a document.  There are many common routine operations that are done in all documents.  These common operations are written into macros and collected into a macro package.

All macro packages provide certain common capabilities that fall into the following categories.

Paragraphs
----------

One of the most common and most used capability is starting a paragraph. There are a number of different types of paragraphs, any of which can be initiated with macros supplied by the macro package.  Normally, paragraphs start with a blank line and the first line indented, like the text in this manual.  There are also block style paragraphs, which omit the indentation:

     Some   men  look   at  constitutions   with  sanctimonious
     reverence, and deem them like the ark of the covenant, too
     sacred to be touched.

And there are also indented paragraphs, which begin with a tag or label at the margin and the remaining text indented.

     one   This is  the first paragraph.  Notice  how the first
           line of  the resulting  paragraph lines up  with the
           other lines in the paragraph.

     longlabel
           This  paragraph   had  a  long   label.   The  first
           character of text on the first line does not line up
           with  the  text  on  second  and  subsequent  lines,
           although they line up with each other.

A variation of this is a bulleted list.

     .     Bulleted lists start with a bullet.   It is possible
           to use other glyphs instead of the bullet.  In nroff
           mode using the ASCII character set for output, a dot
           is used instead of a real bullet.

Sections and Chapters
---------------------

Most macro packages supply some form of section headers.  The simplest kind is simply the heading on a line by itself in bold type.  Others supply automatically numbered section heading or different heading styles at different levels.  Some, more sophisticated, macro packages supply macros for starting chapters and appendices.

Headers and Footers
-------------------

Every macro package gives some way to manipulate the headers and footers (also called titles) on each page.  This is text put at the top and bottom of each page, respectively, which contain data like the current page number, the current chapter title, and so on.  Its appearance is not affected by the running text.  Some packages allow for different ones on the even and odd pages (for material printed in a book form).

The titles are called three-part titles, that is, there is a left-justified part, a centered part, and a right-justified part.  An automatically generated page number may be put in any of these fields with the % character (see Page Layout, for more details).

Page Layout
-----------

Most macro packages let the user specify top and bottom margins and other details about the appearance of the printed pages.

Displays
--------

Displays are sections of text to be set off from the body of the paper.  Major quotes, tables, and figures are types of displays, as are all the examples used in this document.

Major quotes are quotes that are several lines long, and hence are set in from the rest of the text without quote marks around them.

A list is an indented, single-spaced, unfilled display.  Lists should be used when the material to be printed should not be filled and justified like normal text, such as columns of figures or the examples used in this paper.

A keep is a display of lines that are kept on a single page if possible.  An example for a keep might be a diagram.  Keeps differ from lists in that lists may be broken over a page boundary whereas keeps are not.

Floating keeps move relative to the text.  Hence, they are good for things that are referred to by name, such as ``See figure 3''. A floating keep appears at the bottom of the current page if it fits; otherwise, it appears at the top of the next page.  Meanwhile, the surrounding text `flows' around the keep, thus leaving no blank areas.

Footnotes and Annotations
-------------------------

There are a number of requests to save text for later printing.

Footnotes are printed at the bottom of the current page.

Delayed text is very similar to a footnote except that it is printed when called for explicitly.  This allows a list of references to appear (for example) at the end of each chapter, as is the convention in some disciplines.

Most macro packages that supply this functionality also supply a means of automatically numbering either type of annotation.

Table of Contents
-----------------

Tables of contents are a type of delayed text having a tag (usually the page number) attached to each entry after a row of dots. The table accumulates throughout the paper until printed, usually after the paper has ended.  Many macro packages provide the ability to have several tables of contents (e.g. a standard table of contents, a list of tables, etc).

Indices
-------

While some macro packages use the term index, none actually provide that functionality.  The facilities they call indices are actually more appropriate for tables of contents.

To produce a real index in a document, external tools like the makeindex program are necessary.

Paper Formats
-------------

Some macro packages provide stock formats for various kinds of documents.  Many of them provide a common format for the title and opening pages of a technical paper.  The mm macros in particular provide formats for letters and memoranda.

Multiple Columns
----------------

Some macro packages (but not man) provide the ability to have two or more columns on a page.

Font and Size Changes
---------------------

The built-in font and size functions are not always intuitive, so all macro packages provide macros to make these operations simpler.

Predefined Strings
------------------

Most macro packages provide various predefined strings for a variety of uses; examples are sub- and superscripts, printable dates, quotes and various special characters.

Preprocessor Support
--------------------

All macro packages provide support for various preprocessors and may extend their functionality.

For example, all macro packages mark tables (which are processed with gtbl) by placing them between TS and TE macros. The ms macro package has an option, .TS H, that prints a caption at the top of a new page (when the table is too long to fit on a single page).

Configuration and Customization
-------------------------------

Some macro packages provide means of customizing many of the details of how the package behaves.  This ranges from setting the default type size to changing the appearance of section headers.

Macro Packages
**************

This chapter documents the main macro packages that come with groff.

Different main macro packages can't be used at the same time; for example

     groff -m man foo.man -m ms bar.doc

doesn't work.  Note that option arguments are processed before non-option arguments; the above (failing) sample is thus reordered to

     groff -m man -m ms foo.man bar.doc

man
===

This is the most popular and probably the most important macro package of groff.  It is easy to use, and a vast majority of manual pages are based on it.

Options
-------

The command-line format for using the man macros with groff is:

     groff -m man [ -rLL=LENGTH ] [ -rLT=LENGTH ] [ -rFT=DIST ]
           [ -rcR=1 ] [ -rC1 ] [ -rD1 ] [-rHY=FLAGS ]
           [ -rPNNN ] [ -rSXX ] [ -rXNNN ]
           [ -rIN=LENGTH ] [ -rSN=LENGTH ] [ FILES... ]

It is possible to use -man instead of -m man.

-rcR=1
     This option (the default if a TTY output device is used) creates a single, very long page instead of multiple pages.  Use -rcR=0 to disable it.

-rC1
     If more than one manual page is given on the command line, number the pages continuously, rather than starting each at 1.

-rD1
     Double-sided printing.  Footers for even and odd pages are formatted differently.

-rFT=DIST
     Set the position of the footer text to DIST.  If positive, the distance is measured relative to the top of the page, otherwise it is relative to the bottom.  The default is -0.5i.

-rHY=FLAGS
     Set hyphenation flags.  Possible values are 1 to hyphenate without restrictions, 2 to not hyphenate the last word on a page, 4 to not hyphenate the last two characters of a word, and 8 to not hyphenate the first two characters of a word.  These values are additive; the default is 8.

-rIN=LENGTH
     Set the body text indentation to LENGTH.  If not specified, the indentation defaults to 7n (7 characters) in nroff mode and 7.2n otherwise.  For nroff, this value should always be an integer multiple of unit n to get consistent indentation.

-rLL=LENGTH
     Set line length to LENGTH.  If not specified, the line length is set to respect any value set by a prior ll request (which must be in effect when the TH macro is invoked), if this differs from the built-in default for the formatter; otherwise it defaults to 78n in nroff mode (this is 78 characters per line) and 6.5i in troff mode. (Note that the use of a .ll LENGTH request to initialize the line length, prior to use of the TH macro, is supported for backward compatibility with some versions of the man program.  Always use the -rLL=LENGTH option, or an equivalent .nr LL LENGTH request, in preference to such a .ll LENGTH request.  In particular, note that in nroff mode, the request .ll 65n, (with any LENGTH expression that evaluates equal to 65n, i.e., the formatter's default line length in nroff mode), does not set the line length to 65n (it is adjusted to the man macro package's default setting of 78n), whereas the use of the -rLL=65n option, or the .nr LL 65n request does establish a line length of 65n.)

-rLT=LENGTH
     Set title length to LENGTH.  If not specified, the title length defaults to the line length.

-rPNNN
     Page numbering starts with NNN rather than with 1.

-rSXX
     Use XX (which can be 10, 11, or 12pt) as the base document font size instead of the default value of 10pt.

-rSN=LENGTH
     Set the indentation for sub-subheadings to LENGTH.  If not specified, the indentation defaults to 3n.

-rXNNN
     After page NNN, number pages as NNNa, NNNb, NNNc, etc.  For example, the option -rX2 produces the following page numbers: 1, 2, 2a, 2b, 2c, etc.

Usage
-----

This section describes the available macros for manual pages.  For further customization, put additional macros and requests into the file man.local, which is loaded immediately after the man package.

 -- Macro: .TH, title section [extra1 [extra2 [extra3]]], man
     Set the title of the man page to TITLE and the section to SECTION, which must have a value between 1 and 8.  The value of SECTION may also have a string appended, e.g. .pm, to indicate a specific subsection of the man pages.

     Both TITLE and SECTION are positioned at the left and right in the header line (with SECTION in parentheses immediately appended to TITLE.  EXTRA1 is positioned in the middle of the footer line.  EXTRA2 is positioned at the left in the footer line (or at the left on even pages and at the right on odd pages if double-sided printing is active).  EXTRA3 is centered in the header line.

     For HTML and XHTML output, headers and footers are completely suppressed.

     Additionally, this macro starts a new page; the new line number is 1 again (except if the -rC1 option is given on the command line) -- this feature is intended only for formatting multiple man pages; a single man page should contain exactly one TH macro at the beginning of the file.

 -- Macro: .SH, [heading], man
     Set up an unnumbered section heading sticking out to the left.  Prints out all the text following SH up to the end of the line (or the text in the next line if there is no argument to SH) in bold face (or the font specified by the string HF), one size larger than the base document size.  Additionally, the left margin and the indentation for the following text is reset to its default value.

 -- Macro: .SS, [heading], man
     Set up an unnumbered (sub)section heading.  Prints out all the text following SS up to the end of the line (or the text in the next line if there is no argument to SS) in bold face (or the font specified by the string HF), at the same size as the base document size.  Additionally, the left margin and the indentation for the following text is reset to its default value.

 -- Macro: .TP, [nnn], man
     Set up an indented paragraph with label.  The indentation is set to NNN if that argument is supplied (the default unit is n if omitted), otherwise it is set to the previous indentation value specified with TP, IP, or HP (or to the default value if none of them have been used yet).

     The first line of text following this macro is interpreted as a string to be printed flush-left, as it is appropriate for a label.  It is not interpreted as part of a paragraph, so there is no attempt to fill the first line with text from the following input lines.  Nevertheless, if the label is not as wide as the indentation the paragraph starts at the same line (but indented), continuing on the following lines.  If the label is wider than the indentation the descriptive part of the paragraph begins on the line following the label, entirely indented. Note that neither font shape nor font size of the label is set to a default value; on the other hand, the rest of the text has default font settings.

 -- Macro: .LP, , man
 -- Macro: .PP, , man
 -- Macro: .P, , man
     These macros are mutual aliases.  Any of them causes a line break at the current position, followed by a vertical space downwards by the amount specified by the PD macro.  The font size and shape are reset to the default value (10pt roman if no -rS option is given on the command line).  Finally, the current left margin and the indentation is restored.

 -- Macro: .IP, [designator [nnn]], man
     Set up an indented paragraph, using DESIGNATOR as a tag to mark its beginning.  The indentation is set to NNN if that argument is supplied (default unit is n), otherwise it is set to the previous indentation value specified with TP, IP, or HP (or the default value if none of them have been used yet).  Font size and face of the paragraph (but not the designator) are reset to their default values.

     To start an indented paragraph with a particular indentation but without a designator, use "" (two double quotes) as the first argument of IP.

     For example, to start a paragraph with bullets as the designator and 4 en indentation, write

          .IP \(bu 4

 -- Macro: .HP, [nnn], man
     Set up a paragraph with hanging left indentation.  The indentation is set to NNN if that argument is supplied (default unit is n), otherwise it is set to the previous indentation value specified with TP, IP, or HP (or the default value if non of them have been used yet).  Font size and face are reset to their default values.

 -- Macro: .RS, [nnn], man
     Move the left margin to the right by the value NNN if specified (default unit is n); otherwise it is set to the previous indentation value specified with TP, IP, or HP (or to the default value if none of them have been used yet).  The indentation value is then set to the default.

     Calls to the RS macro can be nested.

 -- Macro: .RE, [nnn], man
     Move the left margin back to level NNN, restoring the previous left margin.  If no argument is given, it moves one level back.  The first level (i.e., no call to RS yet) has number 1, and each call to RS increases the level by 1.

To summarize, the following macros cause a line break with the insertion of vertical space (which amount can be changed with the PD macro): SH, SS, TP, LP (PP, P), IP, and HP.

The macros RS and RE also cause a break but do not insert vertical space.

Finally, the macros SH, SS, LP (PP, P), and RS reset the indentation to its default value.

Macros to set fonts
-------------------

The standard font is roman; the default text size is 10 points.  If command-line option -rS=N is given, use N points as the default text size.

 -- Macro: .SM, [text], man
     Set the text on the same line or the text on the next line in a font that is one point size smaller than the default font.

 -- Macro: .SB, [text], man
     Set the text on the same line or the text on the next line in bold face font, one point size smaller than the default font.

 -- Macro: .BI, text, man
     Set its arguments alternately in bold face and italic, without a space between the arguments.  Thus,

          .BI this "word and" that

     produces ``thisword andthat'' with ``this'' and ``that'' in bold face, and ``word and'' in italics.

 -- Macro: .IB, text, man
     Set its arguments alternately in italic and bold face, without a space between the arguments.

 -- Macro: .RI, text, man
     Set its arguments alternately in roman and italic, without a space between the arguments.

 -- Macro: .IR, text, man
     Set its arguments alternately in italic and roman, without a space between the arguments.

 -- Macro: .BR, text, man
     Set its arguments alternately in bold face and roman, without a space between the arguments.

 -- Macro: .RB, text, man
     Set its arguments alternately in roman and bold face, without a space between the arguments.

 -- Macro: .B, [text], man
     Set TEXT in bold face.  If no text is present on the line where the macro is called, then the text of the next line appears in bold face.

 -- Macro: .I, [text], man
     Set TEXT in italic.  If no text is present on the line where the macro is called, then the text of the next line appears in italic.

Miscellaneous macros
--------------------

The default indentation is 7.2n in troff mode and 7n in nroff mode except for grohtml, which ignores indentation.

 -- Macro: .DT, , man
     Set tabs every 0.5 inches.  Since this macro is always executed during a call to the TH macro, it makes sense to call it only if the tab positions have been changed.

 -- Macro: .PD, [nnn], man
     Adjust the empty space before a new paragraph (or section).  The optional argument gives the amount of space (default unit is v); without parameter, the value is reset to its default value (1 line in nroff mode, 0.4v otherwise).

     This affects the macros SH, SS, TP, LP (as well as PP and P), IP, and HP.

The following two macros are included for BSD compatibility.

 -- Macro: .AT, [system [release]], man
     Alter the footer for use with AT&T manpages.  This command exists only for compatibility; don't use it.  The first argument SYSTEM can be:

     3
          7th Edition (the default)

     4
          System III

     5
          System V

     An optional second argument RELEASE to AT specifies the release number (such as ``System V Release 3'').

 -- Macro: .UC, [version], man
     Alters the footer for use with BSD manpages.  This command exists only for compatibility; don't use it.  The argument can be:

     3
          3rd Berkeley Distribution (the default)

     4
          4th Berkeley Distribution

     5
          4.2 Berkeley Distribution

     6
          4.3 Berkeley Distribution

     7
          4.4 Berkeley Distribution

Predefined strings
------------------

The following strings are defined:

 -- String: \*[S, man]
     Switch back to the default font size.

 -- String: \*[HF, man]
     The typeface used for headings. The default is B.

 -- String: \*[R, man]
     The `registered' sign.

 -- String: \*[Tm, man]
     The `trademark' sign.

 -- String: \*[lq, man]
 -- String: \*[rq, man]
     Left and right quote.  This is equal to \(lq and \(rq, respectively.

Preprocessors in man pages
--------------------------

If a preprocessor like gtbl or geqn is needed, it has become common usage to make the first line of the man page look like this:

     '\" WORD

Note the single space character after the double quote.  WORD consists of letters for the needed preprocessors: e for geqn, r for grefer, t for gtbl. Modern implementations of the man program read this first line and automatically call the right preprocessor(s).

Optional man extensions
-----------------------

Use the file man.local for local extensions to the man macros or for style changes.

Custom headers and footers
..........................

In groff versions 1.18.2 and later, you can specify custom headers and footers by redefining the following macros in man.local.

 -- Macro: .PT, , man
     Control the content of the headers.  Normally, the header prints the command name and section number on either side, and the optional fifth argument to TH in the center.

 -- Macro: .BT, , man
     Control the content of the footers.  Normally, the footer prints the page number and the third and fourth arguments to TH.

     Use the FT number register to specify the footer position.  The default is -0.5i.

Ultrix-specific man macros
..........................

The groff source distribution includes a file named man.ultrix, containing macros compatible with the Ultrix variant of man.  Copy this file into man.local (or use the mso request to load it) to enable the following macros.

 -- Macro: .CT, key, man
     Print <CTRL/KEY>.

 -- Macro: .CW, , man
     Print subsequent text using the constant width (Courier) typeface.

 -- Macro: .Ds, , man
     Begin a non-filled display.

 -- Macro: .De, , man
     End a non-filled display started with Ds.

 -- Macro: .EX, [indent], man
     Begin a non-filled display using the constant width (Courier) typeface. Use the optional INDENT argument to indent the display.

 -- Macro: .EE, , man
     End a non-filled display started with EX.

 -- Macro: .G, [text], man
     Set TEXT in Helvetica.  If no text is present on the line where the macro is called, then the text of the next line appears in Helvetica.

 -- Macro: .GL, [text], man
     Set TEXT in Helvetica Oblique.  If no text is present on the line where the macro is called, then the text of the next line appears in Helvetica Oblique.

 -- Macro: .HB, [text], man
     Set TEXT in Helvetica Bold.  If no text is present on the line where the macro is called, then all text up to the next HB appears in Helvetica Bold.

 -- Macro: .TB, [text], man
     Identical to HB.

 -- Macro: .MS, title sect [punct], man
     Set a manpage reference in Ultrix format.  The TITLE is in Courier instead of italic.  Optional punctuation follows the section number without an intervening space.

 -- Macro: .NT, [C] [title], man
     Begin a note.  Print the optional title, or the word ``Note'', centered on the page.  Text following the macro makes up the body of the note, and is indented on both sides.  If the first argument is C, the body of the note is printed centered (the second argument replaces the word ``Note'' if specified).

 -- Macro: .NE, , man
     End a note begun with NT.

 -- Macro: .PN, path [punct], man
     Set the path name in constant width (Courier), followed by optional punctuation.

 -- Macro: .Pn, [punct] path [punct], man
     If called with two arguments, identical to PN.  If called with three arguments, set the second argument in constant width (Courier), bracketed by the first and third arguments in the current font.

 -- Macro: .R, , man
     Switch to roman font and turn off any underlining in effect.

 -- Macro: .RN, , man
     Print the string <RETURN>.

 -- Macro: .VS, [4], man
     Start printing a change bar in the margin if the number 4 is specified.  Otherwise, this macro does nothing.

 -- Macro: .VE, , man
     End printing the change bar begun by VS.

Simple example
..............

The following example man.local file alters the SH macro to add some extra vertical space before printing the heading.  Headings are printed in Helvetica Bold.

     .\" Make the heading fonts Helvetica
     .ds HF HB
     .
     .\" Put more whitespace in front of headings.
     .rn SH SH-orig
     .de SH
     .  if t .sp (u;\\n[PD]*2)
     .  SH-orig \\$*
     ..

mdoc
====

See the groff_mdoc(7) man page (type man groff_mdoc at the command line).

ms
==

The -ms macros are suitable for reports, letters, books, user manuals, and so forth.  The package provides macros for cover pages, section headings, paragraphs, lists, footnotes, pagination, and a table of contents.

Introduction to ms
------------------

The original -ms macros were included with AT&T troff as well as the man macros.  While the man package is intended for brief documents that can be read on-line as well as printed, the ms macros are suitable for longer documents that are meant to be printed rather than read on-line.

The ms macro package included with groff is a complete, bottom-up re-implementation.  Several macros (specific to AT&T or Berkeley) are not included, while several new commands are. See Differences from AT&T ms, for more information.

General structure of an ms document
-----------------------------------

The ms macro package expects a certain amount of structure, but not as much as packages such as man or mdoc.

The simplest documents can begin with a paragraph macro (such as LP or PP), and consist of text separated by paragraph macros or even blank lines.  Longer documents have a structure as follows:

Document type
     If you invoke the RP (report) macro on the first line of the document, groff prints the cover page information on its own page; otherwise it prints the information on the first page with your document text immediately following.  Other document formats found in AT&T troff are specific to AT&T or Berkeley, and are not supported in groff.

Format and layout
     By setting number registers, you can change your document's type (font and size), margins, spacing, headers and footers, and footnotes. See ms Document Control Registers, for more details.

Cover page
     A cover page consists of a title, the author's name and institution, an abstract, and the date. (Actually, only the title is required.) See ms Cover Page Macros, for more details.

Body
     Following the cover page is your document.  You can use the ms macros to write reports, letters, books, and so forth.  The package is designed for structured documents, consisting of paragraphs interspersed with headings and augmented by lists, footnotes, tables, and other common constructs.  See ms Body Text, for more details.

Table of contents
     Longer documents usually include a table of contents, which you can invoke by placing the TC macro at the end of your document.  The ms macros have minimal indexing facilities, consisting of the IX macro, which prints an entry on standard error.  Printing the table of contents at the end is necessary since groff is a single-pass text formatter, thus it cannot determine the page number of each section until that section has actually been set and printed. Since ms output is intended for hardcopy, you can manually relocate the pages containing the table of contents between the cover page and the body text after printing.

Document control registers
--------------------------

The following is a list of document control number registers.  For the sake of consistency, set registers related to margins at the beginning of your document, or just after the RP macro.  You can set other registers later in your document, but you should keep them together at the beginning to make them easy to find and edit as necessary.

Margin Settings
...............

 -- Register: \n[PO, ms]
     Defines the page offset (i.e., the left margin).  There is no explicit right margin setting; the combination of the PO and LL registers implicitly define the right margin width.

     Effective: next page.

     Default value: 1i.

 -- Register: \n[LL, ms]
     Defines the line length (i.e., the width of the body text).

     Effective: next paragraph.

     Default: 6i.

 -- Register: \n[LT, ms]
     Defines the title length (i.e., the header and footer width).  This is usually the same as LL, but not necessarily.

     Effective: next paragraph.

     Default: 6i.

 -- Register: \n[HM, ms]
     Defines the header margin height at the top of the page.

     Effective: next page.

     Default: 1i.

 -- Register: \n[FM, ms]
     Defines the footer margin height at the bottom of the page.

     Effective: next page.

     Default: 1i.

Text Settings
.............

 -- Register: \n[PS, ms]
     Defines the point size of the body text.  If the value is larger than or equal to 1000, divide it by 1000 to get a fractional point size.  For example, .nr PS 10250 sets the document's point size to 10.25p.

     Effective: next paragraph.

     Default: 10p.

 -- Register: \n[VS, ms]
     Defines the space between lines (line height plus leading).  If the value is larger than or equal to 1000, divide it by 1000 to get a fractional point size.  Due to backwards compatibility, VS must be smaller than 40000 (this is 40.0p).

     Effective: next paragraph.

     Default: 12p.

 -- Register: \n[PSINCR, ms]
     Defines an increment in point size, which is applied to section headings at nesting levels below the value specified in GROWPS.  The value of PSINCR should be specified in points, with the p scaling factor, and may include a fractional component; for example, .nr PSINCR 1.5p sets a point size increment of 1.5p.

     Effective: next section heading.

     Default: 1p.

 -- Register: \n[GROWPS, ms]
     Defines the heading level below which the point size increment set by PSINCR becomes effective.  Section headings at and above the level specified by GROWPS are printed at the point size set by PS; for each level below the value of GROWPS, the point size is increased in steps equal to the value of PSINCR.  Setting GROWPS to any value less than 2 disables the incremental heading size feature.

     Effective: next section heading.

     Default: 0.

 -- Register: \n[HY, ms]
     Defines the hyphenation level.  HY sets safely the value of the low-level hy register.  Setting the value of HY to 0 is equivalent to using the nh request.

     Effective: next paragraph.

     Default: 6.

 -- Register: \n[FAM, ms]
     Defines the font family used to typeset the document.

     Effective: next paragraph.

     Default: as defined in the output device.

Paragraph Settings
..................

 -- Register: \n[PI, ms]
     Defines the initial indentation of a (PP macro) paragraph.

     Effective: next paragraph.

     Default: 5n.

 -- Register: \n[PD, ms]
     Defines the space between paragraphs.

     Effective: next paragraph.

     Default: 0.3v.

 -- Register: \n[QI, ms]
     Defines the indentation on both sides of a quoted (QP, QS, and QE macros) paragraph.

     Effective: next paragraph.

     Default: 5n.

 -- Register: \n[PORPHANS, ms]
     Defines the minimum number of initial lines of any paragraph that should be kept together, to avoid orphan lines at the bottom of a page. If a new paragraph is started close to the bottom of a page, and there is insufficient space to accommodate PORPHANS lines before an automatic page break, then the page break is forced, before the start of the paragraph.

     Effective: next paragraph.

     Default: 1.

 -- Register: \n[HORPHANS, ms]
     Defines the minimum number of lines of the following paragraph that should be kept together with any section heading introduced by the NH or SH macros.  If a section heading is placed close to the bottom of a page, and there is insufficient space to accommodate both the heading and at least HORPHANS lines of the following paragraph, before an automatic page break, then the page break is forced before the heading.

     Effective: next paragraph.

     Default: 1.

Footnote Settings
.................

 -- Register: \n[FL, ms]
     Defines the length of a footnote.

     Effective: next footnote.

     Default: \n[LL] * 5 / 6.

 -- Register: \n[FI, ms]
     Defines the footnote indentation.

     Effective: next footnote.

     Default: 2n.

 -- Register: \n[FF, ms]
     The footnote format:

     0
          Print the footnote number as a superscript; indent the footnote (default).

     1
          Print the number followed by a period (like 1.) and indent the footnote.

     2
          Like 1, without an indentation.

     3
          Like 1, but print the footnote number as a hanging paragraph.

     Effective: next footnote.

     Default: 0.

 -- Register: \n[FPS, ms]
     Defines the footnote point size.  If the value is larger than or equal to 1000, divide it by 1000 to get a fractional point size.

     Effective: next footnote.

     Default: \n[PS] - 2.

 -- Register: \n[FVS, ms]
     Defines the footnote vertical spacing.  If the value is larger than or equal to 1000, divide it by 1000 to get a fractional point size.

     Effective: next footnote.

     Default: \n[FPS] + 2.

 -- Register: \n[FPD, ms]
     Defines the footnote paragraph spacing.

     Effective: next footnote.

     Default: \n[PD] / 2.

Miscellaneous Number Registers
..............................

 -- Register: \n[MINGW, ms]
     Defines the minimum width between columns in a multi-column document.

     Effective: next page.

     Default: 2n.

 -- Register: \n[DD, ms]
     Sets the vertical spacing before and after a display, a tbl table, an eqn equation, or a pic image.

     Effective: next paragraph.

     Default: 0.5v.

Cover page macros
-----------------

Use the following macros to create a cover page for your document in the order shown.

 -- Macro: .RP, [no], ms
     Specifies the report format for your document.  The report format creates a separate cover page.  The default action (no RP macro) is to print a subset of the cover page on page 1 of your document.

     If you use the word no as an optional argument, groff prints a title page but does not repeat any of the title page information (title, author, abstract, etc.) on page 1 of the document.

 -- Macro: .P1, , ms
     (P-one) Prints the header on page 1.  The default is to suppress the header.

 -- Macro: .DA, [...], ms
     (optional) Prints the current date, or the arguments to the macro if any, on the title page (if specified) and in the footers.  This is the default for nroff.

 -- Macro: .ND, [...], ms
     (optional) Prints the current date, or the arguments to the macro if any, on the title page (if specified) but not in the footers.  This is the default for troff.

 -- Macro: .TL, , ms
     Specifies the document title.  groff collects text following the TL macro into the title, until reaching the author name or abstract.

 -- Macro: .AU, , ms
     Specifies the author's name, which appears on the line (or lines) immediately following.  You can specify multiple authors as follows:

          .AU
          John Doe
          .AI
          University of West Bumblefuzz
          .AU
          Martha Buck
          .AI
          Monolithic Corporation

          ...

 -- Macro: .AI, , ms
     Specifies the author's institution.  You can specify multiple institutions in the same way that you specify multiple authors.

 -- Macro: .AB, [no], ms
     Begins the abstract.  The default is to print the word ABSTRACT, centered and in italics, above the text of the abstract.  The word no as an optional argument suppresses this heading.

 -- Macro: .AE, , ms
     Ends the abstract.

The following is example mark-up for a title page.

     .RP
     .TL
     The Inevitability of Code Bloat
     in Commercial and Free Software
     .AU
     J. Random Luser
     .AI
     University of West Bumblefuzz
     .AB
     This report examines the long-term growth
     of the code bases in two large, popular software
     packages; the free Emacs and the commercial
     Microsoft Word.
     While differences appear in the type or order
     of features added, due to the different
     methodologies used, the results are the same
     in the end.
     .PP
     The free software approach is shown to be
     superior in that while free software can
     become as bloated as commercial offerings,
     free software tends to have fewer serious
     bugs and the added features are in line with
     user demand.
     .AE

     ... the rest of the paper follows ...

Body text
---------

This section describes macros used to mark up the body of your document. Examples include paragraphs, sections, and other groups.

Paragraphs
..........

The following paragraph types are available.

 -- Macro: .PP, , ms
     Sets a paragraph with an initial indentation.

 -- Macro: .LP, , ms
     Sets a paragraph without an initial indentation.

 -- Macro: .QP, , ms
     Sets a paragraph that is indented at both left and right margins by the amount of the register QI. The effect is identical to the HTML <BLOCKQUOTE> element. The next paragraph or heading returns margins to normal. QP inserts vertical space of amount set by register PD before the paragraph.

 -- Macro: .QS, , ms
 -- Macro: .QE, , ms
     These macros begin and end a quoted section. The QI register controls the amount of indentation. Both QS and QE insert inter-paragraph vertical space set by register PD. The text between QS and QE can be structured further by use of the macros LP or PP.

 -- Macro: .XP, , ms
     Sets a paragraph whose lines are indented, except for the first line. This is a Berkeley extension.

The following markup uses all four paragraph macros.

     .NH 2
     Cases used in the study
     .LP
     The following software and versions were
     considered for this report.
     .PP
     For commercial software, we chose
     .B "Microsoft Word for Windows" ,
     starting with version 1.0 through the
     current version (Word 2000).
     .PP
     For free software, we chose
     .B Emacs ,
     from its first appearance as a standalone
     editor through the current version (v20).
     See [Bloggs 2002] for details.
     .QP
     Franklin's Law applied to software:
     software expands to outgrow both
     RAM and disk space over time.
     .LP
     Bibliography:
     .XP
     Bloggs, Joseph R.,
     .I "Everyone's a Critic" ,
     Underground Press, March 2002.
     A definitive work that answers all questions
     and criticisms about the quality and usability of
     free software.

The PORPHANS register (see ms Document Control Registers) operates in conjunction with each of these macros, to inhibit the printing of orphan lines at the bottom of any page.

Headings
........

Use headings to create a hierarchical structure for your document.  The ms macros print headings in bold, using the same font family and point size as the body text.

The following describes the heading macros:

 -- Macro: .NH, curr-level, ms
 -- Macro: .NH, S level0 ..., ms
     Numbered heading.  The argument is either a numeric argument to indicate the level of the heading, or the letter S followed by numeric arguments to set the heading level explicitly.

     If you specify heading levels out of sequence, such as invoking .NH 3 after .NH 1, groff prints a warning on standard error.

 -- String: \*[SN, ms]
 -- String: \*[SN-DOT, ms]
 -- String: \*[SN-NO-DOT, ms]
     After invocation of NH, the assigned section number is made available in the strings SN-DOT (as it appears in a printed section heading with default formatting, followed by a terminating period), and SN-NO-DOT (with the terminating period omitted). The string SN is also defined, as an alias for SN-DOT; if preferred, you may redefine it as an alias for SN-NO-DOT, by including the initialization

          .als SN SN-NO-DOT

     at any time before you would like the change to take effect.

 -- String: \*[SN-STYLE, ms]
     You may control the style used to print section numbers, within numbered section headings, by defining an appropriate alias for the string SN-STYLE.  The default style, in which the printed section number is followed by a terminating period, is obtained by defining the alias

          .als SN-STYLE SN-DOT

     If you prefer to omit the terminating period, from section numbers appearing in numbered section headings, you may define the alias

          .als SN-STYLE SN-NO-DOT

     Any such change in section numbering style becomes effective from the next use of .NH, following redefinition of the alias for SN-STYLE.

 -- Macro: .SH, [match-level], ms
     Unnumbered subheading.

     The optional MATCH-LEVEL argument is a GNU extension.  It is a number indicating the level of the heading, in a manner analogous to the CURR-LEVEL argument to .NH.  Its purpose is to match the point size, at which the heading is printed, to the size of a numbered heading at the same level, when the GROWPS and PSINCR heading size adjustment mechanism is in effect.  See ms Document Control Registers.

The HORPHANS register (see ms Document Control Registers) operates in conjunction with the NH and SH macros, to inhibit the printing of orphaned section headings at the bottom of any page.

Highlighting
............

The ms macros provide a variety of methods to highlight or emphasize text:

 -- Macro: .B, [txt [post [pre]]], ms
     Sets its first argument in bold type.  If you specify a second argument, groff prints it in the previous font after the bold text, with no intervening space (this allows you to set punctuation after the highlighted text without highlighting the punctuation). Similarly, it prints the third argument (if any) in the previous font before the first argument.  For example,

          .B foo ) (

     prints (foo).

     If you give this macro no arguments, groff prints all text following in bold until the next highlighting, paragraph, or heading macro.

 -- Macro: .R, [txt [post [pre]]], ms
     Sets its first argument in roman (or regular) type.  It operates similarly to the B macro otherwise.

 -- Macro: .I, [txt [post [pre]]], ms
     Sets its first argument in italic type.  It operates similarly to the B macro otherwise.

 -- Macro: .CW, [txt [post [pre]]], ms
     Sets its first argument in a constant width face.  It operates similarly to the B macro otherwise.

 -- Macro: .BI, [txt [post [pre]]], ms
     Sets its first argument in bold italic type.  It operates similarly to the B macro otherwise.

 -- Macro: .BX, [txt], ms
     Prints its argument and draws a box around it.  If you want to box a string that contains spaces, use a digit-width space (\0).

 -- Macro: .UL, [txt [post]], ms
     Prints its first argument with an underline.  If you specify a second argument, groff prints it in the previous font after the underlined text, with no intervening space.

 -- Macro: .LG, , ms
     Prints all text following in larger type (two points larger than the current point size) until the next font size, highlighting, paragraph, or heading macro.  You can specify this macro multiple times to enlarge the point size as needed.

 -- Macro: .SM, , ms
     Prints all text following in smaller type (two points smaller than the current point size) until the next type size, highlighting, paragraph, or heading macro.  You can specify this macro multiple times to reduce the point size as needed.

 -- Macro: .NL, , ms
     Prints all text following in the normal point size (that is, the value of the PS register).

 -- String: \*[{, ms]
 -- String: \*[}, ms]
     Text enclosed with \*{ and \*} is printed as a superscript.

Lists
.....

The IP macro handles duties for all lists.

 -- Macro: .IP, [marker [width]], ms
     The MARKER is usually a bullet glyph (\[bu]) for unordered lists, a number (or auto-incrementing number register) for numbered lists, or a word or phrase for indented (glossary-style) lists.

     The WIDTH specifies the indentation for the body of each list item; its default unit is n.  Once specified, the indentation remains the same for all list items in the document until specified again.

     The PORPHANS register (see ms Document Control Registers) operates in conjunction with the IP macro, to inhibit the printing of orphaned list markers at the bottom of any page.

The following is an example of a bulleted list.

     A bulleted list:
     .IP \[bu] 2
     lawyers
     .IP \[bu]
     guns
     .IP \[bu]
     money

Produces:

     A bulleted list:

     o lawyers

     o guns

     o money

The following is an example of a numbered list.

     .nr step 1 1
     A numbered list:
     .IP \n[step] 3
     lawyers
     .IP \n+[step]
     guns
     .IP \n+[step]
     money

Produces:

     A numbered list:

     1. lawyers

     2. guns

     3. money

Note the use of the auto-incrementing number register in this example.

The following is an example of a glossary-style list.

     A glossary-style list:
     .IP lawyers 0.4i
     Two or more attorneys.
     .IP guns
     Firearms, preferably
     large-caliber.
     .IP money
     Gotta pay for those
     lawyers and guns!

Produces:

     A glossary-style list:

     lawyers
           Two or more attorneys.

     guns  Firearms, preferably large-caliber.

     money
           Gotta pay for those lawyers and guns!

In the last example, the IP macro places the definition on the same line as the term if it has enough space; otherwise, it breaks to the next line and starts the definition below the term.  This may or may not be the effect you want, especially if some of the definitions break and some do not.  The following examples show two possible ways to force a break.

The first workaround uses the br request to force a break after printing the term or label.

     A glossary-style list:
     .IP lawyers 0.4i
     Two or more attorneys.
     .IP guns
     .br
     Firearms, preferably large-caliber.
     .IP money
     Gotta pay for those lawyers and guns!

The second workaround uses the \p escape to force the break. Note the space following the escape; this is important.  If you omit the space, groff prints the first word on the same line as the term or label (if it fits) then breaks the line.

     A glossary-style list:
     .IP lawyers 0.4i
     Two or more attorneys.
     .IP guns
     \p Firearms, preferably large-caliber.
     .IP money
     Gotta pay for those lawyers and guns!

To set nested lists, use the RS and RE macros. See Indentation values in ms, for more information.

For example:

     .IP \[bu] 2
     Lawyers:
     .RS
     .IP \[bu]
     Dewey,
     .IP \[bu]
     Cheatham,
     .IP \[bu]
     and Howe.
     .RE
     .IP \[bu]
     Guns

Produces:

     o Lawyers:

       o  Dewey,

       o  Cheatham,

       o  and Howe.

     o Guns

Indentation values
..................

In many situations, you may need to indentation a section of text while still wrapping and filling.  See Lists in ms, for an example of nested lists.

 -- Macro: .RS, , ms
 -- Macro: .RE, , ms
     These macros begin and end an indented section.  The PI register controls the amount of indentation, allowing the indented text to line up under hanging and indented paragraphs.

See ms Displays and Keeps, for macros to indentation and turn off filling.

Tab Stops
.........

Use the ta request to define tab stops as needed.  See Tabs and Fields.

 -- Macro: .TA, , ms
     Use this macro to reset the tab stops to the default for ms (every 5n).  You can redefine the TA macro to create a different set of default tab stops.

Displays and keeps
..................

Use displays to show text-based examples or figures (such as code listings).

Displays turn off filling, so lines of code are displayed as-is without inserting br requests in between each line.  Displays can be kept on a single page, or allowed to break across pages.

 -- Macro: .DS, L, ms
 -- Macro: .LD, , ms
 -- Macro: .DE, , ms
     Left-justified display.  The .DS L call generates a page break, if necessary, to keep the entire display on one page.  The LD macro allows the display to break across pages.  The DE macro ends the display.

 -- Macro: .DS, I, ms
 -- Macro: .ID, , ms
 -- Macro: .DE, , ms
     Indents the display as defined by the DI register.  The .DS I call generates a page break, if necessary, to keep the entire display on one page.  The ID macro allows the display to break across pages.  The DE macro ends the display.

 -- Macro: .DS, B, ms
 -- Macro: .BD, , ms
 -- Macro: .DE, , ms
     Sets a block-centered display: the entire display is left-justified, but indented so that the longest line in the display is centered on the page.  The .DS B call generates a page break, if necessary, to keep the entire display on one page.  The BD macro allows the display to break across pages.  The DE macro ends the display.

 -- Macro: .DS, C, ms
 -- Macro: .CD, , ms
 -- Macro: .DE, , ms
     Sets a centered display: each line in the display is centered.  The .DS C call generates a page break, if necessary, to keep the entire display on one page.  The CD macro allows the display to break across pages.  The DE macro ends the display.

 -- Macro: .DS, R, ms
 -- Macro: .RD, , ms
 -- Macro: .DE, , ms
     Right-justifies each line in the display.  The .DS R call generates a page break, if necessary, to keep the entire display on one page.  The RD macro allows the display to break across pages. The DE macro ends the display.

 -- Macro: .Ds, , ms
 -- Macro: .De, , ms
     These two macros were formerly provided as aliases for DS and DE, respectively.  They have been removed, and should no longer be used.  The original implementations of DS and DE are retained, and should be used instead.  X11 documents that actually use Ds and De always load a specific macro file from the X11 distribution (macros.t) that provides proper definitions for the two macros.

On occasion, you may want to keep other text together on a page. For example, you may want to keep two paragraphs together, or a paragraph that refers to a table (or list, or other item) immediately following.  The ms macros provide the KS and KE macros for this purpose.

 -- Macro: .KS, , ms
 -- Macro: .KE, , ms
     The KS macro begins a block of text to be kept on a single page, and the KE macro ends the block.

 -- Macro: .KF, , ms
 -- Macro: .KE, , ms
     Specifies a floating keep; if the keep cannot fit on the current page, groff holds the contents of the keep and allows text following the keep (in the source file) to fill in the remainder of the current page.  When the page breaks, whether by an explicit bp request or by reaching the end of the page, groff prints the floating keep at the top of the new page.  This is useful for printing large graphics or tables that do not need to appear exactly where specified.

You can also use the ne request to force a page break if there is not enough vertical space remaining on the page.

Use the following macros to draw a box around a section of text (such as a display).

 -- Macro: .B1, , ms
 -- Macro: .B2, , ms
     Marks the beginning and ending of text that is to have a box drawn around it.  The B1 macro begins the box; the B2 macro ends it.  Text in the box is automatically placed in a diversion (keep).

Tables, figures, equations, and references
..........................................

The ms macros support the standard groff preprocessors: tbl, pic, eqn, and refer. You mark text meant for preprocessors by enclosing it in pairs of tags as follows.

 -- Macro: .TS, [H], ms
 -- Macro: .TE, , ms
     Denotes a table, to be processed by the tbl preprocessor.  The optional argument H to TS instructs groff to create a running header with the information up to the TH macro. groff prints the header at the beginning of the table; if the table runs onto another page, groff prints the header on the next page as well.

 -- Macro: .PS, , ms
 -- Macro: .PE, , ms
     Denotes a graphic, to be processed by the pic preprocessor.  You can create a pic file by hand, using the AT&T pic manual available on the Web as a reference, or by using a graphics program such as xfig.

 -- Macro: .EQ, [align], ms
 -- Macro: .EN, , ms
     Denotes an equation, to be processed by the eqn preprocessor. The optional ALIGN argument can be C, L, or I to center (the default), left-justify, or indent the equation.

 -- Macro: .[, , ms
 -- Macro: .], , ms
     Denotes a reference, to be processed by the refer preprocessor. The GNU refer(1) man page provides a comprehensive reference to the preprocessor and the format of the bibliographic database.

An example multi-page table
...........................

The following is an example of how to set up a table that may print across two or more pages.

     .TS H
     allbox expand;
     cb | cb .
     Text      ...of heading...
     _
     .TH
     .T&
     l | l .
     ... the rest of the table follows...
     .CW
     .TE

Footnotes
.........

The ms macro package has a flexible footnote system.  You can specify either numbered footnotes or symbolic footnotes (that is, using a marker such as a dagger symbol).

 -- String: \*[*, ms]
     Specifies the location of a numbered footnote marker in the text.

 -- Macro: .FS, , ms
 -- Macro: .FE, , ms
     Specifies the text of the footnote.  The default action is to create a numbered footnote; you can create a symbolic footnote by specifying a mark glyph (such as \[dg] for the dagger glyph) in the body text and as an argument to the FS macro, followed by the text of the footnote and the FE macro.

You can control how groff prints footnote numbers by changing the value of the FF register.  See ms Document Control Registers.

Footnotes can be safely used within keeps and displays, but you should avoid using numbered footnotes within floating keeps.  You can set a second \** marker between a \** and its corresponding .FS entry; as long as each FS macro occurs after the corresponding \** and the occurrences of .FS are in the same order as the corresponding occurrences of \**.

Page layout
-----------

The default output from the ms macros provides a minimalist page layout: it prints a single column, with the page number centered at the top of each page.  It prints no footers.

You can change the layout by setting the proper number registers and strings.

Headers and footers
...................

For documents that do not distinguish between odd and even pages, set the following strings:

 -- String: \*[LH, ms]
 -- String: \*[CH, ms]
 -- String: \*[RH, ms]
     Sets the left, center, and right headers.

 -- String: \*[LF, ms]
 -- String: \*[CF, ms]
 -- String: \*[RF, ms]
     Sets the left, center, and right footers.

For documents that need different information printed in the even and odd pages, use the following macros:

 -- Macro: .OH, 'left'center'right', ms
 -- Macro: .EH, 'left'center'right', ms
 -- Macro: .OF, 'left'center'right', ms
 -- Macro: .EF, 'left'center'right', ms
     The OH and EH macros define headers for the odd and even pages; the OF and EF macros define footers for the odd and even pages.  This is more flexible than defining the individual strings.

     You can replace the quote (') marks with any character not appearing in the header or footer text.

To specify custom header and footer processing, redefine the following macros:

 -- Macro: .PT,, ms
 -- Macro: .HD,, ms
 -- Macro: .BT,, ms
     The PT macro defines a custom header; the BT macro defines a custom footer.  These macros must handle odd/even/first page differences if necessary.

     The HD macro defines additional header processing to take place after executing the PT macro.

Margins
.......

You control margins using a set of number registers.  See ms Document Control Registers, for details.

Multiple columns
................

The ms macros can set text in as many columns as do reasonably fit on the page.  The following macros are available; all of them force a page break if a multi-column mode is already set.  However, if the current mode is single-column, starting a multi-column mode does not force a page break.

 -- Macro: .1C, , ms
     Single-column mode.

 -- Macro: .2C, , ms
     Two-column mode.

 -- Macro: .MC, [width [gutter]], ms
     Multi-column mode.  If you specify no arguments, it is equivalent to the 2C macro.  Otherwise, WIDTH is the width of each column and GUTTER is the space between columns.  The MINGW number register controls the default gutter width.

Creating a table of contents
............................

The facilities in the ms macro package for creating a table of contents are semi-automated at best.  Assuming that you want the table of contents to consist of the document's headings, you need to repeat those headings wrapped in XS and XE macros.

 -- Macro: .XS, [page], ms
 -- Macro: .XA, [page], ms
 -- Macro: .XE, , ms
     These macros define a table of contents or an individual entry in the table of contents, depending on their use.  The macros are very simple; they cannot indent a heading based on its level.  The easiest way to work around this is to add tabs to the table of contents string.  The following is an example:

          .NH 1
          Introduction
          .XS
          Introduction
          .XE
          .LP
          ...
          .CW
          .NH 2
          Methodology
          .XS
          Methodology
          .XE
          .LP
          ...

     You can manually create a table of contents by beginning with the XS macro for the first entry, specifying the page number for that entry as the argument to XS.  Add subsequent entries using the XA macro, specifying the page number for that entry as the argument to XA.  The following is an example:

          .XS 1
          Introduction
          .XA 2
          A Brief History of the Universe
          .XA 729
          Details of Galactic Formation
          ...
          .XE

 -- Macro: .TC, [no], ms
     Prints the table of contents on a new page, setting the page number to i (Roman lowercase numeral one).  You should usually place this macro at the end of the file, since groff is a single-pass formatter and can only print what has been collected up to the point that the TC macro appears.

     The optional argument no suppresses printing the title specified by the string register TOC.

 -- Macro: .PX, [no], ms
     Prints the table of contents on a new page, using the current page numbering sequence.  Use this macro to print a manually generated table of contents at the beginning of your document.

     The optional argument no suppresses printing the title specified by the string register TOC.

The Groff and Friends HOWTO includes a sed script that automatically inserts XS and XE macro entries after each heading in a document.

Altering the NH macro to automatically build the table of contents is perhaps initially more difficult, but would save a great deal of time in the long run if you use ms regularly.

Strings and Special Characters
..............................

The ms macros provide the following predefined strings.  You can change the string definitions to help in creating documents in languages other than English.

 -- String: \*[REFERENCES, ms]
     Contains the string printed at the beginning of the references (bibliography) page.  The default is References.

 -- String: \*[ABSTRACT, ms]
     Contains the string printed at the beginning of the abstract.  The default is ABSTRACT.

 -- String: \*[TOC, ms]
     Contains the string printed at the beginning of the table of contents.

 -- String: \*[MONTH1, ms]
 -- String: \*[MONTH2, ms]
 -- String: \*[MONTH3, ms]
 -- String: \*[MONTH4, ms]
 -- String: \*[MONTH5, ms]
 -- String: \*[MONTH6, ms]
 -- String: \*[MONTH7, ms]
 -- String: \*[MONTH8, ms]
 -- String: \*[MONTH9, ms]
 -- String: \*[MONTH10, ms]
 -- String: \*[MONTH11, ms]
 -- String: \*[MONTH12, ms]
     Prints the full name of the month in dates.  The default is January, February, etc.

The following special characters are available (For an explanation what special characters are see Special Characters.):

 -- String: \*[-, ms]
     Prints an em dash.

 -- String: \*[Q, ms]
 -- String: \*[U, ms]
     Prints typographer's quotes in troff, and plain quotes in nroff. \*Q is the left quote and \*U is the right quote.

Improved accent marks are available in the ms macros.

 -- Macro: .AM, , ms
     Specify this macro at the beginning of your document to enable extended accent marks and special characters.  This is a Berkeley extension.

     To use the accent marks, place them after the character being accented.

     Note that groff's native support for accents is superior to the following definitions.

The following accent marks are available after invoking the AM macro:

 -- String: \*[', ms]
     Acute accent.

 -- String: \*[`, ms]
     Grave accent.

 -- String: \*[^, ms]
     Circumflex.

 -- String: \*[\,, ms]
     Cedilla.

 -- String: \*[~, ms]
     Tilde.

 -- String: \*[:]
     Umlaut.

 -- String: \*[v, ms]
     Hacek.

 -- String: \*[_, ms]
     Macron (overbar).

 -- String: \*[., ms]
     Underdot.

 -- String: \*[o, ms]
     Ring above.

The following are standalone characters available after invoking the AM macro:

 -- String: \*[?, ms]
     Upside-down question mark.

 -- String: \*[!, ms]
     Upside-down exclamation point.

 -- String: \*[8, ms]
     German ß ligature.

 -- String: \*[3, ms]
     Yogh.

 -- String: \*[Th, ms]
     Uppercase thorn.

 -- String: \*[th, ms]
     Lowercase thorn.

 -- String: \*[D-, ms]
     Uppercase eth.

 -- String: \*[d-, ms]
     Lowercase eth.

 -- String: \*[q, ms]
     Hooked o.

 -- String: \*[ae, ms]
     Lowercase æ ligature.

 -- String: \*[Ae, ms]
     Uppercase Æ ligature.

Differences from AT&T ms
------------------------

This section lists the (minor) differences between the groff -ms macros and AT&T troff -ms macros.

  * The internals of groff -ms differ from the internals of AT&T troff -ms.  Documents that depend upon implementation details of AT&T troff -ms may not format properly with groff -ms.

  * The general error-handling policy of groff -ms is to detect and report errors, rather than silently to ignore them.

  * groff -ms does not work in compatibility mode (that is, with the -C option).

  * There is no special support for typewriter-like devices.

  * groff -ms does not provide cut marks.

  * Multiple line spacing is not supported.  Use a larger vertical spacing instead.

  * Some Unix ms documentation says that the CW and GW number registers can be used to control the column width and gutter width, respectively.  These number registers are not used in groff -ms.

  * Macros that cause a reset (paragraphs, headings, etc.) may change the indentation.  Macros that change the indentation do not increment or decrement the indentation, but rather set it absolutely.  This can cause problems for documents that define additional macros of their own.  The solution is to use not the in request but instead the RS and RE macros.

  * To make groff -ms use the default page offset (which also specifies the left margin), the PO register must stay undefined until the first -ms macro is evaluated.  This implies that PO should not be used early in the document, unless it is changed also: Remember that accessing an undefined register automatically defines it.

 -- Register: \n[GS, ms]
     This number register is set to 1 by the groff -ms macros, but it is not used by the AT&T troff -ms macros. Documents that need to determine whether they are being formatted with AT&T troff -ms or groff -ms should use this number register.

Emulations of a few ancient Bell Labs macros can be re-enabled by calling the otherwise undocumented SC section-header macro. Calling SC enables UC for marking up a product or application name, and the pair P1/P2 for surrounding code example displays.

These are not enabled by default because (a) they were not documented, in the original ms manual, and (b) the P1 and UC macros collide with different macros with the same names in the Berkeley version of ms.

These groff emulations are sufficient to give back the 1976 Kernighan & Cherry paper Typesetting Mathematics -- User's Guide its section headings, and restore some text that had gone missing as arguments of undefined macros.  No warranty express or implied is given as to how well the typographic details these produce match the original Bell Labs macros.

troff macros not appearing in groff
...................................

Macros missing from groff -ms are cover page macros specific to Bell Labs and Berkeley.  The macros known to be missing are:

.TM
     Technical memorandum; a cover sheet style

.IM
     Internal memorandum; a cover sheet style

.MR
     Memo for record; a cover sheet style

.MF
     Memo for file; a cover sheet style

.EG
     Engineer's notes; a cover sheet style

.TR
     Computing Science Tech Report; a cover sheet style

.OK
     Other keywords

.CS
     Cover sheet information

.MH
     A cover sheet macro

groff macros not appearing in AT&T troff
........................................

The groff -ms macros have a few minor extensions compared to the AT&T troff -ms macros.

 -- Macro: .AM, , ms
     Improved accent marks.  See ms Strings and Special Characters, for details.

 -- Macro: .DS, I, ms
     Indented display.  The default behavior of AT&T troff -ms was to indent; the groff default prints displays flush left with the body text.

 -- Macro: .CW, , ms
     Print text in constant width (Courier) font.

 -- Macro: .IX, , ms
     Indexing term (printed on standard error).  You can write a script to capture and process an index generated in this manner.

The following additional number registers appear in groff -ms:

 -- Register: \n[MINGW, ms]
     Specifies a minimum space between columns (for multi-column output); this takes the place of the GW register that was documented but apparently not implemented in AT&T troff.

Several new string registers are available as well.  You can change these to handle (for example) the local language.  See ms Strings and Special Characters, for details.

Naming Conventions
------------------

The following conventions are used for names of macros, strings and number registers.  External names available to documents that use the groff -ms macros contain only uppercase letters and digits.

Internally the macros are divided into modules; naming conventions are as follows:

  * Names used only within one module are of the form MODULE*NAME.

  * Names used outside the module in which they are defined are of the form MODULE@NAME.

  * Names associated with a particular environment are of the form ENVIRONMENT:NAME; these are used only within the par module.

  * NAME does not have a module prefix.

  * Constructed names used to implement arrays are of the form ARRAY!INDEX.

Thus the groff ms macros reserve the following names:

  * Names containing the characters *, @, and :.

  * Names containing only uppercase letters and digits.

me
==

See the meintro.me and meref.me documents in groff's doc directory.

mm
==

See the groff_mm(7) man page (type man groff_mm at the command line).

mom
===

The main documentation files for the mom macros are in HTML format.  Additional, useful documentation is in PDF format.  See the groff(1) man page, section ``Installation Directories'', for their location.

  * toc.html

     Entry point to the full mom manual.

  * macrolist.html

     Hyperlinked index of macros with brief descriptions, arranged by category.

  * mom-pdf.pdf

     PDF features and usage.

The mom macros are in active development between groff releases. The most recent version, along with up-to-date documentation, is available at http://www.schaffter.ca/mom/mom-05.html.

The groff_mom(7) man page (type man groff_mom at the command line) contains a partial list of available macros, however their usage is best understood by consulting the HTML documentation.

gtroff Reference
****************

This chapter covers all of the facilities of gtroff. Users of macro packages may skip it if not interested in details.

Text
====

gtroff input files contain text with control commands interspersed throughout.  But, even without control codes, gtroff still does several things with the input text:

  * filling and adjusting

  * adding additional space after sentences

  * hyphenating

  * inserting implicit line breaks

Filling and Adjusting
---------------------

When gtroff reads text, it collects words from the input and fits as many of them together on one output line as it can.  This is known as filling.

Once gtroff has a filled line, it tries to adjust it. This means it widens the spacing between words until the text reaches the right margin (in the default adjustment mode).  Extra spaces between words are preserved, but spaces at the end of lines are ignored.  Spaces at the front of a line cause a break (breaks are explained in Implicit Line Breaks).

See Manipulating Filling and Adjusting.

Hyphenation
-----------

Since the odds are not great for finding a set of words, for every output line, which fit nicely on a line without inserting excessive amounts of space between words, gtroff hyphenates words so that it can justify lines without inserting too much space between words.  It uses an internal hyphenation algorithm (a simplified version of the algorithm used within TeX) to indicate which words can be hyphenated and how to do so.  When a word is hyphenated, the first part of the word is added to the current filled line being output (with an attached hyphen), and the other portion is added to the next line to be filled.

See Manipulating Hyphenation.

Sentences
---------

Although it is often debated, some typesetting rules say there should be different amounts of space after various punctuation marks.  For example, the Chicago typesetting manual says that a period at the end of a sentence should have twice as much space following it as would a comma or a period as part of an abbreviation.

gtroff does this by flagging certain characters (normally !, ?, and .) as end-of-sentence characters. When gtroff encounters one of these characters at the end of a line, it appends a normal space followed by a sentence space in the formatted output.  (This justifies one of the conventions mentioned in Input Conventions.)

In addition, the following characters and symbols are treated transparently while handling end-of-sentence characters: ", ', ), ], *, \[dg], \[rq], and \[cq].

See the cflags request in Using Symbols, for more details.

To prevent the insertion of extra space after an end-of-sentence character (at the end of a line), append \&.

Tab Stops
---------

gtroff translates tabulator characters, also called tabs (normally code point ASCII 0x09 or EBCDIC 0x05), in the input into movements to the next tabulator stop.  These tab stops are initially located every half inch across the page.  Using this, simple tables can be made easily. However, it can often be deceptive as the appearance (and width) of the text on a terminal and the results from gtroff can vary greatly.

Also, a possible sticking point is that lines beginning with tab characters are still filled, again producing unexpected results.  For example, the following input

1   2   3

  4   5

produces

1   2   3       4   5

See Tabs and Fields.

Implicit Line Breaks
--------------------

An important concept in gtroff is the break.  When a break occurs, gtroff outputs the partially filled line (unjustified), and resumes collecting and filling text on the next output line.

There are several ways to cause a break in gtroff.  A blank line not only causes a break, but it also outputs a one-line vertical space (effectively a blank line).  Note that this behaviour can be modified with the blank line macro request blm.  See Blank Line Traps.

A line that begins with a space causes a break and the space is output at the beginning of the next line.  Note that this space isn't adjusted, even in fill mode; however, the behaviour can be modified with the leading spaces macro request lsm.  See Leading Spaces Traps.

The end of file also causes a break -- otherwise the last line of the document may vanish!

Certain requests also cause breaks, implicitly or explicitly.  This is discussed in Manipulating Filling and Adjusting.

Input Conventions
-----------------

Since gtroff does filling automatically, it is traditional in groff not to try and type things in as nicely formatted paragraphs.  These are some conventions commonly used when typing gtroff text:

  * Break lines after punctuation, particularly at the end of a sentence and in other logical places.  Keep separate phrases on lines by themselves, as entire phrases are often added or deleted when editing.

  * Try to keep lines less than 40--60 characters, to allow space for inserting more text.

  * Do not try to do any formatting in a WYSIWYG manner (i.e., don't try using spaces to get proper indentation).

Input Encodings
---------------

Currently, the following input encodings are available.

cp1047
     This input encoding works only on EBCDIC platforms (and vice versa, the other input encodings don't work with EBCDIC); the file cp1047.tmac is by default loaded at start-up.

latin-1
     This is the default input encoding on non-EBCDIC platforms; the file latin1.tmac is loaded at start-up.

latin-2
     To use this encoding, either say .mso latin2.tmac at the very beginning of your document or use -mlatin2 as a command-line argument for groff.

latin-5
     For Turkish.  Either say .mso latin5.tmac at the very beginning of your document or use -mlatin5 as a command-line argument for groff.

latin-9 (latin-0)
     This encoding is intended (at least in Europe) to replace latin-1 encoding.  The main difference to latin-1 is that latin-9 contains the Euro character.  To use this encoding, either say .mso latin9.tmac at the very beginning of your document or use -mlatin9 as a command-line argument for groff.

Note that it can happen that some input encoding characters are not available for a particular output device.  For example, saying

     groff -Tlatin1 -mlatin9 ...

fails if you use the Euro character in the input.  Usually, this limitation is present only for devices that have a limited set of output glyphs (e.g. -Tascii and -Tlatin1); for other devices it is usually sufficient to install proper fonts that contain the necessary glyphs.

Due to the importance of the Euro glyph in Europe, the groff package now comes with a POSTSCRIPT font called freeeuro.pfa, which provides various glyph shapes for the Euro.  In other words, latin-9 encoding is supported for the -Tps device out of the box (latin-2 isn't).

By its very nature, -Tutf8 supports all input encodings; -Tdvi has support for both latin-2 and latin-9 if the command-line -mec is used also to load the file ec.tmac (which flips to the EC fonts).

Measurements
============

gtroff (like many other programs) requires numeric parameters to specify various measurements.  Most numeric parameters (those that specify vertical or horizontal motion or a type size) may have a measurement unit attached.  These units are specified as a single character that immediately follows the number or expression.  Each of these units are understood, by gtroff, to be a multiple of its basic unit.  So, whenever a different measurement unit is specified gtroff converts this into its basic units.  This basic unit, represented by a u, is a device dependent measurement, which is quite small, ranging from 1/75th to 1/72000th of an inch.  The values may be given as fractional numbers; however, fractional basic units are always rounded to integers.

Some of the measurement units are completely independent of any of the current settings (e.g. type size) of gtroff.

Although groff's basic unit is device-dependent, it may still be smaller than the smallest unit the device is capable of producing.  The register .H specifies how many groff basic units constitute the current device's basic unit horizontally, and the register .V specifies this value vertically.

i
     Inches.  An antiquated measurement unit still in use in certain backwards countries with incredibly low-cost computer equipment.  One inch is defined to be 2.54 cm (worldwide since 1964).

c
     Centimeters.  One centimeter is about 0.3937 in.

p
     Points.  This is a typesetter's measurement used for measure type size. It is 72 points to an inch.

P
     Pica.  Another typesetting measurement.  6 picas to an inch (and 12 points to a pica).

s
z
     See Fractional Type Sizes, for a discussion of these units.

f
     Fractions.  Value is 65536. See Colors, for usage.

The other measurements understood by gtroff depend on settings currently in effect in gtroff.  These are very useful for specifying measurements that should look proper with any size of text.

m
     Ems.  This unit is equal to the current font size in points.  So called because it is approximately the width of the letter m in the current font.

n
     Ens.  In groff, this is half of an em.

v
     Vertical space.  This is equivalent to the current line spacing. See Sizes, for more information about this.

M
     100ths of an em.

Default Units
-------------

Many requests take a default unit.  While this can be helpful at times, it can cause strange errors in some expressions.  For example, the line length request expects em units.  Here are several attempts to get a line length of 3.5 inches and their results:

     3.5i      =>   3.5i
     7/2       =>   0i
     7/2i      =>   0i
     (7 / 2)u  =>   0i
     7i/2      =>   0.1i
     7i/2u     =>   3.5i

Everything is converted to basic units first.  In the above example it is assumed that 1i equals 240u, and 1m equals 10p (thus 1m equals 33u).  The value 7i/2 is first handled as 7i/2m, then converted to 1680u/66u, which is 25u, and this is approximately 0.1i.  As can be seen, a scaling indicator after a closing parenthesis is simply ignored.

Thus, the safest way to specify measurements is to always attach a scaling indicator.  If you want to multiply or divide by a certain scalar value, use u as the unit for that value.

Expressions
===========

gtroff has most arithmetic operators common to other languages:

  * Arithmetic: + (addition), - (subtraction), / (division), * (multiplication), % (modulo).

     gtroff only provides integer arithmetic.  The internal type used for computing results is int, which is usually a 32-bit signed integer.

  * Comparison: < (less than), > (greater than), <= (less than or equal), >= (greater than or equal), = (equal), == (the same as =).

  * Logical: & (logical and), : (logical or).

  * Unary operators: - (negating, i.e. changing the sign), + (just for completeness; does nothing in expressions), ! (logical not; this works only within if and while requests). (Note that, for example, !(-1) evaluates to `true' because gtroff treats both negative numbers and zero as `false'.)  See below for the use of unary operators in motion requests.

     The logical not operator, as described above, works only within if and while requests. Furthermore, it may appear only at the beginning of an expression, and negates the entire expression. Attempting to insert the ! operator within the expression results in a numeric expression expected warning.  This maintains compatibility with old versions of troff.

     Example:

          .nr X 1
          .nr Y 0
          .\" This does not work as expected
          .if (\n[X])&(!\n[Y]) .nop X only
          .
          .\" Use this construct instead
          .if (\n[X]=1)&(\n[Y]=0) .nop X only

  * Extrema: >? (maximum), <? (minimum).

     Example:

          .nr x 5
          .nr y 3
          .nr z (\n[x] >? \n[y])

     The register z now contains 5.

  * Scaling: (C;E).  Evaluate E using C as the default scaling indicator.  If C is missing, ignore scaling indicators in the evaluation of E.

Parentheses may be used as in any other language.  However, in gtroff they are necessary to ensure order of evaluation. gtroff has no operator precedence; expressions are evaluated left to right.  This means that gtroff evaluates 3+5*4 as if it were parenthesized like (3+5)*4, not as 3+(5*4), as might be expected.

For many requests that cause a motion on the page, the unary operators + and - work differently if leading an expression.  They then indicate a motion relative to the current position (down or up, respectively).

Similarly, a leading | operator indicates an absolute position. For vertical movements, it specifies the distance from the top of the page; for horizontal movements, it gives the distance from the beginning of the input line.

+ and - are also treated differently by the following requests and escapes: bp, in, ll, lt, nm, nr, pl, pn, po, ps, pvs, rt, ti, \H, \R, and \s. Here, leading plus and minus signs indicate increments and decrements.

See Setting Registers, for some examples.

 -- Escape: \\B, ', anything, '
     Return 1 if ANYTHING is a valid numeric expression; or 0 if ANYTHING is empty or not a valid numeric expression.

Due to the way arguments are parsed, spaces are not allowed in expressions, unless the entire expression is surrounded by parentheses.

See Request and Macro Arguments, and Conditionals and Loops.

Identifiers
===========

Like any other language, gtroff has rules for properly formed identifiers.  In gtroff, an identifier can be made up of almost any printable character, with the exception of the following characters:

  * Whitespace characters (spaces, tabs, and newlines).

  * Backspace (ASCII 0x08 or EBCDIC 0x16) and character code 0x01.

  * The following input characters are invalid and are ignored if groff runs on a machine based on ASCII, causing a warning message of type input (see Debugging, for more details): 0x00, 0x0B, 0x0D--0x1F, 0x80--0x9F.

     And here are the invalid input characters if groff runs on an EBCDIC host: 0x00, 0x08, 0x09, 0x0B, 0x0D--0x14, 0x17--0x1F, 0x30--0x3F.

     Currently, some of these reserved codepoints are used internally, thus making it non-trivial to extend gtroff to cover Unicode or other character sets and encodings that use characters of these ranges.

     Note that invalid characters are removed before parsing; an identifier foo, followed by an invalid character, followed by bar is treated as foobar.

For example, any of the following is valid.

     br
     PP
     (l
     end-list
     @_

Note that identifiers longer than two characters with a closing bracket (]) in its name can't be accessed with escape sequences that expect an identifier as a parameter.  For example, \[foo]] accesses the glyph foo, followed by ], whereas \C'foo]' really asks for glyph foo].

To avoid problems with the refer preprocessor, macro names should not start with [ or ].  Due to backwards compatibility, everything after .[ and .] is handled as a special argument to refer.  For example, .[foo makes refer to start a reference, using foo as a parameter.

 -- Escape: \\A, ', ident, '
     Test whether an identifier IDENT is valid in gtroff.  It expands to the character 1 or 0 according to whether its argument (usually delimited by quotes) is or is not acceptable as the name of a string, macro, diversion, number register, environment, or font.  It returns 0 if no argument is given.  This is useful for looking up user input in some sort of associative table.

          \A'end-list'
              => 1

See Escapes, for details on parameter delimiting characters.

Identifiers in gtroff can be any length, but, in some contexts, gtroff needs to be told where identifiers end and text begins (and in different ways depending on their length):

  * Single character.

  * Two characters.  Must be prefixed with ( in some situations.

  * Arbitrary length (gtroff only).  Must be bracketed with [ and ] in some situations.  Any length identifier can be put in brackets.

Unlike many other programming languages, undefined identifiers are silently ignored or expanded to nothing.  When gtroff finds an undefined identifier, it emits a warning, doing the following:

  * If the identifier is a string, macro, or diversion, gtroff defines it as empty.

  * If the identifier is a number register, gtroff defines it with a value of 0.

See Warnings., Interpolating Registers, and Strings.

Note that macros, strings, and diversions share the same name space.

     .de xxx
     .  nop foo
     ..
     .
     .di xxx
     bar
     .br
     .di
     .
     .xxx
         => bar

As can be seen in the previous example, gtroff reuses the identifier xxx, changing it from a macro to a diversion.  No warning is emitted!  The contents of the first macro definition is lost.

See Interpolating Registers, and Strings.

Embedded Commands
=================

Most documents need more functionality beyond filling, adjusting and implicit line breaking.  In order to gain further functionality, gtroff allows commands to be embedded into the text, in two ways.

The first is a request that takes up an entire line, and does some large-scale operation (e.g. break lines, start new pages).

The other is an escape that can be usually embedded anywhere in the text; most requests can accept it even as an argument.  Escapes generally do more minor operations like sub- and superscripts, print a symbol, etc.

Requests
--------

A request line begins with a control character, which is either a single quote (', the no-break control character) or a period (., the normal control character).  These can be changed; see Character Translations, for details.  After this there may be optional tabs or spaces followed by an identifier, which is the name of the request.  This may be followed by any number of space-separated arguments (no tabs here).

Since a control character followed by whitespace only is ignored, it is common practice to use this feature for structuring the source code of documents or macro packages.

     .de foo
     .  tm This is foo.
     ..
     .
     .
     .de bar
     .  tm This is bar.
     ..

Another possibility is to use the blank line macro request blm by assigning an empty macro to it.

     .de do-nothing
     ..
     .blm do-nothing  \" activate blank line macro

     .de foo
     .  tm This is foo.
     ..

     .de bar
     .  tm This is bar.
     ..

     .blm             \" deactivate blank line macro

See Blank Line Traps.

To begin a line with a control character without it being interpreted, precede it with \&.  This represents a zero width space, which means it does not affect the output.

In most cases the period is used as a control character.  Several requests cause a break implicitly; using the single quote control character prevents this.

 -- Register: \n[.br]
     A read-only number register, which is set to 1 if a macro is called with the normal control character (as defined with the cc request), and set to 0 otherwise.

     This allows reliable modification of requests.

          .als bp*orig bp
          .de bp
          .  tm before bp
          .  ie \\n[.br] .bp*orig
          .  el 'bp*orig
          .  tm after bp
          ..

     Using this register outside of a macro makes no sense (it always returns zero in such cases).

     If a macro is called as a string (that is, using \*), the value of the .br register is inherited from the caller.

Request and Macro Arguments
...........................

Arguments to requests and macros are processed much like the shell: The line is split into arguments according to spaces. (Plan 9's troff implementation also allows tabs for argument separation -- gtroff intentionally doesn't support this.)

An argument to a macro that is intended to contain spaces can either be enclosed in double quotes, or have the spaces escaped with backslashes.  This is not true for requests.

Here are a few examples for a hypothetical macro uh:

     .uh The Mouse Problem
     .uh "The Mouse Problem"
     .uh The\ Mouse\ Problem

The first line is the uh macro being called with 3 arguments, The, Mouse, and Problem.  The latter two have the same effect of calling the uh macro with one argument, The Mouse Problem. (The last solution, i.e., using escaped spaces, is ``classical'' in the sense that it can be found in most troff documents.  Nevertheless, it is not optimal in all situations, since \  inserts a fixed-width, non-breaking space character that can't stretch.  gtroff provides a different command \~ to insert a stretchable, non-breaking space.)

A double quote that isn't preceded by a space doesn't start a macro argument.  If not closing a string, it is printed literally.

For example,

     .xxx a" "b c" "de"fg"

has the arguments a", b c, de, and fg". Don't rely on this obscure behaviour!

There are two possibilities to get a double quote reliably.

  * Enclose the whole argument with double quotes and use two consecutive double quotes to represent a single one.  This traditional solution has the disadvantage that double quotes don't survive argument expansion again if called in compatibility mode (using the -C option of groff):

          .de xx
          .  tm xx: `\\$1' `\\$2' `\\$3'
          .
          .  yy "\\$1" "\\$2" "\\$3"
          ..
          .de yy
          .  tm yy: `\\$1' `\\$2' `\\$3'
          ..
          .xx A "test with ""quotes""" .
              => xx: `A' `test with "quotes"' `.'
              => yy: `A' `test with ' `quotes""'

     If not in compatibility mode, you get the expected result

          xx: `A' `test with "quotes"' `.'
          yy: `A' `test with "quotes"' `.'

     since gtroff preserves the input level.

  * Use the double quote glyph \(dq.  This works with and without compatibility mode enabled since gtroff doesn't convert \(dq back to a double quote input character.

     Note that this method won't work with Unix troff in general since the glyph `dq' isn't defined normally.

Double quotes in the ds request are handled differently. See Strings, for more details.

Macros
------

gtroff has a macro facility for defining a series of lines that can be invoked by name.  They are called in the same manner as requests -- arguments also may be passed basically in the same manner.

See Writing Macros, and Request and Macro Arguments.

Escapes
-------

Escapes may occur anywhere in the input to gtroff.  They usually begin with a backslash and are followed by a single character, which indicates the function to be performed.  The escape character can be changed; see Character Translations.

Escape sequences that require an identifier as a parameter accept three possible syntax forms.

  * The next single character is the identifier.

  * If this single character is an opening parenthesis, take the following two characters as the identifier.  Note that there is no closing parenthesis after the identifier.

  * If this single character is an opening bracket, take all characters until a closing bracket as the identifier.

Examples:

     \fB
     \n(XX
     \*[TeX]

Other escapes may require several arguments and/or some special format. In such cases the argument is traditionally enclosed in single quotes (and quotes are always used in this manual for the definitions of escape sequences).  The enclosed text is then processed according to what that escape expects.  Example:

     \l'1.5i\(bu'

Note that the quote character can be replaced with any other character that does not occur in the argument (even a newline or a space character) in the following escapes: \o, \b, and \X.  This makes e.g.

     A caf
     \o
     e\'

     in Paris
       => A café in Paris

possible, but it is better not to use this feature to avoid confusion.

The following escape sequences (which are handled similarly to characters since they don't take a parameter) are also allowed as delimiters: \%, \ , \|, \^, \{, \}, \', \`, \-, \_, \!, \?, \), \/, \,, \&, \:, \~, \0, \a, \c, \d, \e, \E, \p, \r, \t, and \u.  Again, don't use these if possible.

No newline characters as delimiters are allowed in the following escapes: \A, \B, \Z, \C, and \w.

Finally, the escapes \D, \h, \H, \l, \L, \N, \R, \s, \S, \v, and \x can't use the following characters as delimiters:

  * The digits 0-9.

  * The (single-character) operators +-/*%<>=&:()..

  * The space, tab, and newline characters.

  * All escape sequences except \%, \:, \{, \}, \', \`, \-, \_, \!, \/, \c, \e, and \p.

To have a backslash (actually, the current escape character) appear in the output several escapes are defined: \\, \e or \E.  These are very similar, and only differ with respect to being used in macros or diversions.  See Character Translations, for an exact description of those escapes.

See Implementation Differences, Copy-in Mode, and Diversions, Identifiers, for more information.

Comments
........

Probably one of the most (Unfortunately, this is a lie.  But hopefully future gtroff hackers will believe it :-)) common forms of escapes is the comment.

 -- Escape: \\", , ,
     Start a comment.  Everything to the end of the input line is ignored.

     This may sound simple, but it can be tricky to keep the comments from interfering with the appearance of the final output.

     If the escape is to the right of some text or a request, that portion of the line is ignored, but the space leading up to it is noticed by gtroff.  This only affects the ds and as request and its variants.

     One possibly irritating idiosyncracy is that tabs must not be used to line up comments.  Tabs are not treated as whitespace between the request and macro arguments.

     A comment on a line by itself is treated as a blank line, because after eliminating the comment, that is all that remains:

          Test
          \" comment
          Test

     produces

          Test

          Test

     To avoid this, it is common to start the line with .\", which causes the line to be treated as an undefined request and thus ignored completely.

     Another commenting scheme seen sometimes is three consecutive single quotes (''') at the beginning of a line.  This works, but gtroff gives a warning about an undefined macro (namely ''), which is harmless, but irritating.

 -- Escape: \\#, , ,
     To avoid all this, gtroff has a new comment mechanism using the \# escape.  This escape works the same as \" except that the newline is also ignored:

          Test
          \# comment
          Test

     produces

          Test Test

     as expected.

 -- Request: .ig, [end]
     Ignore all input until gtroff encounters the macro named .END on a line by itself (or .. if END is not specified).  This is useful for commenting out large blocks of text:

          text text text...
          .ig
          This is part of a large block
          of text that has been
          temporarily(?) commented out.

          We can restore it simply by removing
          the .ig request and the ".." at the
          end of the block.
          ..
          More text text text...

     produces

          text text text...  More text text text...

     Note that the commented-out block of text does not cause a break.

     The input is read in copy-mode; auto-incremented registers are affected (see Auto-increment).

Registers
=========

Numeric variables in gtroff are called registers.  There are a number of built-in registers, supplying anything from the date to details of formatting parameters.

See Identifiers, for details on register identifiers.

Setting Registers
-----------------

Define or set registers using the nr request or the \R escape.

Although the following requests and escapes can be used to create registers, simply using an undefined register will cause it to be set to zero.

 -- Request: .nr, ident value
 -- Escape: \\R, ', ident value, '
     Set number register IDENT to VALUE.  If IDENT doesn't exist, gtroff creates it.

     The argument to \R usually has to be enclosed in quotes. See Escapes, for details on parameter delimiting characters.

     The \R escape doesn't produce an input token in gtroff; in other words, it vanishes completely after gtroff has processed it.

     For example, the following two lines are equivalent:

          .nr a (((17 + (3 * 4))) % 4)
          \R'a (((17 + (3 * 4))) % 4)'
              => 1

     Note that the complete transparency of \R can cause surprising effects if you use number registers like .k, which get evaluated at the time they are accessed.

          .ll 1.6i
          .
          aaa bbb ccc ddd eee fff ggg hhh\R':k \n[.k]'
          .tm :k == \n[:k]
              => :k == 126950
          .
          .br
          .
          aaa bbb ccc ddd eee fff ggg hhh\h'0'\R':k \n[.k]'
          .tm :k == \n[:k]
              => :k == 15000

     If you process this with the POSTSCRIPT device (-Tps), there will be a line break eventually after ggg in both input lines.  However, after processing the space after ggg, the partially collected line is not overfull yet, so troff continues to collect input until it sees the space (or in this case, the newline) after hhh.  At this point, the line is longer than the line length, and the line gets broken.

     In the first input line, since the \R escape leaves no traces, the check for the overfull line hasn't been done yet at the point where \R gets handled, and you get a value for the .k number register that is even greater than the current line length.

     In the second input line, the insertion of \h'0' to emit an invisible zero-width space forces troff to check the line length, which in turn causes the start of a new output line.  Now .k returns the expected value.

Both nr and \R have two additional special forms to increment or decrement a register.

 -- Request: .nr, ident +value
 -- Request: .nr, ident -value
 -- Escape: \\R, ', ident +value, '
 -- Escape: \\R, ', ident -value, '
     Increment (decrement) register IDENT by VALUE.

          .nr a 1
          .nr a +1
          \na
              => 2

     To assign the negated value of a register to another register, some care must be taken to get the desired result:

          .nr a 7
          .nr b 3
          .nr a -\nb
          \na
              => 4
          .nr a (-\nb)
          \na
              => -3

     The surrounding parentheses prevent the interpretation of the minus sign as a decrementing operator.  An alternative is to start the assignment with a 0:

          .nr a 7
          .nr b -3
          .nr a \nb
          \na
              => 4
          .nr a 0\nb
          \na
              => -3

 -- Request: .rr, ident
     Remove number register IDENT.  If IDENT doesn't exist, the request is ignored.

 -- Request: .rnn, ident1 ident2
     Rename number register IDENT1 to IDENT2.  If either IDENT1 or IDENT2 doesn't exist, the request is ignored.

 -- Request: .aln, ident1 ident2
     Create an alias IDENT1 for a number register IDENT2.  The new name and the old name are exactly equivalent.  If IDENT1 is undefined, a warning of type reg is generated, and the request is ignored.  See Debugging, for information about warnings.

Interpolating Registers
-----------------------

Numeric registers can be accessed via the \n escape.

 -- Escape: \\n, , i,
 -- Escape: \\n, (, id,
 -- Escape: \\n, [, ident, ]
     Interpolate number register with name IDENT (one-character name I, two-character name ID).  This means that the value of the register is expanded in-place while gtroff is parsing the input line.  Nested assignments (also called indirect assignments) are possible.

          .nr a 5
          .nr as \na+\na
          \n(as
              => 10

          .nr a1 5
          .nr ab 6
          .ds str b
          .ds num 1
          \n[a\n[num]]
              => 5
          \n[a\*[str]]
              => 6

Auto-increment
--------------

Number registers can also be auto-incremented and auto-decremented.  The increment or decrement value can be specified with a third argument to the nr request or \R escape.

 -- Request: .nr, ident value incr
     Set number register IDENT to VALUE; the increment for auto-incrementing is set to INCR.  Note that the \R escape doesn't support this notation.

To activate auto-incrementing, the escape \n has a special syntax form.

 -- Escape: \\n, +, i,
 -- Escape: \\n, -, i,
 -- Escape: \\n, +(, id,
 -- Escape: \\n, -(, id,
 -- Escape: \\n, +[, ident, ]
 -- Escape: \\n, -[, ident, ]
     Before interpolating, increment or decrement IDENT (one-character name I, two-character name ID) by the auto-increment value as specified with the nr request (or the \R escape). If no auto-increment value has been specified, these syntax forms are identical to \n.

For example,

     .nr a 0 1
     .nr xx 0 5
     .nr foo 0 -2
     \n+a, \n+a, \n+a, \n+a, \n+a
     .br
     \n-(xx, \n-(xx, \n-(xx, \n-(xx, \n-(xx
     .br
     \n+[foo], \n+[foo], \n+[foo], \n+[foo], \n+[foo]

produces

     1, 2, 3, 4, 5
     -5, -10, -15, -20, -25
     -2, -4, -6, -8, -10

To change the increment value without changing the value of a register (A in the example), the following can be used:

     .nr a \na 10

Assigning Formats
-----------------

When a register is used, it is always textually replaced (or interpolated) with a representation of that number.  This output format can be changed to a variety of formats (numbers, Roman numerals, etc.). This is done using the af request.

 -- Request: .af, ident format
     Change the output format of a number register.  The first argument IDENT is the name of the number register to be changed, and the second argument FORMAT is the output format.  The following output formats are available:

     1
          Decimal arabic numbers.  This is the default format: 0, 1, 2, 3, ...

     0...0
          Decimal numbers with as many digits as specified.  So, 00 would result in printing numbers as 01, 02, 03, ...

          In fact, any digit instead of zero does work; gtroff only counts how many digits are specified.  As a consequence, af's default format 1 could be specified as 0 also (and exactly this is returned by the \g escape, see below).

     I
          Upper-case Roman numerals: 0, I, II, III, IV, ...

     i
          Lower-case Roman numerals: 0, i, ii, iii, iv, ...

     A
          Upper-case letters: 0, A, B, C, ..., Z, AA, AB, ...

     a
          Lower-case letters: 0, a, b, c, ..., z, aa, ab, ...

     Omitting the number register format causes a warning of type missing.  See Debugging, for more details.  Specifying a nonexistent format causes an error.

     The following example produces 10, X, j, 010:

          .nr a 10
          .af a 1           \" the default format
          \na,
          .af a I
          \na,
          .af a a
          \na,
          .af a 001
          \na

     The largest number representable for the i and I formats is 39999 (or -39999); Unix troff uses z and w to represent 10000 and 5000 in Roman numerals, and so does gtroff.  Currently, the correct glyphs of Roman numeral five thousand and Roman numeral ten thousand (Unicode code points U+2182 and U+2181, respectively) are not available.

     If IDENT doesn't exist, it is created.

     Changing the output format of a read-only register causes an error.  It is necessary to first copy the register's value to a writeable register, then apply the af request to this other register.

 -- Escape: \\g, , i,
 -- Escape: \\g, (, id,
 -- Escape: \\g, [, ident, ]
     Return the current format of the specified register IDENT (one-character name I, two-character name ID).  For example, \ga after the previous example would produce the string 000.  If the register hasn't been defined yet, nothing is returned.

Built-in Registers
------------------

The following lists some built-in registers that are not described elsewhere in this manual.  Any register that begins with a . is read-only.  A complete listing of all built-in registers can be found in Register Index.

\n[.F]
     This string-valued register returns the current input file name.

\n[.H]
     Number of basic units per horizontal unit of output device resolution. See Measurements.

\n[.R]
     The number of number registers available.  This is always 10000 in GNU troff; it exists for backward compatibility.

\n[.U]
     If gtroff is called with the -U command-line option to activate unsafe mode, the number register .U is set to 1, and to zero otherwise.  See Groff Options.

\n[.V]
     Number of basic units per vertical unit of output device resolution. See Measurements.

\n[seconds]
     The number of seconds after the minute, normally in the range 0 to 59, but can be up to 61 to allow for leap seconds. Initialized at start-up of gtroff.

\n[minutes]
     The number of minutes after the hour, in the range 0 to 59. Initialized at start-up of gtroff.

\n[hours]
     The number of hours past midnight, in the range 0 to 23. Initialized at start-up of gtroff.

\n[dw]
     Day of the week (1--7).

\n[dy]
     Day of the month (1--31).

\n[mo]
     Current month (1--12).

\n[year]
     The current year.

\n[yr]
     The current year minus 1900.  Unfortunately, the documentation of Unix Version 7's troff had a year 2000 bug: It incorrectly claimed that yr contains the last two digits of the year.  That claim has never been true of either AT&T troff or GNU troff.  Old troff input that looks like this:

          '\" The following line stopped working after 1999
          This document was formatted in 19\n(yr.

     can be corrected as follows:

          This document was formatted in \n[year].

     or, to be portable to older troff versions, as follows:

          .nr y4 1900+\n(yr
          This document was formatted in \n(y4.

\n[.c]
\n[c.]
     The current input line number.  Register .c is read-only, whereas c. (a gtroff extension) is writable also, affecting both .c and c..

\n[ln]
     The current output line number after a call to the nm request to activate line numbering.

     See Miscellaneous, for more information about line numbering.

\n[.x]
     The major version number.  For example, if the version number is 1.03 then .x contains 1.

\n[.y]
     The minor version number.  For example, if the version number is 1.03 then .y contains 03.

\n[.Y]
     The revision number of groff.

\n[$$]
     The process ID of gtroff.

\n[.g]
     Always 1.  Macros should use this to determine whether they are running under GNU troff.

\n[.A]
     If the command-line option -a is used to produce an ASCII approximation of the output, this is set to 1, zero otherwise.  See Groff Options.

\n[.O]
     This read-only register is set to the suppression nesting level (see escapes \O).  See Suppressing output.

\n[.P]
     This register is set to 1 (and to 0 otherwise) if the current page is actually being printed, i.e., if the -o option is being used to only print selected pages.  See Groff Options, for more information.

\n[.T]
     If gtroff is called with the -T command-line option, the number register .T is set to 1, and zero otherwise. See Groff Options.

\*[.T]
     A single read-write string register that contains the current output device (for example, latin1 or ps).  This is the only string register defined by gtroff.

Manipulating Filling and Adjusting
==================================

Various ways of causing breaks were given in Implicit Line Breaks.  The br request likewise causes a break.  Several other requests also cause breaks, but implicitly.  These are bp, ce, cf, fi, fl, in, nf, rj, sp, ti, and trf.

 -- Request: .br,
     Break the current line, i.e., the input collected so far is emitted without adjustment.

     If the no-break control character is used, gtroff suppresses the break:

          a
          'br
          b
              => a b

Initially, gtroff fills and adjusts text to both margins. Filling can be disabled via the nf request and re-enabled with the fi request.

 -- Request: .fi,
 -- Register: \n[.u]
     Activate fill mode (which is the default).  This request implicitly enables adjusting; it also inserts a break in the text currently being filled.  The read-only number register .u is set to 1.

     The fill mode status is associated with the current environment (see Environments).

     See Line Control, for interaction with the \c escape.

 -- Request: .nf,
     Activate no-fill mode.  Input lines are output as-is, retaining line breaks and ignoring the current line length.  This command implicitly disables adjusting; it also causes a break.  The number register .u is set to 0.

     The fill mode status is associated with the current environment (see Environments).

     See Line Control, for interaction with the \c escape.

 -- Request: .ad, [mode]
 -- Register: \n[.j]
     Set adjusting mode.

     Activation and deactivation of adjusting is done implicitly with calls to the fi or nf requests.

     MODE can have one of the following values:

     l
          Adjust text to the left margin.  This produces what is traditionally called ragged-right text.

     r
          Adjust text to the right margin, producing ragged-left text.

     c
          Center filled text.  This is different to the ce request, which only centers text without filling.

     b
     n
          Justify to both margins.  This is the default used by gtroff.

     Finally, MODE can be the numeric argument returned by the .j register.

     Using ad without argument is the same as saying .ad \[.j].  In particular, gtroff adjusts lines in the same way it did before adjusting was deactivated (with a call to na, say).  For example, this input code

          .de AD
          .  br
          .  ad \\$1
          ..
          .
          .de NA
          .  br
          .  na
          ..
          .
          textA
          .AD r
          .nr ad \n[.j]
          textB
          .AD c
          textC
          .NA
          textD
          .AD         \" back to centering
          textE
          .AD \n[ad]  \" back to right justifying
          textF

     produces the following output:

          textA
                                                              textB
                                    textC
          textD
                                    textE
                                                              textF

     As just demonstrated, the current adjustment mode is available in the read-only number register .j; it can be stored and subsequently used to set adjustment.

     The adjustment mode status is associated with the current environment (see Environments).

 -- Request: .na,
     Disable adjusting.  This request won't change the current adjustment mode: A subsequent call to ad uses the previous adjustment setting.

     The adjustment mode status is associated with the current environment (see Environments).

 -- Request: .brp,
 -- Escape: \\p, , ,
     Break, adjusting the current line per the current adjustment mode.

     With \p, this break will happen at the next word boundary.  The \p itself is removed entirely, adding neither a break nor a space where it appears in input; it can thus be placed in the middle of a word to cause a break at the end of that word.

     In most cases this produces very ugly results since gtroff doesn't have a sophisticated paragraph building algorithm (as TeX has, for example); instead, gtroff fills and adjusts a paragraph line by line:

          This is an uninteresting sentence.
          This is an uninteresting sentence.\p
          This is an uninteresting sentence.

     is formatted as

          This is  an uninteresting  sentence.   This  is an
          uninteresting                            sentence.
          This is an uninteresting sentence.

 -- Request: .ss, word_space_size [sentence_space_size]
 -- Register: \n[.ss]
 -- Register: \n[.sss]
     Change the size of a space between words.  It takes its units as one twelfth of the space width parameter for the current font.  Initially both the WORD_SPACE_SIZE and SENTENCE_SPACE_SIZE are 12.  In fill mode, the values specify the minimum distance.

     If two arguments are given to the ss request, the second argument sets the sentence space size.  If the second argument is not given, sentence space size is set to WORD_SPACE_SIZE.  The sentence space size is used in two circumstances: If the end of a sentence occurs at the end of a line in fill mode, then both an inter-word space and a sentence space are added; if two spaces follow the end of a sentence in the middle of a line, then the second space is a sentence space.  If a second argument is never given to the ss request, the behaviour of Unix troff is the same as that exhibited by GNU troff. In GNU troff, as in Unix troff, a sentence should always be followed by either a newline or two spaces.

     The read-only number registers .ss and .sss hold the values of the parameters set by the first and second arguments of the ss request.

     The word space and sentence space values are associated with the current environment (see Environments).

     Contrary to AT&T troff, this request is not ignored if a TTY output device is used; the given values are then rounded down to a multiple of 12 (see Implementation Differences).

     The request is ignored if there is no parameter.

     Another useful application of the ss request is to insert discardable horizontal space, i.e., space that is discarded at a line break.  For example, paragraph-style footnotes could be separated this way:

          .ll 4.5i
          1.\ This is the first footnote.\c
          .ss 48
          .nop
          .ss 12
          2.\ This is the second footnote.

     The result:

          1. This is the first footnote.        2. This
          is the second footnote.

     Note that the \h escape produces unbreakable space.

 -- Request: .ce, [nnn]
 -- Register: \n[.ce]
     Center text.  While the .ad c request also centers text, it fills the text as well.  ce does not fill the text it affects. This request causes a break.  The number of lines still to be centered is associated with the current environment (see Environments).

     The following example demonstrates the differences.  Here is the input:

          .ll 4i
          .ce 1000
          This is a small text fragment that shows the differences
          between the `.ce' and the `.ad c' request.
          .ce 0

          .ad c
          This is a small text fragment that shows the differences
          between the `.ce' and the `.ad c' request.

     And here the result:

            This is a small text fragment that
                   shows the differences
          between the `.ce' and the `.ad c' request.

            This is a small text fragment that
          shows the differences between the `.ce'
                  and the `.ad c' request.

     With no arguments, ce centers the next line of text.  NNN specifies the number of lines to be centered.  If the argument is zero or negative, centering is disabled.

     The basic length for centering text is the line length (as set with the ll request) minus the indentation (as set with the in request).  Temporary indentation is ignored.

     As can be seen in the previous example, it is a common idiom to turn on centering for a large number of lines, and to turn off centering after text to be centered.  This is useful for any request that takes a number of lines as an argument.

     The .ce read-only number register contains the number of lines remaining to be centered, as set by the ce request.

 -- Request: .rj, [nnn]
 -- Register: \n[.rj]
     Justify unfilled text to the right margin.  Arguments are identical to the ce request.  The .rj read-only number register is the number of lines to be right-justified as set by the rj request. This request causes a break.  The number of lines still to be right-justified is associated with the current environment (see Environments).

Manipulating Hyphenation
========================

Here a description of requests that influence hyphenation.

 -- Request: .hy, [mode]
 -- Register: \n[.hy]
     Enable hyphenation.  The request has an optional numeric argument, MODE, to restrict hyphenation if necessary:

     1
          The default argument if MODE is omitted: hyphenation is enabled, and the first and the last characters of a word are not hyphenated. This is also the start-up value of gtroff.

     2
          Do not hyphenate the last word on a page or column.

     4
          Do not hyphenate the last two characters of a word.

     8
          Do not hyphenate the first two characters of a word.

     16
          Allow hyphenation before the last character of a word.

     32
          Allow hyphenation after the first character of a word.

     The values in the previous table are additive.  For example, value 12 causes gtroff to neither hyphenate the last two nor the first two characters of a word.  Note that value 13 would do exactly the same; in other words, value 1 need not be added if the value is larger than 1.

     Some values cannot be used together because they contradict; for instance, values 4 and 16, and values 8 and 32.

     The number of characters at the beginning of a word after which the first hyphenation point should be inserted is determined by the patterns themselves; it can't be reduced further without introducing additional, invalid hyphenation points (unfortunately, this information is not part of a pattern file, you have to know it in advance).  The same is true for the number of characters at the end of word before the last hyphenation point should be inserted.  For example, the code

          .ll 1
          .hy 48
          splitting

     returns

          s-
          plit-
          t-
          in-
          g

     instead of the correct `split-ting'.  US-English patterns as distributed with groff need two characters at the beginning and three characters at the end; this means that value 4 of hy is mandatory. Value 8 is possible as an additional restriction, but values 1 (the default!), 16, and 32 should be avoided.

     Here is a table of left and right minimum values for hyphenation as needed by the patterns distributed with groff; see the groff_tmac(5) man page (type man groff_tmac at the command line) for more information on groff's language macro files.

     language             pattern name   left min   right min
     Czech                cs             2          2
     US English           us             2          3
     French               fr             2          3
     German traditional   det            2          2
     German reformed      den            2          2
     Swedish              sv             1          2

     Hyphenation exceptions within pattern files (i.e., the words within a \hyphenation group) also obey the hyphenation restrictions given by hy.  However, exceptions specified with the hw do not.

     The current hyphenation restrictions can be found in the read-only number register .hy.

     The hyphenation mode is associated with the current environment (see Environments).

 -- Request: .nh,
     Disable hyphenation (i.e., set the hyphenation mode to zero).  Note that the hyphenation mode of the last call to hy is not remembered.

     The hyphenation mode is associated with the current environment (see Environments).

 -- Request: .hlm, [nnn]
 -- Register: \n[.hlm]
 -- Register: \n[.hlc]
     Set the maximum number of consecutive hyphenated lines to NNN.  If this number is negative, there is no maximum.  The default value is -1 if NNN is omitted.  This value is associated with the current environment (see Environments).  Only lines output from a given environment count towards the maximum associated with that environment.  Hyphens resulting from \% are counted; explicit hyphens are not.

     The current setting of hlm is available in the .hlm read-only number register.  Also the number of immediately preceding consecutive hyphenated lines are available in the read-only number register .hlc.

 -- Request: .hw, word1 word2 ...
     Define how WORD1, WORD2, etc. are to be hyphenated.  The words must be given with hyphens at the hyphenation points.  For example:

          .hw in-sa-lub-rious

     Besides the space character, any character whose hyphenation code value is zero can be used to separate the arguments of hw (see the documentation for the hcode request below for more information). In addition, this request can be used more than once.

     Hyphenation points specified with hw are not subject to the restrictions given by the hy request.

     Hyphenation exceptions specified with the hw request are associated with the current hyphenation language; it causes an error if there is no current hyphenation language.

     This request is ignored if there is no parameter.

     In old versions of troff there was a limited amount of space to store such information; fortunately, with gtroff, this is no longer a restriction.

 -- Escape: \\%, , ,
 -- Escape: \:
     To tell gtroff how to hyphenate words on the fly, use the \% escape, also known as the hyphenation character. Preceding a word with this character prevents it from being hyphenated; putting it inside a word indicates to gtroff that the word may be hyphenated at that point.  Note that this mechanism only affects that one occurrence of the word; to change the hyphenation of a word for the entire document, use the hw request.

     The \: escape inserts a zero-width break point (that is, the word breaks but without adding a hyphen).

          ... check the /var/log/\:httpd/\:access_log file ...

     Note that \X and \Y start a word, that is, the \% escape in (say) \X'...'\%foobar and \Y'...'\%foobar no longer prevents hyphenation but inserts a hyphenation point at the beginning of foobar; most likely this isn't what you want to do.

 -- Request: .hc, [char]
     Change the hyphenation character to CHAR.  This character then works the same as the \% escape, and thus, no longer appears in the output.  Without an argument, hc resets the hyphenation character to be \% (the default) only.

     The hyphenation character is associated with the current environment (see Environments).

 -- Request: .hpf, pattern_file
 -- Request: .hpfa, pattern_file
 -- Request: .hpfcode, a b [c d ...]
     Read in a file of hyphenation patterns.  This file is searched for in the same way as NAME.tmac (or tmac.NAME) is searched for if the -mNAME option is specified.

     It should have the same format as (simple) TeX patterns files.  More specifically, the following scanning rules are implemented.

       * A percent sign starts a comment (up to the end of the line) even if preceded by a backslash.

       * No support for `digraphs' like \$.

       * ^^XX (X is 0--9 or a--f) and ^^X (character code of X in the range 0--127) are recognized; other use of ^ causes an error.

       * No macro expansion.

       * hpf checks for the expression \patterns{...} (possibly with whitespace before and after the braces).  Everything between the braces is taken as hyphenation patterns.  Consequently, { and } are not allowed in patterns.

       * Similarly, \hyphenation{...} gives a list of hyphenation exceptions.

       * \endinput is recognized also.

       * For backwards compatibility, if \patterns is missing, the whole file is treated as a list of hyphenation patterns (only recognizing the % character as the start of a comment).

     If no hpf request is specified (either in the document or in a macro package), gtroff won't hyphenate at all.

     The hpfa request appends a file of patterns to the current list.

     The hpfcode request defines mapping values for character codes in hyphenation patterns.  hpf or hpfa then apply the mapping (after reading the patterns) before replacing or appending them to the current list of patterns.  Its arguments are pairs of character codes -- integers from 0 to 255.  The request maps character code A to code B, code C to code D, and so on.  You can use character codes that would be invalid otherwise.  By default, everything maps to itself except letters `A' to `Z', which map to `a' to `z'.

     The set of hyphenation patterns is associated with the current language set by the hla request.  The hpf request is usually invoked by the troffrc or troffrc-end file; by default, troffrc loads hyphenation patterns and exceptions for American English (in files hyphen.us and hyphenex.us).

     A second call to hpf (for the same language) replaces the hyphenation patterns with the new ones.

     Invoking hpf causes an error if there is no current hyphenation language.

 -- Request: .hcode, c1 code1 [c2 code2 ...]
     Set the hyphenation code of character C1 to CODE1, that of C2 to CODE2, etc.  A hyphenation code must be a single input character (not a special character) other than a digit or a space.

     To make hyphenation work, hyphenation codes must be set up.  At start-up, groff only assigns hyphenation codes to the letters a--z (mapped to themselves) and to the letters A--Z (mapped to a--z); all other hyphenation codes are set to zero.  Normally, hyphenation patterns contain only lowercase letters, which should be applied regardless of case.  In other words, the words `FOO' and `Foo' should be hyphenated exactly the same way as the word `foo' is hyphenated, and this is what hcode is good for.  Words that contain other letters won't be hyphenated properly if the corresponding hyphenation patterns actually do contain them.  For example, the following hcode requests are necessary to assign hyphenation codes to the letters ÄäÖöÜüß (this is needed for German):

          .hcode ä ä  Ä ä
          .hcode ö ö  Ö ö
          .hcode ü ü  Ü ü
          .hcode ß ß

     Without those assignments, groff treats German words like `Kindergärten' (the plural form of `kindergarten') as two substrings `kinderg' and `rten' because the hyphenation code of the umlaut a is zero by default.  There is a German hyphenation pattern that covers `kinder', so groff finds the hyphenation `kin-der'. The other two hyphenation points (`kin-der-gär-ten') are missed.

     This request is ignored if it has no parameter.

 -- Request: .hym, [length]
 -- Register: \n[.hym]
     Set the (right) hyphenation margin to LENGTH.  If the current adjustment mode is not b or n, the line is not hyphenated if it is shorter than LENGTH.  Without an argument, the hyphenation margin is reset to its default value, which is 0.  The default scaling indicator for this request is m.  The hyphenation margin is associated with the current environment (see Environments).

     A negative argument resets the hyphenation margin to zero, emitting a warning of type range.

     The current hyphenation margin is available in the .hym read-only number register.

 -- Request: .hys, [hyphenation_space]
 -- Register: \n[.hys]
     Set the hyphenation space to HYPHENATION_SPACE.  If the current adjustment mode is b or n, don't hyphenate the line if it can be justified by adding no more than HYPHENATION_SPACE extra space to each word space.  Without argument, the hyphenation space is set to its default value, which is 0.  The default scaling indicator for this request is m.  The hyphenation space is associated with the current environment (see Environments).

     A negative argument resets the hyphenation space to zero, emitting a warning of type range.

     The current hyphenation space is available in the .hys read-only number register.

 -- Request: .shc, [glyph]
     Set the soft hyphen character to GLYPH. (Soft hyphen character is a misnomer since it is an output glyph.)  If the argument is omitted, the soft hyphen character is set to the default glyph \(hy (this is the start-up value of gtroff also). The soft hyphen character is the glyph that is inserted when a word is hyphenated at a line break.  If the soft hyphen character does not exist in the font of the character immediately preceding a potential break point, then the line is not broken at that point.  Neither definitions (specified with the char request) nor translations (specified with the tr request) are considered when finding the soft hyphen character.

 -- Request: .hla, language
 -- Register: \n[.hla]
     Set the current hyphenation language to the string LANGUAGE. Hyphenation exceptions specified with the hw request and hyphenation patterns specified with the hpf and hpfa requests are both associated with the current hyphenation language.  The hla request is usually invoked by the troffrc or the troffrc-end files; troffrc sets the default language to us.

     The current hyphenation language is available as a string in the read-only number register .hla.

          .ds curr_language \n[.hla]
          \*[curr_language]
              => us

Manipulating Spacing
====================

 -- Request: .sp, [distance]
     Space downwards DISTANCE.  With no argument it advances 1 line.  A negative argument causes gtroff to move up the page the specified distance.  If the argument is preceded by a | then gtroff moves that distance from the top of the page.  This request causes a line break, and that adds the current line spacing to the space you have just specified.  The default scaling indicator is v.

     For convenience you may wish to use the following macros to set the height of the next line at a given distance from the top or the bottom of the page:

          .de y-from-top-down
          .  sp |\\$1-\\n[.v]u
          ..
          .
          .de y-from-bot-up
          .  sp |\\n[.p]u-\\$1-\\n[.v]u
          ..

     A call to .y-from-bot-up 10c means that the bottom of the next line will be at 10 cm from the paper edge at the bottom.

     If a vertical trap is sprung during execution of sp, the amount of vertical space after the trap is discarded.  For example, this

          .de xxx
          ..
          .
          .wh 0 xxx
          .
          .pl 5v
          foo
          .sp 2
          bar
          .sp 50
          baz

     results in

          foo

          bar

          baz

     The amount of discarded space is available in the number register .trunc.

     To protect sp against vertical traps, use the vpt request:

          .vpt 0
          .sp -3
          .vpt 1

 -- Request: .ls, [nnn]
 -- Register: \n[.L]
     Output NNN-1 blank lines after each line of text.  With no argument, gtroff uses the previous value before the last ls call.

          .ls 2    \" This causes double-spaced output
          .ls 3    \" This causes triple-spaced output
          .ls      \" Again double-spaced

     The line spacing is associated with the current environment (see Environments).

     The read-only number register .L contains the current line spacing setting.

See Changing Type Sizes, for the requests vs and pvs as alternatives to ls.

 -- Escape: \\x, ', spacing, '
 -- Register: \n[.a]
     Sometimes, extra vertical spacing is only needed occasionally, e.g. to allow space for a tall construct (like an equation).  The \x escape does this.  The escape is given a numerical argument, usually enclosed in quotes (like \x'3p'); the default scaling indicator is v.  If this number is positive extra vertical space is inserted below the current line.  A negative number adds space above. If this escape is used multiple times on the same line, the maximum of the values is used.

     See Escapes, for details on parameter delimiting characters.

     The .a read-only number register contains the most recent (non-negative) extra vertical line space.

     Using \x can be necessary in combination with the \b escape, as the following example shows.

          This is a test with the \[rs]b escape.
          .br
          This is a test with the \[rs]b escape.
          .br
          This is a test with \b'xyz'\x'-1m'\x'1m'.
          .br
          This is a test with the \[rs]b escape.
          .br
          This is a test with the \[rs]b escape.

     produces

          This is a test with the \b escape.
          This is a test with the \b escape.
                              x
          This is a test with y.
                              z
          This is a test with the \b escape.
          This is a test with the \b escape.

 -- Request: .ns,
 -- Request: .rs,
 -- Register: \n[.ns]
     Enable no-space mode.  In this mode, spacing (either via sp or via blank lines) is disabled.  The bp request to advance to the next page is also disabled, except if it is accompanied by a page number (see Page Control, for more information).  This mode ends when actual text is output or the rs request is encountered, which ends no-space mode.  The read-only number register .ns is set to 1 as long as no-space mode is active.

     This request is useful for macros that conditionally insert vertical space before the text starts (for example, a paragraph macro could insert some space except when it is the first paragraph after a section header).

Tabs and Fields
===============

A tab character (ASCII char 9, EBCDIC char 5) causes a horizontal movement to the next tab stop (much like it did on a typewriter).

 -- Escape: \\t, , ,
     This escape is a non-interpreted tab character.  In copy mode (see Copy-in Mode), \t is the same as a real tab character.

 -- Request: .ta, [n1 n2 ... nn T r1 r2 ... rn]
 -- Register: \n[.tabs]
     Change tab stop positions.  This request takes a series of tab specifiers as arguments (optionally divided into two groups with the letter T) that indicate where each tab stop is to be (overriding any previous settings).

     Tab stops can be specified absolutely, i.e., as the distance from the left margin.  For example, the following sets 6 tab stops every one inch.

          .ta 1i 2i 3i 4i 5i 6i

     Tab stops can also be specified using a leading +, which means that the specified tab stop is set relative to the previous tab stop. For example, the following is equivalent to the previous example.

          .ta 1i +1i +1i +1i +1i +1i

     gtroff supports an extended syntax to specify repeat values after the T mark (these values are always taken as relative) -- this is the usual way to specify tabs set at equal intervals.  The following is, yet again, the same as the previous examples.  It does even more since it defines an infinite number of tab stops separated by one inch.

          .ta T 1i

     Now we are ready to interpret the full syntax given at the beginning: Set tabs at positions N1, N2, ..., NN and then set tabs at NN+R1, NN+R2, ..., NN+RN and then at NN+RN+R1, NN+RN+R2, ..., NN+RN+RN, and so on.

     Example: 4c +6c T 3c 5c 2c is equivalent to 4c 10c 13c 18c 20c 23c 28c 30c ....

     The material in each tab column (i.e., the column between two tab stops) may be justified to the right or left or centered in the column.  This is specified by appending R, L, or C to the tab specifier.  The default justification is L.  Example:

          .ta 1i 2iC 3iR

     Some notes:

       * The default unit of the ta request is m.

       * A tab stop is converted into a non-breakable horizontal movement that can be neither stretched nor squeezed.  For example,

               .ds foo a\tb\tc
               .ta T 5i
               \*[foo]

          creates a single line, which is a bit longer than 10 inches (a string is used to show exactly where the tab characters are).  Now consider the following:

               .ds bar a\tb b\tc
               .ta T 5i
               \*[bar]

          gtroff first converts the tab stops of the line into unbreakable horizontal movements, then splits the line after the second b (assuming a sufficiently short line length).  Usually, this isn't what the user wants.

       * Superfluous tabs (i.e., tab characters that do not correspond to a tab stop) are ignored except the first one, which delimits the characters belonging to the last tab stop for right-justifying or centering. Consider the following example

               .ds Z   foo\tbar\tfoo
               .ds ZZ  foo\tbar\tfoobar
               .ds ZZZ foo\tbar\tfoo\tbar
               .ta 2i 4iR
               \*[Z]
               .br
               \*[ZZ]
               .br
               \*[ZZZ]
               .br

          which produces the following output:

               foo                 bar              foo
               foo                 bar           foobar
               foo                 bar              foobar

          The first line right-justifies the second `foo' relative to the tab stop.  The second line right-justifies `foobar'.  The third line finally right-justifies only `foo' because of the additional tab character, which marks the end of the string belonging to the last defined tab stop.

       * Tab stops are associated with the current environment (see Environments).

       * Calling ta without an argument removes all tab stops.

       * The start-up value of gtroff is T 0.5i.

     The read-only number register .tabs contains a string representation of the current tab settings suitable for use as an argument to the ta request.

          .ds tab-string \n[.tabs]
          \*[tab-string]
              => T120u

     The troff version of the Plan 9 operating system uses register .S for the same purpose.

 -- Request: .tc, [fill-glyph]
     Normally gtroff fills the space to the next tab stop with whitespace.  This can be changed with the tc request.  With no argument gtroff reverts to using whitespace, which is the default.  The value of this tab repetition character is associated with the current environment (see Environments). (Tab repetition character is a misnomer since it is an output glyph.)

 -- Request: .linetabs, n
 -- Register: \n[.linetabs]
     If N is missing or not zero, enable line-tabs mode, or disable it otherwise (the default).  In line-tabs mode, gtroff computes tab distances relative to the (current) output line instead of the input line.

     For example, the following code:

          .ds x a\t\c
          .ds y b\t\c
          .ds z c
          .ta 1i 3i
          \*x
          \*y
          \*z

     in normal mode, results in the output

          a         b         c

     in line-tabs mode, the same code outputs

          a         b                   c

     Line-tabs mode is associated with the current environment.  The read-only register .linetabs is set to 1 if in line-tabs mode, and 0 in normal mode.

Leaders
-------

Sometimes it may be desirable to use the tc request to fill a particular tab stop with a given glyph (for example dots in a table of contents), but also normal tab stops on the rest of the line. For this gtroff provides an alternate tab mechanism, called leaders, which does just that.

A leader character (character code 1) behaves similarly to a tab character: It moves to the next tab stop.  The only difference is that for this movement, the fill glyph defaults to a period character and not to space.

 -- Escape: \\a, , ,
     This escape is a non-interpreted leader character.  In copy mode (see Copy-in Mode), \a is the same as a real leader character.

 -- Request: .lc, [fill-glyph]
     Declare the leader repetition character. (Leader repetition character is a misnomer since it is an output glyph.) Without an argument, leaders act the same as tabs (i.e., using whitespace for filling).  gtroff's start-up value is a dot (.).  The value of the leader repetition character is associated with the current environment (see Environments).

For a table of contents, to name an example, tab stops may be defined so that the section number is one tab stop, the title is the second with the remaining space being filled with a line of dots, and then the page number slightly separated from the dots.

     .ds entry 1.1\tFoo\a\t12
     .lc .
     .ta 1i 5i +.25i
     \*[entry]

This produces

     1.1  Foo..........................................  12

Fields
------

Fields are a more general way of laying out tabular data.  A field is defined as the data between a pair of delimiting characters. It contains substrings that are separated by padding characters. The width of a field is the distance on the input line from the position where the field starts to the next tab stop.  A padding character inserts stretchable space similar to TeX's \hss command (thus it can even be negative) to make the sum of all substring lengths plus the stretchable space equal to the field width.  If more than one padding character is inserted, the available space is evenly distributed among them.

 -- Request: .fc, [delim-char [padding-char]]
     Define a delimiting and a padding character for fields.  If the latter is missing, the padding character defaults to a space character.  If there is no argument at all, the field mechanism is disabled (which is the default).  Note that contrary to e.g. the tab repetition character, delimiting and padding characters are not associated to the current environment (see Environments).

     Example:

          .fc # ^
          .ta T 3i
          #foo^bar^smurf#
          .br
          #foo^^bar^smurf#

     and here the result:

          foo         bar          smurf
          foo            bar       smurf

Character Translations
======================

The control character (.) and the no-break control character (') can be changed with the cc and c2 requests, respectively.

 -- Request: .cc, [c]
     Set the control character to C.  With no argument the default control character . is restored.  The value of the control character is associated with the current environment (see Environments).

 -- Request: .c2, [c]
     Set the no-break control character to C.  With no argument the default control character ' is restored.  The value of the no-break control character is associated with the current environment (see Environments).

See Requests.

 -- Request: .eo,
     Disable the escape mechanism completely.  After executing this request, the backslash character \ no longer starts an escape sequence.

     This request can be very helpful in writing macros since it is not necessary then to double the escape character.  Here an example:

          .\" This is a simplified version of the
          .\" .BR request from the man macro package
          .eo
          .de BR
          .  ds result \&
          .  while (\n[.$] >= 2) \{\
          .    as result \fB\$1\fR\$2
          .    shift 2
          .  \}
          .  if \n[.$] .as result \fB\$1
          \*[result]
          .  ft R
          ..
          .ec

 -- Request: .ec, [c]
     Set the escape character to C.  With no argument the default escape character \ is restored.  It can be also used to re-enable the escape mechanism after an eo request.

     Note that changing the escape character globally likely breaks macro packages since gtroff has no mechanism to `intern' macros, i.e., to convert a macro definition into an internal form that is independent of its representation (TeX has this mechanism).  If a macro is called, it is executed literally.

 -- Request: .ecs,
 -- Request: .ecr,
     The ecs request saves the current escape character in an internal register.  Use this request in combination with the ec request to temporarily change the escape character.

     The ecr request restores the escape character saved with ecs.  Without a previous call to ecs, this request sets the escape character to \.

 -- Escape: \\\\, , ,
 -- Escape: \\e, , ,
 -- Escape: \\E, , ,
     Print the current escape character (which is the backslash character \ by default).

     \\ is a `delayed' backslash; more precisely, it is the default escape character followed by a backslash, which no longer has special meaning due to the leading escape character.  It is not an escape sequence in the usual sense!  In any unknown escape sequence \X the escape character is ignored and X is printed. But if X is equal to the current escape character, no warning is emitted.

     As a consequence, only at top-level or in a diversion a backslash glyph is printed; in copy-in mode, it expands to a single backslash, which then combines with the following character to an escape sequence.

     The \E escape differs from \e by printing an escape character that is not interpreted in copy mode.  Use this to define strings with escapes that work when used in copy mode (for example, as a macro argument).  The following example defines strings to begin and end a superscript:

          .ds { \v'-.3m'\s'\En[.s]*60/100'
          .ds } \s0\v'.3m'

     Another example to demonstrate the differences between the various escape sequences, using a strange escape character, -.

          .ec -
          .de xxx
          --A'foo'
          ..
          .xxx
              => -A'foo'

     The result is surprising for most users, expecting 1 since foo is a valid identifier.  What has happened?  As mentioned above, the leading escape character makes the following character ordinary.  Written with the default escape character the sequence -- becomes \- -- this is the minus sign.

     If the escape character followed by itself is a valid escape sequence, only \E yields the expected result:

          .ec -
          .de xxx
          -EA'foo'
          ..
          .xxx
              => 1

 -- Escape: \\., , ,
     Similar to \\, the sequence \. isn't a real escape sequence.  As before, a warning message is suppressed if the escape character is followed by a dot, and the dot itself is printed.

          .de foo
          .  nop foo
          .
          .  de bar
          .    nop bar
          \\..
          .
          ..
          .foo
          .bar
              => foo bar

     The first backslash is consumed while the macro is read, and the second is swallowed while executing macro foo.

A translation is a mapping of an input character to an output glyph.  The mapping occurs at output time, i.e., the input character gets assigned the metric information of the mapped output character right before input tokens are converted to nodes (see Gtroff Internals, for more on this process).

 -- Request: .tr, abcd...
 -- Request: .trin, abcd...
     Translate character A to glyph B, character C to glyph D, etc.  If there is an odd number of arguments, the last one is translated to an unstretchable space (\ ).

     The trin request is identical to tr, but when you unformat a diversion with asciify it ignores the translation. See Diversions, for details about the asciify request.

     Some notes:

       * Special characters (\(XX, \[XXX], \C'XXX', \', \`, \-, \_), glyphs defined with the char request, and numbered glyphs (\N'XXX') can be translated also.

       * The \e escape can be translated also.

       * Characters can be mapped onto the \% and \~ escapes (but \% and \~ can't be mapped onto another glyph).

       * The following characters can't be translated: space (with one exception, see below), backspace, newline, leader (and \a), tab (and \t).

       * Translations are not considered for finding the soft hyphen character set with the shc request.

       * The pair C\& (this is an arbitrary character C followed by the zero width space character) maps this character to nothing.

               .tr a\&
               foo bar
                   => foo br

          It is even possible to map the space character to nothing:

               .tr aa \&
               foo bar
                   => foobar

          As shown in the example, the space character can't be the first character/glyph pair as an argument of tr.  Additionally, it is not possible to map the space character to any other glyph; requests like .tr aa x undo .tr aa \& instead.

          If justification is active, lines are justified in spite of the `empty' space character (but there is no minimal distance, i.e. the space character, between words).

       * After an output glyph has been constructed (this happens at the moment immediately before the glyph is appended to an output glyph list, either by direct output, in a macro, diversion, or string), it is no longer affected by tr.

       * Translating character to glyphs where one of them or both are undefined is possible also; tr does not check whether the entities in its argument do exist.

          See Gtroff Internals.

       * troff no longer has a hard-coded dependency on Latin-1; all charXXX entities have been removed from the font description files.  This has a notable consequence that shows up in warnings like can't find character with input code XXX if the tr request isn't handled properly.

          Consider the following translation:

               .tr éÉ

          This maps input character é onto glyph É, which is identical to glyph char201.  But this glyph intentionally doesn't exist!  Instead, \[char201] is treated as an input character entity and is by default mapped onto \['E], and gtroff doesn't handle translations of translations.

          The right way to write the above translation is

               .tr é\['E]

          In other words, the first argument of tr should be an input character or entity, and the second one a glyph entity.

       * Without an argument, the tr request is ignored.

 -- Request: .trnt, abcd...
     trnt is the same as the tr request except that the translations do not apply to text that is transparently throughput into a diversion with \!.  See Diversions, for more information.

     For example,

          .tr ab
          .di x
          \!.tm a
          .di
          .x

     prints b to the standard error stream; if trnt is used instead of tr it prints a.

Troff and Nroff Mode
====================

Originally, nroff and troff were two separate programs, the former for TTY output, the latter for everything else.  With GNU troff, both programs are merged into one executable, sending its output to a device driver (grotty for TTY devices, grops for POSTSCRIPT, etc.) which interprets the intermediate output of gtroff.  For Unix troff it makes sense to talk about Nroff mode and Troff mode since the differences are hardcoded.  For GNU troff, this distinction is not appropriate because gtroff simply takes the information given in the font files for a particular device without handling requests specially if a TTY output device is used.

Usually, a macro package can be used with all output devices. Nevertheless, it is sometimes necessary to make a distinction between TTY and non-TTY devices: gtroff provides two built-in conditions n and t for the if, ie, and while requests to decide whether gtroff shall behave like nroff or like troff.

 -- Request: .troff,
     Make the t built-in condition true (and the n built-in condition false) for if, ie, and while conditional requests.  This is the default if gtroff (not groff) is started with the -R switch to avoid loading of the start-up files troffrc and troffrc-end.  Without -R, gtroff stays in troff mode if the output device is not a TTY (e.g. `ps').

 -- Request: .nroff,
     Make the n built-in condition true (and the t built-in condition false) for if, ie, and while conditional requests.  This is the default if gtroff uses a TTY output device; the code for switching to nroff mode is in the file tty.tmac, which is loaded by the start-up file troffrc.

See Conditionals and Loops, for more details on built-in conditions.

Line Layout
===========

The following drawing shows the dimensions that gtroff uses for placing a line of output onto the page.  They are labeled with the request that manipulates each dimension.

          -->| in |<--
             |<-----------ll------------>|
        +----+----+----------------------+----+
        |    :    :                      :    |
        +----+----+----------------------+----+
     -->| po |<--
        |<--------paper width---------------->|

These dimensions are:

po
     Page offset -- this is the leftmost position of text on the final output, defining the left margin.

in
     Indentation -- this is the distance from the left margin where text is printed.

ll
     Line length -- this is the distance from the left margin to right margin.

A simple demonstration:

     .ll 3i
     This is text without indentation.
     The line length has been set to 3\~inch.
     .in +.5i
     .ll -.5i
     Now the left and right margins are both increased.
     .in
     .ll
     Calling .in and .ll without parameters restore
     the previous values.

Result:

     This  is text without indenta-
     tion.   The  line  length  has
     been set to 3 inch.
          Now   the  left  and
          right  margins   are
          both increased.
     Calling  .in  and  .ll without
     parameters restore the  previ-
     ous values.

 -- Request: .po, [offset]
 -- Request: .po, +offset
 -- Request: .po, -offset
 -- Register: \n[.o]
     Set horizontal page offset to OFFSET (or increment or decrement the current value by OFFSET).  Note that this request does not cause a break, so changing the page offset in the middle of text being filled may not yield the expected result.  The initial value is 1i.  For TTY output devices, it is set to 0 in the startup file troffrc; the default scaling indicator is m (and not v as incorrectly documented in the original Unix troff manual).

     The current page offset can be found in the read-only number register .o.

     If po is called without an argument, the page offset is reset to the previous value before the last call to po.

          .po 3i
          \n[.o]
              => 720
          .po -1i
          \n[.o]
              => 480
          .po
          \n[.o]
              => 720

 -- Request: .in, [indent]
 -- Request: .in, +indent
 -- Request: .in, -indent
 -- Register: \n[.i]
     Set indentation to INDENT (or increment or decrement the current value by INDENT).  This request causes a break.  Initially, there is no indentation.

     If in is called without an argument, the indentation is reset to the previous value before the last call to in.  The default scaling indicator is m.

     The indentation is associated with the current environment (see Environments).

     If a negative indentation value is specified (which is not allowed), gtroff emits a warning of type range and sets the indentation to zero.

     The effect of in is delayed until a partially collected line (if it exists) is output.  A temporary indentation value is reset to zero also.

     The current indentation (as set by in) can be found in the read-only number register .i.

 -- Request: .ti, offset
 -- Request: .ti, +offset
 -- Request: .ti, -offset
 -- Register: \n[.in]
     Temporarily indent the next output line by OFFSET.  If an increment or decrement value is specified, adjust the temporary indentation relative to the value set by the in request.

     This request causes a break; its value is associated with the current environment (see Environments).  The default scaling indicator is m.  A call of ti without an argument is ignored.

     If the total indentation value is negative (which is not allowed), gtroff emits a warning of type range and sets the temporary indentation to zero.  `Total indentation' is either OFFSET if specified as an absolute value, or the temporary plus normal indentation, if OFFSET is given as a relative value.

     The effect of ti is delayed until a partially collected line (if it exists) is output.

     The read-only number register .in is the indentation that applies to the current output line.

     The difference between .i and .in is that the latter takes into account whether a partially collected line still uses the old indentation value or a temporary indentation value is active.

 -- Request: .ll, [length]
 -- Request: .ll, +length
 -- Request: .ll, -length
 -- Register: \n[.l]
 -- Register: \n[.ll]
     Set the line length to LENGTH (or increment or decrement the current value by LENGTH).  Initially, the line length is set to 6.5i.  The effect of ll is delayed until a partially collected line (if it exists) is output.  The default scaling indicator is m.

     If ll is called without an argument, the line length is reset to the previous value before the last call to ll.  If a negative line length is specified (which is not allowed), gtroff emits a warning of type range and sets the line length to zero.

     The line length is associated with the current environment (see Environments).

     The current line length (as set by ll) can be found in the read-only number register .l.  The read-only number register .ll is the line length that applies to the current output line.

     Similar to .i and .in, the difference between .l and .ll is that the latter takes into account whether a partially collected line still uses the old line length value.

Line Control
============

It is important to understand how gtroff handles input and output lines.

Many escapes use positioning relative to the input line.  For example, this

     This is a \h'|1.2i'test.

     This is a
     \h'|1.2i'test.

produces

     This is a   test.

     This is a             test.

The main usage of this feature is to define macros that act exactly at the place where called.

     .\" A simple macro to underline a word
     .de underline
     .  nop \\$1\l'|0\[ul]'
     ..

In the above example, |0 specifies a negative distance from the current position (at the end of the just emitted argument \$1) back to the beginning of the input line.  Thus, the \l escape draws a line from right to left.

gtroff makes a difference between input and output line continuation; the latter is also called interrupting a line.

 -- Escape: \\RET, , ,
 -- Escape: \\c, , ,
 -- Register: \n[.int]
     Continue a line.  \RET (this is a backslash at the end of a line immediately followed by a newline) works on the input level, suppressing the effects of the following newline in the input.

          This is a \
          .test
              => This is a .test

     The | operator is also affected.

     \c works on the output level.  Anything after this escape on the same line is ignored except \R, which works as usual.  Anything before \c on the same line is appended to the current partial output line.  The next non-command line after an interrupted line counts as a new input line.

     The visual results depend on whether no-fill mode is active.

       * If no-fill mode is active (using the nf request), the next input text line after \c is handled as a continuation of the same input text line.

               .nf
               This is a \c
               test.
                   => This is a test.

       * If fill mode is active (using the fi request), a word interrupted with \c is continued with the text on the next input text line, without an intervening space.

               This is a te\c
               st.
                   => This is a test.

     Note that an intervening control line that causes a break is stronger than \c, flushing out the current partial line in the usual way.

     The .int register contains a positive value if the last output line was interrupted with \c; this is associated with the current environment (see Environments).

Page Layout
===========

gtroff provides some very primitive operations for controlling page layout.

 -- Request: .pl, [length]
 -- Request: .pl, +length
 -- Request: .pl, -length
 -- Register: \n[.p]
     Set the page length to LENGTH (or increment or decrement the current value by LENGTH).  This is the length of the physical output page.  The default scaling indicator is v.

     The current setting can be found in the read-only number register .p.

     Note that this only specifies the size of the page, not the top and bottom margins.  Those are not set by gtroff directly. See Traps, for further information on how to do this.

     Negative pl values are possible also, but not very useful: No trap is sprung, and each line is output on a single page (thus suppressing all vertical spacing).

     If no argument or an invalid argument is given, pl sets the page length to 11i.

gtroff provides several operations that help in setting up top and bottom titles (or headers and footers).

 -- Request: .tl, 'left'center'right'
     Print a title line.  It consists of three parts: a left justified portion, a centered portion, and a right justified portion.  The argument separator ' can be replaced with any character not occurring in the title line.  The % character is replaced with the current page number.  This character can be changed with the pc request (see below).

     Without argument, tl is ignored.

     Some notes:

       * The line length set by the ll request is not honoured by tl; use the lt request (described below) instead, to control line length for text set by tl.

       * A title line is not restricted to the top or bottom of a page.

       * tl prints the title line immediately, ignoring a partially filled line (which stays untouched).

       * It is not an error to omit closing delimiters.  For example, .tl /foo is equivalent to .tl /foo///: It prints a title line with the left justified word foo; the centered and right justified parts are empty.

       * tl accepts the same parameter delimiting characters as the \A escape; see Escapes.

 -- Request: .lt, [length]
 -- Request: .lt, +length
 -- Request: .lt, -length
 -- Register: \n[.lt]
     The title line is printed using its own line length, which is specified (or incremented or decremented) with the lt request.  Initially, the title line length is set to 6.5i.  If a negative line length is specified (which is not allowed), gtroff emits a warning of type range and sets the title line length to zero.  The default scaling indicator is m.  If lt is called without an argument, the title length is reset to the previous value before the last call to lt.

     The current setting of this is available in the .lt read-only number register; it is associated with the current environment (see Environments).

 -- Request: .pn, page
 -- Request: .pn, +page
 -- Request: .pn, -page
 -- Register: \n[.pn]
     Change (increase or decrease) the page number of the next page. The only argument is the page number; the request is ignored without a parameter.

     The read-only number register .pn contains the number of the next page: either the value set by a pn request, or the number of the current page plus 1.

 -- Request: .pc, [char]
     Change the page number character (used by the tl request) to a different character.  With no argument, this mechanism is disabled. Note that this doesn't affect the number register %.

See Traps.

Page Control
============

 -- Request: .bp, [page]
 -- Request: .bp, +page
 -- Request: .bp, -page
 -- Register: \n[%]
     Stop processing the current page and move to the next page.  This request causes a break.  It can also take an argument to set (increase, decrease) the page number of the next page (which actually becomes the current page after bp has finished).  The difference between bp and pn is that pn does not cause a break or actually eject a page.  See Page Layout.

          .de newpage                         \" define macro
          'bp                                 \" begin page
          'sp .5i                             \" vertical space
          .tl 'left top'center top'right top' \" title
          'sp .3i                             \" vertical space
          ..                                  \" end macro

     bp has no effect if not called within the top-level diversion (see Diversions).

     The read-write register % holds the current page number.

     The number register .pe is set to 1 while bp is active.  See Page Location Traps.

 -- Request: .ne, [space]
     It is often necessary to force a certain amount of space before a new page occurs.  This is most useful to make sure that there is not a single orphan line left at the bottom of a page.  The ne request ensures that there is a certain distance, specified by the first argument, before the next page is triggered (see Traps, for further information).  The default scaling indicator for ne is v; the default value of SPACE is 1v if no argument is given.

     For example, to make sure that no fewer than 2 lines get orphaned, do the following before each paragraph:

          .ne 2
          text text text

     ne then automatically causes a page break if there is space for one line only.

 -- Request: .sv, [space]
 -- Request: .os,
     sv is similar to the ne request; it reserves the specified amount of vertical space.  If the desired amount of space exists before the next trap (or the bottom page boundary if no trap is set), the space is output immediately (ignoring a partially filled line, which stays untouched).  If there is not enough space, it is stored for later output via the os request.  The default value is 1v if no argument is given; the default scaling indicator is v.

     Both sv and os ignore no-space mode.  While the sv request allows negative values for SPACE, os ignores them.

 -- Register: \n[nl]
     This register contains the current vertical position.  If the vertical position is zero and the top of page transition hasn't happened yet, nl is set to negative value.  gtroff itself does this at the very beginning of a document before anything has been printed, but the main usage is to plant a header trap on a page if this page has already started.

     Consider the following:

          .de xxx
          .  sp
          .  tl ''Header''
          .  sp
          ..
          .
          First page.
          .bp
          .wh 0 xxx
          .nr nl (-1)
          Second page.

     Result:

          First page.

          ...

                                       Header

          Second page.

          ...

     Without resetting nl to a negative value, the just planted trap would be active beginning with the next page, not the current one.

     See Diversions, for a comparison with the .h and .d registers.

Fonts and Symbols
=================

gtroff can switch fonts at any point in the text.

The basic set of fonts is R, I, B, and BI. These are Times Roman, Italic, Bold, and Bold Italic.  For non-TTY devices, there is also at least one symbol font that contains various special symbols (Greek, mathematics).

Changing Fonts
--------------

 -- Request: .ft, [font]
 -- Escape: \\f, , f,
 -- Escape: \\f, (, fn,
 -- Escape: \\f, [, font, ]
 -- Register: \n[.sty]
     The ft request and the \f escape change the current font to FONT (one-character name F, two-character name FN).

     If FONT is a style name (as set with the sty request or with the styles command in the DESC file), use it within the current font family (as set with the fam request, the \F escape, or the family command in the DESC file).

     It is not possible to switch to a font with the name DESC (whereas this name could be used as a style name; however, this is not recommended).

     With no argument or using P as an argument, .ft switches to the previous font.  Use \f[] to do this with the escape.  The old syntax forms \fP or \f[P] are also supported.

     Fonts are generally specified as upper-case strings, which are usually 1 to 4 characters representing an abbreviation or acronym of the font name.  This is no limitation, just a convention.

     The example below produces two identical lines.

          eggs, bacon,
          .ft B
          spam
          .ft
          and sausage.

          eggs, bacon, \fBspam\fP and sausage.

     Note that \f doesn't produce an input token in gtroff.  As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font on the fly:

          .mc \f[I]x\f[]

     The current style name is available in the read-only number register .sty (this is a string-valued register); if the current font isn't a style, the empty string is returned.  It is associated with the current environment.

     See Font Positions, for an alternative syntax.

 -- Request: .ftr, f [g]
     Translate font F to font G.  Whenever a font named F is referred to in a \f escape sequence, in the F and S conditional operators, or in the ft, ul, bd, cs, tkf, special, fspecial, fp, or sty requests, font G is used.  If G is missing or equal to F the translation is undone.

     Note that it is not possible to chain font translations.  Example:

          .ftr XXX TR
          .ftr XXX YYY
          .ft XXX
              => warning: can't find font `XXX'

 -- Request: .fzoom, f [zoom]
 -- Register: \n[.zoom]
     Set magnification of font F to factor ZOOM, which must be a non-negative integer multiple of 1/1000th.  This request is useful to adjust the optical size of a font in relation to the others.  In the example below, font CR is magnified by 10% (the zoom factor is thus 1.1).

          .fam P
          .fzoom CR 1100
          .ps 12
          Palatino and \f[CR]Courier\f[]

     A missing or zero value of ZOOM is the same as a value of 1000, which means no magnification.  F must be a real font name, not a style.

     Note that the magnification of a font is completely transparent to troff; a change of the zoom factor doesn't cause any effect except that the dimensions of glyphs, (word) spaces, kerns, etc., of the affected font are adjusted accordingly.

     The zoom factor of the current font is available in the read-only number register .zoom, in multiples of 1/1000th.  It returns zero if there is no magnification.

Font Families
-------------

Due to the variety of fonts available, gtroff has added the concept of font families and font styles.  The fonts are specified as the concatenation of the font family and style.  Specifying a font without the family part causes gtroff to use that style of the current family.

Currently, fonts for the devices -Tps, -Tpdf, -Tdvi, -Tlj4, -Tlbp, and the X11 fonts are set up to this mechanism.  By default, gtroff uses the Times family with the four styles R, I, B, and BI.

This way, it is possible to use the basic four fonts and to select a different font family on the command line (see Groff Options).

 -- Request: .fam, [family]
 -- Register: \n[.fam]
 -- Escape: \\F, , f,
 -- Escape: \\F, (, fm,
 -- Escape: \\F, [, family, ]
 -- Register: \n[.fn]
     Switch font family to FAMILY (one-character name F, two-character name FM).  If no argument is given, switch back to the previous font family.  Use \F[] to do this with the escape. Note that \FP doesn't work; it selects font family P instead.

     The value at start-up is T.  The current font family is available in the read-only number register .fam (this is a string-valued register); it is associated with the current environment.

          spam,
          .fam H    \" helvetica family
          spam,     \" used font is family H + style R = HR
          .ft B     \" family H + style B = font HB
          spam,
          .fam T    \" times family
          spam,     \" used font is family T + style B = TB
          .ft AR    \" font AR (not a style)
          baked beans,
          .ft R     \" family T + style R = font TR
          and spam.

     Note that \F doesn't produce an input token in gtroff.  As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font family on the fly:

          .mc \F[P]x\F[]

     The .fn register contains the current real font name of the current font.  This is a string-valued register.  If the current font is a style, the value of \n[.fn] is the proper concatenation of family and style name.

 -- Request: .sty, n style
     Associate STYLE with font position N.  A font position can be associated either with a font or with a style.  The current font is the index of a font position and so is also either a font or a style. If it is a style, the font that is actually used is the font which name is the concatenation of the name of the current family and the name of the current style.  For example, if the current font is 1 and font position 1 is associated with style R and the current font family is T, then font TR is used.  If the current font is not a style, then the current family is ignored.  If the requests cs, bd, tkf, uf, or fspecial are applied to a style, they are instead applied to the member of the current family corresponding to that style.

     N must be a non-negative integer value.

     The default family can be set with the -f option (see Groff Options).  The styles command in the DESC file controls which font positions (if any) are initially associated with styles rather than fonts.  For example, the default setting for POSTSCRIPT fonts

          styles R I B BI

     is equivalent to

          .sty 1 R
          .sty 2 I
          .sty 3 B
          .sty 4 BI

     fam and \F always check whether the current font position is valid; this can give surprising results if the current font position is associated with a style.

     In the following example, we want to access the POSTSCRIPT font FooBar from the font family Foo:

          .sty \n[.fp] Bar
          .fam Foo
              => warning: can't find font `FooR'

     The default font position at start-up is 1; for the POSTSCRIPT device, this is associated with style R, so gtroff tries to open FooR.

     A solution to this problem is to use a dummy font like the following:

          .fp 0 dummy TR    \" set up dummy font at position 0
          .sty \n[.fp] Bar  \" register style `Bar'
          .ft 0             \" switch to font at position 0
          .fam Foo          \" activate family `Foo'
          .ft Bar           \" switch to font `FooBar'

     See Font Positions.

Font Positions
--------------

For the sake of old phototypesetters and compatibility with old versions of troff, gtroff has the concept of font positions, on which various fonts are mounted.

 -- Request: .fp, pos font [external-name]
 -- Register: \n[.f]
 -- Register: \n[.fp]
     Mount font FONT at position POS (which must be a non-negative integer).  This numeric position can then be referred to with font changing commands.  When gtroff starts it is using font position 1 (which must exist; position 0 is unused usually at start-up).

     The current font in use, as a font position, is available in the read-only number register .f.  This can be useful to remember the current font for later recall.  It is associated with the current environment (see Environments).

          .nr save-font \n[.f]
          .ft B
          ... text text text ...
          .ft \n[save-font]

     The number of the next free font position is available in the read-only number register .fp.  This is useful when mounting a new font, like so:

          .fp \n[.fp] NEATOFONT

     Fonts not listed in the DESC file are automatically mounted on the next available font position when they are referenced.  If a font is to be mounted explicitly with the fp request on an unused font position, it should be mounted on the first unused font position, which can be found in the .fp register.  Although gtroff does not enforce this strictly, it is not allowed to mount a font at a position whose number is much greater (approx. 1000 positions) than that of any currently used position.

     The fp request has an optional third argument.  This argument gives the external name of the font, which is used for finding the font description file.  The second argument gives the internal name of the font, which is used to refer to the font in gtroff after it has been mounted.  If there is no third argument then the internal name is used as the external name.  This feature makes it possible to use fonts with long names in compatibility mode.

Both the ft request and the \f escape have alternative syntax forms to access font positions.

 -- Request: .ft, nnn
 -- Escape: \\f, , n,
 -- Escape: \\f, (, nn,
 -- Escape: \\f, [, nnn, ]
     Change the current font position to NNN (one-digit position N, two-digit position NN), which must be a non-negative integer.

     If NNN is associated with a style (as set with the sty request or with the styles command in the DESC file), use it within the current font family (as set with the fam request, the \F escape, or the family command in the DESC file).

          this is font 1
          .ft 2
          this is font 2
          .ft                   \" switch back to font 1
          .ft 3
          this is font 3
          .ft
          this is font 1 again

     See Changing Fonts, for the standard syntax form.

Using Symbols
-------------

A glyph is a graphical representation of a character.  While a character is an abstract entity containing semantic information, a glyph is something that can be actually seen on screen or paper.  It is possible that a character has multiple glyph representation forms (for example, the character `A' can be either written in a roman or an italic font, yielding two different glyphs); sometimes more than one character maps to a single glyph (this is a ligature -- the most common is `fi').

A symbol is simply a named glyph.  Within gtroff, all glyph names of a particular font are defined in its font file.  If the user requests a glyph not available in this font, gtroff looks up an ordered list of special fonts.  By default, the POSTSCRIPT output device supports the two special fonts SS (slanted symbols) and S (symbols) (the former is looked up before the latter). Other output devices use different names for special fonts.  Fonts mounted with the fonts keyword in the DESC file are globally available.  To install additional special fonts locally (i.e. for a particular font), use the fspecial request.

Here are the exact rules how gtroff searches a given symbol:

  * If the symbol has been defined with the char request, use it. This hides a symbol with the same name in the current font.

  * Check the current font.

  * If the symbol has been defined with the fchar request, use it.

  * Check whether the current font has a font-specific list of special fonts; test all fonts in the order of appearance in the last fspecial call if appropriate.

  * If the symbol has been defined with the fschar request for the current font, use it.

  * Check all fonts in the order of appearance in the last special call.

  * If the symbol has been defined with the schar request, use it.

  * As a last resort, consult all fonts loaded up to now for special fonts and check them, starting with the lowest font number.  Note that this can sometimes lead to surprising results since the fonts line in the DESC file often contains empty positions, which are filled later on.  For example, consider the following:

          fonts 3 0 0 FOO

     This mounts font foo at font position 3.  We assume that FOO is a special font, containing glyph foo, and that no font has been loaded yet.  The line

          .fspecial BAR BAZ

     makes font BAZ special only if font BAR is active.  We further assume that BAZ is really a special font, i.e., the font description file contains the special keyword, and that it also contains glyph foo with a special shape fitting to font BAR.  After executing fspecial, font BAR is loaded at font position 1, and BAZ at position 2.

     We now switch to a new font XXX, trying to access glyph foo that is assumed to be missing.  There are neither font-specific special fonts for XXX nor any other fonts made special with the special request, so gtroff starts the search for special fonts in the list of already mounted fonts, with increasing font positions.  Consequently, it finds BAZ before FOO even for XXX, which is not the intended behaviour.

See Font Files, and Special Fonts, for more details.

The list of available symbols is device dependent; see the groff_char(7) man page for a complete list of all glyphs.  For example, say

     man -Tdvi groff_char > groff_char.dvi

for a list using the default DVI fonts (not all versions of the man program support the -T option).  If you want to use an additional macro package to change the used fonts, groff must be called directly:

     groff -Tdvi -mec -man groff_char.7 > groff_char.dvi

Glyph names not listed in groff_char(7) are derived algorithmically, using a simplified version of the Adobe Glyph List (AGL) algorithm, which is described in https://github.com/adobe-type-tools/agl-aglfn. The (frozen) set of glyph names that can't be derived algorithmically is called groff glyph list (GGL).

  * A glyph for Unicode character U+XXXX[X[X]], which is not a composite character is named uXXXX[X[X]].  X must be an uppercase hexadecimal digit.  Examples: u1234, u008E, u12DB8.  The largest Unicode value is 0x10FFFF.  There must be at least four X digits; if necessary, add leading zeroes (after the u).  No zero padding is allowed for character codes greater than 0xFFFF.  Surrogates (i.e., Unicode values greater than 0xFFFF represented with character codes from the surrogate area U+D800-U+DFFF) are not allowed too.

  * A glyph representing more than a single input character is named

          u COMPONENT1 _ COMPONENT2 _ COMPONENT3 ...

     Example: u0045_0302_0301.

     For simplicity, all Unicode characters that are composites must be decomposed maximally (this is normalization form D in the Unicode standard); for example, u00CA_0301 is not a valid glyph name since U+00CA (LATIN CAPITAL LETTER E WITH CIRCUMFLEX) can be further decomposed into U+0045 (LATIN CAPITAL LETTER E) and U+0302 (COMBINING CIRCUMFLEX ACCENT).  u0045_0302_0301 is thus the glyph name for U+1EBE, LATIN CAPITAL LETTER E WITH CIRCUMFLEX AND ACUTE.

  * groff maintains a table to decompose all algorithmically derived glyph names that are composites itself.  For example, u0100 (LATIN LETTER A WITH MACRON) is automatically decomposed into u0041_0304.  Additionally, a glyph name of the GGL is preferred to an algorithmically derived glyph name; groff also automatically does the mapping.  Example: The glyph u0045_0302 is mapped to ^E.

  * glyph names of the GGL can't be used in composite glyph names; for example, ^E_u0301 is invalid.

 -- Escape: \\, (, nm,
 -- Escape: \\, [, name, ]
 -- Escape: \\, [, component1 component2 ..., ]
     Insert a symbol NAME (two-character name NM) or a composite glyph with component glyphs COMPONENT1, COMPONENT2, ... There is no special syntax for one-character names -- the natural form \N would collide with escapes. (Note that a one-character symbol is not the same as an input character, i.e., the character a is not the same as \[a].  By default, groff defines only a single one-character symbol, \[-]; it is usually accessed as \-.  On the other hand, gtroff has the special feature that \[charXXX] is the same as the input character with character code XXX.  For example, \[char97] is identical to the letter a if ASCII encoding is active.)

     If NAME is undefined, a warning of type char is generated, and the escape is ignored.  See Debugging, for information about warnings.

     groff resolves \[...] with more than a single component as follows:

       * Any component that is found in the GGL is converted to the uXXXX form.

       * Any component uXXXX that is found in the list of decomposable glyphs is decomposed.

       * The resulting elements are then concatenated with _ in between, dropping the leading u in all elements but the first.

     No check for the existence of any component (similar to tr request) is done.

     Examples:

     \[A ho]
          A maps to u0041, ho maps to u02DB, thus the final glyph name would be u0041_02DB.  Note this is not the expected result: The ogonek glyph ho is a spacing ogonek, but for a proper composite a non-spacing ogonek (U+0328) is necessary.  Looking into the file composite.tmac one can find .composite ho u0328, which changes the mapping of ho while a composite glyph name is constructed, causing the final glyph name to be u0041_0328.

     \[^E u0301]
     \[^E aa]
     \[E a^ aa]
     \[E ^ ']
          ^E maps to u0045_0302, thus the final glyph name is u0045_0302_0301 in all forms (assuming proper calls of the composite request).

     It is not possible to define glyphs with names like A ho within a groff font file.  This is not really a limitation; instead, you have to define u0041_0328.

 -- Escape: \\C, ', xxx, '
     Typeset the glyph named XXX. (\C is actually a misnomer since it accesses an output glyph.)  Normally it is more convenient to use \[XXX], but \C has the advantage that it is compatible with newer versions of AT&T troff and is available in compatibility mode.

 -- Request: .composite, from to
     Map glyph name FROM to glyph name TO if it is used in \[...] with more than one component.  See above for examples.

     This mapping is based on glyph names only; no check for the existence of either glyph is done.

     A set of default mappings for many accents can be found in the file composite.tmac, which is loaded at start-up.

 -- Escape: \\N, ', n, '
     Typeset the glyph with code N in the current font (n is not the input character code).  The number N can be any non-negative decimal integer.  Most devices only have glyphs with codes between 0 and 255; the Unicode output device uses codes in the range 0--65535.  If the current font does not contain a glyph with that code, special fonts are not searched.  The \N escape sequence can be conveniently used in conjunction with the char request:

          .char \[phone] \f[ZD]\N'37'

     The code of each glyph is given in the fourth column in the font description file after the charset command.  It is possible to include unnamed glyphs in the font description file by using a name of ---; the \N escape sequence is the only way to use these.

     No kerning is applied to glyphs accessed with \N.

Some escape sequences directly map onto special glyphs.

 -- Escape: \\', , ,
     This is a backslash followed by the apostrophe character, ASCII character 0x27 (EBCDIC character 0x7D).  The same as \[aa], the acute accent.

 -- Escape: \\`, , ,
     This is a backslash followed by ASCII character 0x60 (EBCDIC character 0x79 usually).  The same as \[ga], the grave accent.

 -- Escape: \\-, , ,
     This is the same as \[-], the minus sign in the current font.

 -- Escape: \\_, , ,
     This is the same as \[ul], the underline character.

 -- Request: .cflags, n c1 c2 ...
     Input characters and symbols have certain properties associated with it. (Note that the output glyphs themselves don't have such properties.  For gtroff, a glyph is a numbered box with a given width, depth, and height, nothing else.  All manipulations with the cflags request work on the input level.)  These properties can be modified with the cflags request.  The first argument is the sum of the desired flags and the remaining arguments are the characters or symbols to have those properties.  It is possible to omit the spaces between the characters or symbols.  Instead of single characters or symbols you can also use character classes (see Character Classes for more details).

     1
          The character ends sentences (initially characters .?! have this property).

     2
          Lines can be broken before the character (initially no characters have this property).  This only works if both the characters before and after have non-zero hyphenation codes (as set with the hcode request). Use value 64 to override this behaviour.

     4
          Lines can be broken after the character (initially the character - and the symbols \[hy] and \[em] have this property).  This only works if both the characters before and after have non-zero hyphenation codes (as set with the hcode request).  Use value 64 to override this behaviour.

     8
          The character overlaps horizontally if used as a horizontal line building element.  Initially the symbols \[ul], \[rn], \[ru], \[radicalex], and \[sqrtex] have this property.

     16
          The character overlaps vertically if used as vertical line building element.  Initially symbol \[br] has this property.

     32
          An end-of-sentence character followed by any number of characters with this property is treated as the end of a sentence if followed by a newline or two spaces; in other words the character is transparent for the purposes of end-of-sentence recognition -- this is the same as having a zero space factor in TeX (initially characters "')]* and the symbols \[dg], \[rq], and \[cq] have this property).

     64
          Ignore hyphenation code values of the surrounding characters.  Use this in combination with values 2 and 4 (initially no characters have this property).  For example, if you need an automatic break point after the en-dash in number ranges like `3000--5000', insert

               .cflags 68 \(en

          into your document.  Note, however, that this can lead to bad layout if done without thinking; in most situations, a better solution instead of changing the cflags value is to insert \: right after the hyphen at the places that really need a break point.

     128
          Prohibit a line break before the character, but allow a line break after the character.  This works only in combination with flags 256 and 512 (see below) and has no effect otherwise.

     256
          Prohibit a line break after the character, but allow a line break before the character.  This works only in combination with flags 128 and 512 (see below) and has no effect otherwise.

     512
          Allow line break before or after the character.  This works only in combination with flags 128 and 256 and has no effect otherwise.

          Contrary to flag values 2 and 4, the flags 128, 256, and 512 work pairwise.  If, for example, the left character has value 512, and the right character 128, no line break gets inserted.  If we use value 6 instead for the left character, a line break after the character can't be suppressed since the right neighbour character doesn't get examined.

 -- Request: .char, g [string]
 -- Request: .fchar, g [string]
 -- Request: .fschar, f g [string]
 -- Request: .schar, g [string]
     Define a new glyph G to be STRING (which can be empty). (char is a misnomer since an output glyph is defined.)  Every time glyph G needs to be printed, STRING is processed in a temporary environment and the result is wrapped up into a single object.  Compatibility mode is turned off and the escape character is set to \ while STRING is being processed.  Any emboldening, constant spacing or track kerning is applied to this object rather than to individual characters in STRING.

     A glyph defined by these requests can be used just like a normal glyph provided by the output device.  In particular, other characters can be translated to it with the tr or trin requests; it can be made the leader character by the lc request; repeated patterns can be drawn with the glyph using the \l and \L escape sequences; words containing the glyph can be hyphenated correctly if the hcode request is used to give the glyph's symbol a hyphenation code.

     There is a special anti-recursion feature: Use of g within the glyph's definition is handled like normal characters and symbols not defined with char.

     Note that the tr and trin requests take precedence if char accesses the same symbol.

          .tr XY
          X
              => Y
          .char X Z
          X
              => Y
          .tr XX
          X
              => Z

     The fchar request defines a fallback glyph: gtroff only checks for glyphs defined with fchar if it cannot find the glyph in the current font.  gtroff carries out this test before checking special fonts.

     fschar defines a fallback glyph for font F: gtroff checks for glyphs defined with fschar after the list of fonts declared as font-specific special fonts with the fspecial request, but before the list of fonts declared as global special fonts with the special request.

     Finally, the schar request defines a global fallback glyph: gtroff checks for glyphs defined with schar after the list of fonts declared as global special fonts with the special request, but before the already mounted special fonts.

     See Using Symbols, for a detailed description of the glyph searching mechanism in gtroff.

 -- Request: .rchar, c1 c2 ...
 -- Request: .rfschar, f c1 c2 ...
     Remove the definitions of glyphs C1, C2, ... This undoes the effect of a char, fchar, or schar request.

     It is possible to omit the whitespace between arguments.

     The request rfschar removes glyph definitions defined with fschar for glyph f.

See Special Characters.

Character Classes
-----------------

Classes are particularly useful for East Asian languages such as Chinese, Japanese, and Korean, where the number of needed characters is much larger than in European languages, and where large sets of characters share the same properties.

 -- Request: .class, n c1 c2 ...
     In groff, a character class (or simply ``class'') is a set of characters, grouped by some user aspect.  The class request defines such classes so that other requests can refer to all characters belonging to this set with a single class name.  Currently, only the cflags request can handle character classes.

     A class request takes a class name followed by a list of entities.  In its simplest form, the entities are characters or symbols:

          .class [prepunct] , : ; > }

     Since class and glyph names share the same namespace, it is recommended to start and end the class name with [ and ], respectively, to avoid collisions with normal groff symbols (and symbols defined by the user).  In particular, the presence of ] in the symbol name intentionally prevents the usage of \[...], thus you must use the \C escape to access a class with such a name.

     You can also use a special character range notation, consisting of a start character or symbol, followed by -, and an end character or symbol.  Internally, gtroff converts these two symbol names to Unicode values (according to the groff glyph gist), which then give the start and end value of the range.  If that fails, the class definition is skipped.

     Finally, classes can be nested, too.

     Here is a more complex example:

          .class [prepunctx] \C'[prepunct]' \[u2013]-\[u2016]

     The class prepunctx now contains the contents of the class prepunct as defined above (the set , : ; > }), and characters in the range between U+2013 and U+2016.

     If you want to add - to a class, it must be the first character value in the argument list, otherwise it gets misinterpreted as a range.

     Note that it is not possible to use class names within range definitions.

     Typical use of the class request is to control line-breaking and hyphenation rules as defined by the cflags request.  For example, to inhibit line breaks before the characters belonging to the prepunctx class, you can write:

          .cflags 2 \C'[prepunctx]'

     See the cflags request in Using Symbols, for more details.

Special Fonts
-------------

Special fonts are those that gtroff searches when it cannot find the requested glyph in the current font.  The Symbol font is usually a special font.

gtroff provides the following two requests to add more special fonts.  See Using Symbols, for a detailed description of the glyph searching mechanism in gtroff.

Usually, only non-TTY devices have special fonts.

 -- Request: .special, [s1 s2 ...]
 -- Request: .fspecial, f [s1 s2 ...]
     Use the special request to define special fonts.  Initially, this list is empty.

     Use the fspecial request to designate special fonts only when font F is active.  Initially, this list is empty.

     Previous calls to special or fspecial are overwritten; without arguments, the particular list of special fonts is set to empty. Special fonts are searched in the order they appear as arguments.

     All fonts that appear in a call to special or fspecial are loaded.

     See Using Symbols, for the exact search order of glyphs.

Artificial Fonts
----------------

There are a number of requests and escapes for artificially creating fonts.  These are largely vestiges of the days when output devices did not have a wide variety of fonts, and when nroff and troff were separate programs.  Most of them are no longer necessary in GNU troff.  Nevertheless, they are supported.

 -- Escape: \\H, ', height, '
 -- Escape: \\H, ', +height, '
 -- Escape: \\H, ', -height, '
 -- Register: \n[.height]
     Change (increment, decrement) the height of the current font, but not the width.  If HEIGHT is zero, restore the original height. Default scaling indicator is z.

     The read-only number register .height contains the font height as set by \H.

     Currently, only the -Tps and -Tpdf devices support this feature.

     Note that \H doesn't produce an input token in gtroff.  As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font on the fly:

          .mc \H'+5z'x\H'0'

     In compatibility mode, gtroff behaves differently: If an increment or decrement is used, it is always taken relative to the current point size and not relative to the previously selected font height.  Thus,

          .cp 1
          \H'+5'test \H'+5'test

     prints the word test twice with the same font height (five points larger than the current font size).

 -- Escape: \\S, ', slant, '
 -- Register: \n[.slant]
     Slant the current font by SLANT degrees.  Positive values slant to the right.  Only integer values are possible.

     The read-only number register .slant contains the font slant as set by \S.

     Currently, only the -Tps and -Tpdf devices support this feature.

     Note that \S doesn't produce an input token in gtroff.  As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font on the fly:

          .mc \S'20'x\S'0'

     This request is incorrectly documented in the original Unix troff manual; the slant is always set to an absolute value.

 -- Request: .ul, [lines]
     The ul request normally underlines subsequent lines if a TTY output device is used.  Otherwise, the lines are printed in italics (only the term `underlined' is used in the following).  The single argument is the number of input lines to be underlined; with no argument, the next line is underlined.  If LINES is zero or negative, stop the effects of ul (if it was active).  Requests and empty lines do not count for computing the number of underlined input lines, even if they produce some output like tl.  Lines inserted by macros (e.g. invoked by a trap) do count.

     At the beginning of ul, the current font is stored and the underline font is activated.  Within the span of a ul request, it is possible to change fonts, but after the last line affected by ul the saved font is restored.

     This number of lines still to be underlined is associated with the current environment (see Environments).  The underline font can be changed with the uf request.

     The ul request does not underline spaces.

 -- Request: .cu, [lines]
     The cu request is similar to ul but underlines spaces as well (if a TTY output device is used).

 -- Request: .uf, font
     Set the underline font (globally) used by ul and cu.  By default, this is the font at position 2.  FONT can be either a non-negative font position or the name of a font.

 -- Request: .bd, font [offset]
 -- Request: .bd, font1 font2 [offset]
 -- Register: \n[.b]
     Artificially create a bold font by printing each glyph twice, slightly offset.

     Two syntax forms are available.

       * Imitate a bold font unconditionally.  The first argument specifies the font to embolden, and the second is the number of basic units, minus one, by which the two glyphs are offset.  If the second argument is missing, emboldening is turned off.

          FONT can be either a non-negative font position or the name of a font.

          OFFSET is available in the .b read-only register if a special font is active; in the bd request, its default unit is u.

       * Imitate a bold form conditionally.  Embolden FONT1 by OFFSET only if font FONT2 is the current font.  This command can be issued repeatedly to set up different emboldening values for different current fonts.  If the second argument is missing, emboldening is turned off for this particular current font.

          This affects special fonts only (either set up with the special command in font files or with the fspecial request).

 -- Request: .cs, font [width [em-size]]
     Switch to and from constant glyph space mode.  If activated, the width of every glyph is WIDTH/36 ems.  The em size is given absolutely by EM-SIZE; if this argument is missing, the em value is taken from the current font size (as set with the ps request) when the font is effectively in use.  Without second and third argument, constant glyph space mode is deactivated.

     Default scaling indicator for EM-SIZE is z; WIDTH is an integer.

Ligatures and Kerning
---------------------

Ligatures are groups of characters that are run together, i.e, producing a single glyph.  For example, the letters `f' and `i' can form a ligature `fi' as in the word `file'.  This produces a cleaner look (albeit subtle) to the printed output.  Usually, ligatures are not available in fonts for TTY output devices.

Most POSTSCRIPT fonts support the fi and fl ligatures.  The C/A/T typesetter that was the target of AT&T troff also supported `ff', `ffi', and `ffl' ligatures.  Advanced typesetters or `expert' fonts may include ligatures for `ft' and `ct', although GNU troff does not support these (yet).

Only the current font is checked for ligatures and kerns; neither special fonts nor entities defined with the char request (and its siblings) are taken into account.

 -- Request: .lg, [flag]
 -- Register: \n[.lg]
     Switch the ligature mechanism on or off; if the parameter is non-zero or missing, ligatures are enabled, otherwise disabled.  Default is on.  The current ligature mode can be found in the read-only number register .lg (set to 1 or 2 if ligatures are enabled, 0 otherwise).

     Setting the ligature mode to 2 enables the two-character ligatures (fi, fl, and ff) and disables the three-character ligatures (ffi and ffl).

Pairwise kerning is another subtle typesetting mechanism that modifies the distance between a glyph pair to improve readability.  In most cases (but not always) the distance is decreased. Typewriter-like fonts and fonts for terminals where all glyphs have the same width don't use kerning.

 -- Request: .kern, [flag]
 -- Register: \n[.kern]
     Switch kerning on or off.  If the parameter is non-zero or missing, enable pairwise kerning, otherwise disable it.  The read-only number register .kern is set to 1 if pairwise kerning is enabled, 0 otherwise.

     If the font description file contains pairwise kerning information, glyphs from that font are kerned.  Kerning between two glyphs can be inhibited by placing \& between them: V\&A.

     See Font File Format.

Track kerning expands or reduces the space between glyphs.  This can be handy, for example, if you need to squeeze a long word onto a single line or spread some text to fill a narrow column.  It must be used with great care since it is usually considered bad typography if the reader notices the effect.

 -- Request: .tkf, f s1 n1 s2 n2
     Enable track kerning for font F.  If the current font is F the width of every glyph is increased by an amount between N1 and N2 (N1, N2 can be negative); if the current point size is less than or equal to S1 the width is increased by N1; if it is greater than or equal to S2 the width is increased by N2; if the point size is greater than or equal to S1 and less than or equal to S2 the increase in width is a linear function of the point size.

     The default scaling indicator is z for S1 and S2, p for N1 and N2.

     Note that the track kerning amount is added even to the rightmost glyph in a line; for large values it is thus recommended to increase the line length by the same amount to compensate it.

Sometimes, when typesetting letters of different fonts, more or less space at such boundaries is needed.  There are two escapes to help with this.

 -- Escape: \\/, , ,
     Increase the width of the preceding glyph so that the spacing between that glyph and the following glyph is correct if the following glyph is a roman glyph.  For example, if an italic f is immediately followed by a roman right parenthesis, then in many fonts the top right portion of the f overlaps the top left of the right parenthesis.  Use this escape sequence whenever an italic glyph is immediately followed by a roman glyph without any intervening space. This small amount of space is also called italic correction.

 -- Escape: \\\,, , ,
     Modify the spacing of the following glyph so that the spacing between that glyph and the preceding glyph is correct if the preceding glyph is a roman glyph.  Use this escape sequence whenever a roman glyph is immediately followed by an italic glyph without any intervening space. In analogy to above, this space could be called left italic correction, but this term isn't used widely.

 -- Escape: \\&, , ,
     Insert a zero-width character, which is invisible.  Its intended use is to stop interaction of a character with its surroundings.

       * It prevents the insertion of extra space after an end-of-sentence character.

               Test.
               Test.
                   => Test.  Test.
               Test.\&
               Test.
                   => Test. Test.

       * It prevents interpretation of a control character at the beginning of an input line.

               .Test
                   => warning: `Test' not defined
               \&.Test
                   => .Test

       * It prevents kerning between two glyphs.

       * It is needed to map an arbitrary character to nothing in the tr request (see Character Translations).

 -- Escape: \\), , ,
     This escape is similar to \& except that it behaves like a character declared with the cflags request to be transparent for the purposes of an end-of-sentence character.

     Its main usage is in macro definitions to protect against arguments starting with a control character.

          .de xxx
          \)\\$1
          ..
          .de yyy
          \&\\$1
          ..
          This is a test.\c
          .xxx '
          This is a test.
              =>This is a test.'  This is a test.
          This is a test.\c
          .yyy '
          This is a test.
              =>This is a test.' This is a test.

Sizes
=====

gtroff uses two dimensions with each line of text, type size and vertical spacing.  The type size is approximately the height of the tallest glyph. (This is usually the parenthesis.  Note that in most cases the real dimensions of the glyphs in a font are not related to its type size!  For example, the standard POSTSCRIPT font families `Times Roman', `Helvetica', and `Courier' can't be used together at 10pt; to get acceptable output, the size of `Helvetica' has to be reduced by one point, and the size of `Courier' must be increased by one point.)  Vertical spacing is the amount of space gtroff allows for a line of text; normally, this is about 20% larger than the current type size.  Ratios smaller than this can result in hard-to-read text; larger than this, it spreads the text out more vertically (useful for term papers).  By default, gtroff uses 10 point type on 12 point spacing.

The difference between type size and vertical spacing is known, by typesetters, as leading (this is pronounced `ledding').

Changing Type Sizes
-------------------

 -- Request: .ps, [size]
 -- Request: .ps, +size
 -- Request: .ps, -size
 -- Escape: \\s, , size,
 -- Register: \n[.s]
     Use the ps request or the \s escape to change (increase, decrease) the type size (in points).  Specify SIZE as either an absolute point size, or as a relative change from the current size.  The size 0 (for both .ps and \s), or no argument (for .ps only), goes back to the previous size.

     Default scaling indicator of size is z.  If size is negative, it is set to 1u.

     The read-only number register .s returns the point size in points as a decimal fraction.  This is a string.  To get the point size in scaled points, use the .ps register instead.

     .s is associated with the current environment (see Environments).

          snap, snap,
          .ps +2
          grin, grin,
          .ps +2
          wink, wink, \s+2nudge, nudge,\s+8 say no more!
          .ps 10

     The \s escape may be called in a variety of ways.  Much like other escapes there must be a way to determine where the argument ends and the text begins.  Any of the following forms are valid:

     \sN
          Set the point size to N points.  N must be either 0 or in the range 4 to 39.

     \s+N
     \s-N
          Increase or decrease the point size by N points. N must be exactly one digit.

     \s(NN
          Set the point size to NN points.  NN must be exactly two digits.

     \s+(NN
     \s-(NN
     \s(+NN
     \s(-NN
          Increase or decrease the point size by NN points.  NN must be exactly two digits.

     Note that \s doesn't produce an input token in gtroff.  As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font on the fly:

          .mc \s[20]x\s[0]

     See Fractional Type Sizes, for yet another syntactical form of using the \s escape.

 -- Request: .sizes, s1 s2 ... sn [0]
     Some devices may only have certain permissible sizes, in which case gtroff rounds to the nearest permissible size.  The DESC file specifies which sizes are permissible for the device.

     Use the sizes request to change the permissible sizes for the current output device.  Arguments are in scaled points; the sizescale line in the DESC file for the output device provides the scaling factor.  For example, if the scaling factor is 1000, then the value 12000 is 12 points.

     Each argument can be a single point size (such as 12000), or a range of sizes (such as 4000-72000).  You can optionally end the list with a zero.

 -- Request: .vs, [space]
 -- Request: .vs, +space
 -- Request: .vs, -space
 -- Register: \n[.v]
     Change (increase, decrease) the vertical spacing by SPACE.  The default scaling indicator is p.

     If vs is called without an argument, the vertical spacing is reset to the previous value before the last call to vs.

     gtroff creates a warning of type range if SPACE is negative; the vertical spacing is then set to smallest positive value, the vertical resolution (as given in the .V register).

     Note that .vs 0 isn't saved in a diversion since it doesn't result in a vertical motion.  You explicitly have to repeat this command before inserting the diversion.

     The read-only number register .v contains the current vertical spacing; it is associated with the current environment (see Environments).

The effective vertical line spacing consists of four components. Breaking a line causes the following actions (in the given order).

  * Move the current point vertically by the extra pre-vertical line space.  This is the minimum value of all \x escapes with a negative argument in the current output line.

  * Move the current point vertically by the vertical line spacing as set with the vs request.

  * Output the current line.

  * Move the current point vertically by the extra post-vertical line space.  This is the maximum value of all \x escapes with a positive argument in the line that has just been output.

  * Move the current point vertically by the post-vertical line spacing as set with the pvs request.

It is usually better to use vs or pvs instead of ls to produce double-spaced documents: vs and pvs have a finer granularity for the inserted vertical space compared to ls; furthermore, certain preprocessors assume single-spacing.

See Manipulating Spacing, for more details on the \x escape and the ls request.

 -- Request: .pvs, [space]
 -- Request: .pvs, +space
 -- Request: .pvs, -space
 -- Register: \n[.pvs]
     Change (increase, decrease) the post-vertical spacing by SPACE. The default scaling indicator is p.

     If pvs is called without an argument, the post-vertical spacing is reset to the previous value before the last call to pvs.

     gtroff creates a warning of type range if SPACE is zero or negative; the vertical spacing is then set to zero.

     The read-only number register .pvs contains the current post-vertical spacing; it is associated with the current environment (see Environments).

Fractional Type Sizes
---------------------

A scaled point is equal to 1/SIZESCALE points, where SIZESCALE is specified in the DESC file (1 by default).  There is a new scale indicator z, which has the effect of multiplying by SIZESCALE.  Requests and escape sequences in gtroff interpret arguments that represent a point size as being in units of scaled points, but they evaluate each such argument using a default scale indicator of z.  Arguments treated in this way are the argument to the ps request, the third argument to the cs request, the second and fourth arguments to the tkf request, the argument to the \H escape sequence, and those variants of the \s escape sequence that take a numeric expression as their argument (see below).

For example, suppose SIZESCALE is 1000; then a scaled point is equivalent to a millipoint; the request .ps 10.25 is equivalent to .ps 10.25z and thus sets the point size to 10250 scaled points, which is equal to 10.25 points.

gtroff disallows the use of the z scale indicator in instances where it would make no sense, such as a numeric expression whose default scale indicator was neither u nor z. Similarly it would make no sense to use a scaling indicator other than z or u in a numeric expression whose default scale indicator was z, and so gtroff disallows this as well.

There is also new scale indicator s, which multiplies by the number of units in a scaled point.  So, for example, \n[.ps]s is equal to 1m.  Be sure not to confuse the s and z scale indicators.

 -- Register: \n[.ps]
     A read-only number register returning the point size in scaled points.

     .ps is associated with the current environment (see Environments).

 -- Register: \n[.psr]
 -- Register: \n[.sr]
     The last-requested point size in scaled points is contained in the .psr read-only number register.  The last requested point size in points as a decimal fraction can be found in .sr.  This is a string-valued read-only number register.

     Note that the requested point sizes are device-independent, whereas the values returned by the .ps and .s registers are not.  For example, if a point size of 11pt is requested, and a sizes request (or a sizescale line in a DESC file) specifies 10.95pt instead, this value is actually used.

     Both registers are associated with the current environment (see Environments).

The \s escape has the following syntax for working with fractional type sizes:

\s[N]
\s'N'
     Set the point size to N scaled points; N is a numeric expression with a default scale indicator of z.

\s[+N]
\s[-N]
\s+[N]
\s-[N]
\s'+N'
\s'-N'
\s+'N'
\s-'N'
     Increase or decrease the point size by N scaled points; N is a numeric expression (which may start with a minus sign) with a default scale indicator of z.

See Font Files.

Strings
=======

gtroff has string variables, which are entirely for user convenience (i.e. there are no built-in strings except .T, but even this is a read-write string variable).

Although the following requests can be used to create strings, simply using an undefined string will cause it to be defined as empty. See Identifiers.

 -- Request: .ds, name [string]
 -- Request: .ds1, name [string]
 -- Escape: \\*, , n,
 -- Escape: \\*, (, nm,
 -- Escape: \\*, [, name arg1 arg2 ..., ]
     Define and access a string variable NAME (one-character name N, two-character name NM).  If NAME already exists, ds overwrites the previous definition.  Only the syntax form using brackets can take arguments that are handled identically to macro arguments; the single exception is that a closing bracket as an argument must be enclosed in double quotes.  See Request and Macro Arguments, and Parameters.

     Example:

          .ds foo a \\$1 test
          .
          This is \*[foo nice].
              => This is a nice test.

     The \* escape interpolates (expands in-place) a previously defined string variable.  To be more precise, the stored string is pushed onto the input stack, which is then parsed by gtroff.  Similar to number registers, it is possible to nest strings, i.e., string variables can be called within string variables.

     If the string named by the \* escape does not exist, it is defined as empty, and a warning of type mac is emitted (see Debugging, for more details).

     Caution: Unlike other requests, the second argument to the ds request takes up the entire line including trailing spaces. This means that comments on a line with such a request can introduce unwanted space into a string.

          .ds TeX T\h'-.2m'\v'.2m'E\v'-.2m'\h'-.1m'X \" Knuth's TeX

     Instead the comment should be put on another line or have the comment escape adjacent with the end of the string.

          .ds TeX T\h'-.2m'\v'.2m'E\v'-.2m'\h'-.1m'X\" Knuth's TeX

     To produce leading space the string can be started with a double quote. No trailing quote is needed; in fact, any trailing quote is included in your string.

          .ds sign "           Yours in a white wine sauce,

     Strings are not limited to a single line of text.  A string can span several lines by escaping the newlines with a backslash.  The resulting string is stored without the newlines.

          .ds foo lots and lots \
          of text are on these \
          next several lines

     It is not possible to have real newlines in a string.  To put a single double quote character into a string, use two consecutive double quote characters.

     The ds1 request turns off compatibility mode while interpreting a string.  To be more precise, a compatibility save input token is inserted at the beginning of the string, and a compatibility restore input token at the end.

          .nr xxx 12345
          .ds aa The value of xxx is \\n[xxx].
          .ds1 bb The value of xxx is \\n[xxx].
          .
          .cp 1
          .
          \*(aa
              => warning: number register `[' not defined
              => The value of xxx is 0xxx].
          \*(bb
              => The value of xxx is 12345.

     Strings, macros, and diversions (and boxes) share the same name space. Internally, even the same mechanism is used to store them.  This has some interesting consequences.  For example, it is possible to call a macro with string syntax and vice versa.

          .de xxx
          a funny test.
          ..
          This is \*[xxx]
              => This is a funny test.

          .ds yyy a funny test
          This is
          .yyy
              => This is a funny test.

     In particular, interpolating a string does not hide existing macro arguments.  Thus in a macro, a more efficient way of doing

          .xx \\$@

     is

          \\*[xx]\\

     Note that the latter calling syntax doesn't change the value of \$0, which is then inherited from the calling macro.

     Diversions and boxes can be also called with string syntax.

     Another consequence is that you can copy one-line diversions or boxes to a string.

          .di xxx
          a \fItest\fR
          .br
          .di
          .ds yyy This is \*[xxx]\c
          \*[yyy].
              => This is a test.

     As the previous example shows, it is possible to store formatted output in strings.  The \c escape prevents the insertion of an additional blank line in the output.

     Copying diversions longer than a single output line produces unexpected results.

          .di xxx
          a funny
          .br
          test
          .br
          .di
          .ds yyy This is \*[xxx]\c
          \*[yyy].
              => test This is a funny.

     Usually, it is not predictable whether a diversion contains one or more output lines, so this mechanism should be avoided.  With Unix troff, this was the only solution to strip off a final newline from a diversion.  Another disadvantage is that the spaces in the copied string are already formatted, making them unstretchable.  This can cause ugly results.

     A clean solution to this problem is available in GNU troff, using the requests chop to remove the final newline of a diversion, and unformat to make the horizontal spaces stretchable again.

          .box xxx
          a funny
          .br
          test
          .br
          .box
          .chop xxx
          .unformat xxx
          This is \*[xxx].
              => This is a funny test.

     See Gtroff Internals, for more information.

 -- Request: .as, name [string]
 -- Request: .as1, name [string]
     The as request is similar to ds but appends STRING to the string stored as NAME instead of redefining it.  If NAME doesn't exist yet, it is created.

          .as sign " with shallots, onions and garlic,

     The as1 request is similar to as, but compatibility mode is switched off while the appended string is interpreted.  To be more precise, a compatibility save input token is inserted at the beginning of the appended string, and a compatibility restore input token at the end.

Rudimentary string manipulation routines are given with the next two requests.

 -- Request: .substring, str n1 [n2]
     Replace the string named STR with the substring defined by the indices N1 and N2.  The first character in the string has index 0.  If N2 is omitted, it is implicitly set to the largest valid value (the string length minus one).  If the index value N1 or N2 is negative, it is counted from the end of the string, going backwards: The last character has index -1, the character before the last character has index -2, etc.

          .ds xxx abcdefgh
          .substring xxx 1 -4
          \*[xxx]
              => bcde
          .substring xxx 2
          \*[xxx]
              => de

 -- Request: .length, reg str
     Compute the number of characters of STR and return it in the number register REG.  If REG doesn't exist, it is created. str is read in copy mode.

          .ds xxx abcd\h'3i'efgh
          .length yyy \*[xxx]
          \n[yyy]
              => 14

 -- Request: .rn, xx yy
     Rename the request, macro, diversion, or string XX to YY.

 -- Request: .rm, xx
     Remove the request, macro, diversion, or string XX.  gtroff treats subsequent invocations as if the object had never been defined.

 -- Request: .als, new old
     Create an alias named NEW for the request, string, macro, or diversion object named OLD.  The new name and the old name are exactly equivalent (it is similar to a hard rather than a soft link).  If OLD is undefined, gtroff generates a warning of type mac and ignores the request.

     To understand how the als request works it is probably best to think of two different pools: one pool for objects (macros, strings, etc.), and another one for names.  As soon as an object is defined, gtroff adds it to the object pool, adds its name to the name pool, and creates a link between them.  When als creates an alias, it adds a new name to the name pool that gets linked to the same object as the old name.

     Now consider this example.

          .de foo
          ..
          .
          .als bar foo
          .
          .de bar
          .  foo
          ..
          .
          .bar
              => input stack limit exceeded

     The definition of macro bar replaces the old object this name is linked to.  However, the alias to foo is still active!  In other words, foo is still linked to the same object as bar, and the result of calling bar is an infinite, recursive loop that finally leads to an error.

     To undo an alias, simply call rm on the aliased name.  The object itself is not destroyed until there are no more aliases.

 -- Request: .chop, xx
     Remove (chop) the last character from the macro, string, or diversion named XX.  This is useful for removing the newline from the end of diversions that are to be interpolated as strings.  This command can be used repeatedly; see Gtroff Internals, for details on nodes inserted additionally by gtroff.

See Identifiers, and Comments.

Conditionals and Loops
======================

Operators in Conditionals
-------------------------

In if, ie, and while requests, in addition to ordinary Expressions, there are several more operators available:

e
o
     True if the current page is even or odd numbered (respectively).

n
     True if the document is being processed in nroff mode (i.e., the .nroff command has been issued).  See Troff and Nroff Mode.

t
     True if the document is being processed in troff mode (i.e., the .troff command has been issued).  See Troff and Nroff Mode.

v
     Always false.  This condition is for compatibility with other troff versions only (identifying a -Tversatec device).

'XXX'YYY'
     True if the output produced by XXX is equal to the output produced by YYY.  Other characters can be used in place of the single quotes; the same set of delimiters as for the \D escape is used (see Escapes).  gtroff formats XXX and YYY in separate environments; after the comparison the resulting data is discarded.

          .ie "|"\fR|\fP" \
          true
          .el \
          false
              => true

     The resulting motions, glyph sizes, and fonts have to match, (The created output nodes must be identical. See Gtroff Internals.) and not the individual motion, size, and font requests.  In the previous example, | and \fR|\fP both result in a roman | glyph with the same point size and at the same location on the page, so the strings are equal.  If .ft I had been added before the .ie, the result would be ``false'' because (the first) | produces an italic | rather than a roman one.

     To compare strings without processing, surround the data with \?.

          .ie "\?|\?"\?\fR|\fP\?" \
          true
          .el \
          false
              => false

     Since data protected with \? is read in copy-in mode it is even possible to use incomplete input without causing an error.

          .ds a \[
          .ds b \[
          .ie '\?\*a\?'\?\*b\?' \
          true
          .el \
          false
              => true

r XXX
     True if there is a number register named XXX.

d XXX
     True if there is a string, macro, diversion, or request named XXX.

m XXX
     True if there is a color named XXX.

c G
     True if there is a glyph G available (The name of this conditional operator is a misnomer since it tests names of output glyphs.); G is either an ASCII character or a special character (\N'XXX', \(GG or \[GGG]); the condition is also true if G has been defined by the char request.

F FONT
     True if a font named FONT exists.  FONT is handled as if it was opened with the ft request (that is, font translation and styles are applied), without actually mounting it.

     This test doesn't load the complete font but only its header to verify its validity.

S STYLE
     True if style STYLE has been registered.  Font translation is applied.

Note that these operators can't be combined with other operators like : or &; only a leading ! (without whitespace between the exclamation mark and the operator) can be used to negate the result.

     .nr xxx 1
     .ie !r xxx \
     true
     .el \
     false
         => false

A whitespace after ! always evaluates to zero (this bizarre behaviour is due to compatibility with Unix troff).

     .nr xxx 1
     .ie ! r xxx \
     true
     .el \
     false
         => r xxx true

It is possible to omit the whitespace before the argument to the r, d, and c operators.

See Expressions.

if-else
-------

gtroff has if-then-else constructs like other languages, although the formatting can be painful.

 -- Request: .if, expr anything

     Evaluate the expression EXPR, and executes ANYTHING (the remainder of the line) if EXPR evaluates to a value greater than zero (true).  ANYTHING is interpreted as though it was on a line by itself (except that leading spaces are swallowed). See Operators in Conditionals, for more info.

          .nr xxx 1
          .nr yyy 2
          .if ((\n[xxx] == 1) & (\n[yyy] == 2)) true
              => true

 -- Request: .nop, anything
     Executes ANYTHING.  This is similar to .if 1.

 -- Request: .ie, expr anything
 -- Request: .el, anything
     Use the ie and el requests to write an if-then-else.  The first request is the `if' part and the latter is the `else' part.

          .ie n .ls 2 \" double-spacing in nroff
          .el   .ls 1 \" single-spacing in troff

 -- Escape: \{
 -- Escape: \}
     In many cases, an if (or if-else) construct needs to execute more than one request.  This can be done using the escapes \{ (which must start the first line) and \} (which must end the last line).

          .ie t \{\
          .    ds lq ``
          .    ds rq ''
          .\}
          .el \{\
          .    ds lq ""
          .    ds rq ""
          .\}

See Expressions.

while
-----

gtroff provides a looping construct using the while request, which is used much like the if (and related) requests.

 -- Request: .while, expr anything
     Evaluate the expression EXPR, and repeatedly execute ANYTHING (the remainder of the line) until EXPR evaluates to 0.

          .nr a 0 1
          .while (\na < 9) \{\
          \n+a,
          .\}
          \n+a
              => 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

     Some remarks.

       * The body of a while request is treated like the body of a de request: gtroff temporarily stores it in a macro that is deleted after the loop has been exited.  It can considerably slow down a macro if the body of the while request (within the macro) is large.  Each time the macro is executed, the while body is parsed and stored again as a temporary macro.

               .de xxx
               .  nr num 10
               .  while (\\n[num] > 0) \{\
               .    \" many lines of code
               .    nr num -1
               .  \}
               ..

          The traditional and often better solution (Unix troff doesn't have the while request) is to use a recursive macro instead that is parsed only once during its definition.

               .de yyy
               .  if (\\n[num] > 0) \{\
               .    \" many lines of code
               .    nr num -1
               .    yyy
               .  \}
               ..
               .
               .de xxx
               .  nr num 10
               .  yyy
               ..

          Note that the number of available recursion levels is set to 1000 (this is a compile-time constant value of gtroff).

       * The closing brace of a while body must end a line.

               .if 1 \{\
               .  nr a 0 1
               .  while (\n[a] < 10) \{\
               .    nop \n+[a]
               .\}\}
                   => unbalanced \{ \}

 -- Request: .break,
     Break out of a while loop.  Be sure not to confuse this with the br request (causing a line break).

 -- Request: .continue,
     Finish the current iteration of a while loop, immediately restarting the next iteration.

See Expressions.

Writing Macros
==============

A macro is a collection of text and embedded commands that can be invoked multiple times.  Use macros to define common operations. See Strings, for a (limited) alternative syntax to call macros.

Although the following requests can be used to create macros, simply using an undefined macro will cause it to be defined as empty. See Identifiers.

 -- Request: .de, name [end]
 -- Request: .de1, name [end]
 -- Request: .dei, name [end]
 -- Request: .dei1, name [end]
     Define a new macro named NAME.  gtroff copies subsequent lines (starting with the next one) into an internal buffer until it encounters the line .. (two dots).  If the optional second argument to de is present it is used as the macro closure request instead of ...

     There can be whitespace after the first dot in the line containing the ending token (either . or macro END).  Don't insert a tab character immediately after the .., otherwise it isn't
     recognized as the end-of-macro symbol. (While it is possible to
     define and call a macro . with)

          .de .
          .  tm foo
          ..
          .
          ..    \" This calls macro `.'!

     you can't use this as the end-of-macro macro: during a macro definition, .. is never handled as a call to ., even if you say .de foo . explicitly.

     Here a small example macro called P that causes a break and inserts some vertical space.  It could be used to separate paragraphs.

          .de P
          .  br
          .  sp .8v
          ..

     The following example defines a macro within another.  Remember that expansion must be protected twice; once for reading the macro and once for executing.

          \# a dummy macro to avoid a warning
          .de end
          ..
          .
          .de foo
          .  de bar end
          .    nop \f[B]Hello \\\\$1!\f[]
          .  end
          ..
          .
          .foo
          .bar Joe
              => Hello Joe!

     Since \f has no expansion, it isn't necessary to protect its backslash.  Had we defined another macro within bar that takes a parameter, eight backslashes would be necessary before $1.

     The de1 request turns off compatibility mode while executing the macro.  On entry, the current compatibility mode is saved and restored at exit.

          .nr xxx 12345
          .
          .de aa
          The value of xxx is \\n[xxx].
          ..
          .de1 bb
          The value of xxx is \\n[xxx].
          ..
          .
          .cp 1
          .
          .aa
              => warning: number register `[' not defined
              => The value of xxx is 0xxx].
          .bb
              => The value of xxx is 12345.

     The dei request defines a macro indirectly.  That is, it expands strings whose names are NAME or END before performing the append.

     This:

          .ds xx aa
          .ds yy bb
          .dei xx yy

     is equivalent to:

          .de aa bb

     The dei1 request is similar to dei but with compatibility mode switched off during execution of the defined macro.

     If compatibility mode is on, de (and dei) behave similar to de1 (and dei1): A `compatibility save' token is inserted at the beginning, and a `compatibility restore' token at the end, with compatibility mode switched on during execution.  See Gtroff Internals, for more information on switching compatibility mode on and off in a single document.

     Using trace.tmac, you can trace calls to de and de1.

     Note that macro identifiers are shared with identifiers for strings and diversions.

     See the description of the als request, for possible pitfalls if redefining a macro that has been aliased.

 -- Request: .am, name [end]
 -- Request: .am1, name [end]
 -- Request: .ami, name [end]
 -- Request: .ami1, name [end]
     Works similarly to de except it appends onto the macro named NAME.  So, to make the previously defined P macro actually do indented instead of block paragraphs, add the necessary code to the existing macro like this:

          .am P
          .ti +5n
          ..

     The am1 request turns off compatibility mode while executing the appended macro piece.  To be more precise, a compatibility save input token is inserted at the beginning of the appended code, and a compatibility restore input token at the end.

     The ami request appends indirectly, meaning that gtroff expands strings whose names are NAME or END before performing the append.

     The ami1 request is similar to ami but compatibility mode is switched off during execution of the defined macro.

     Using trace.tmac, you can trace calls to am and am1.

See Strings, for the als and rn request to create an alias and rename a macro, respectively.

The de, am, di, da, ds, and as requests (together with their variants) only create a new object if the name of the macro, diversion or string is currently undefined or if it is defined to be a request; normally they modify the value of an existing object.

 -- Request: .return, [anything]
     Exit a macro, immediately returning to the caller.

     If called with an argument, exit twice, namely the current macro and the macro one level higher.  This is used to define a wrapper macro for return in trace.tmac.

Copy-in Mode
------------

When gtroff reads in the text for a macro, string, or diversion, it copies the text (including request lines, but excluding escapes) into an internal buffer. Escapes are converted into an internal form, except for \n, \$, \*, \\ and \RET, which are evaluated and inserted into the text where the escape was located. This is known as copy-in mode or copy mode.

What this means is that you can specify when these escapes are to be evaluated (either at copy-in time or at the time of use) by insulating the escapes with an extra backslash.  Compare this to the \def and \edef commands in TeX.

The following example prints the numbers 20 and 10:

     .nr x 20
     .de y
     .nr x 10
     \&\nx
     \&\\nx
     ..
     .y

Parameters
----------

The arguments to a macro or string can be examined using a variety of escapes.

 -- Register: \n[.$]
     The number of arguments passed to a macro or string.  This is a read-only number register.

     Note that the shift request can change its value.

Any individual argument can be retrieved with one of the following escapes:

 -- Escape: \\$, , n,
 -- Escape: \\$, (, nn,
 -- Escape: \\$, [, nnn, ]
     Retrieve the Nth, NNth or NNNth argument.  As usual, the first form only accepts a single number (larger than zero), the second a two-digit number (larger or equal to 10), and the third any positive integer value (larger than zero).  Macros and strings can have an unlimited number of arguments.  Note that due to copy-in mode, use two backslashes on these in actual use to prevent interpolation until the macro is actually invoked.

 -- Request: .shift, [n]
     Shift the arguments 1 position, or as many positions as specified by its argument.  After executing this request, argument I becomes argument I-N; arguments 1 to N are no longer available.  Shifting by negative amounts is currently undefined.

     The register .$ is adjusted accordingly.

 -- Escape: \\$*, , ,
 -- Escape: \\$@, , ,
     In some cases it is convenient to use all of the arguments at once (for example, to pass the arguments along to another macro).  The \$* escape concatenates all the arguments separated by spaces.  A similar escape is \$@, which concatenates all the arguments with each surrounded by double quotes, and separated by spaces.  If not in compatibility mode, the input level of double quotes is preserved (see Request and Macro Arguments).

 -- Escape: \\$^, , ,
     Handle the parameters of a macro as if they were an argument to the ds or similar requests.

          .de foo
          .  tm $1=`\\$1'
          .  tm $2=`\\$2'
          .  tm $*=`\\$*'
          .  tm $@=`\\$@'
          .  tm $^=`\\$^'
          ..
          .foo " This is a "test"
              => $1=` This is a '
              => $2=`test"'
              => $*=` This is a  test"'
              => $@=`" This is a " "test""'
              => $^=`" This is a "test"'

     This escape is useful mainly for macro packages like trace.tmac, which redefines some requests and macros for debugging purposes.

 -- Escape: \\$0, , ,
     The name used to invoke the current macro.  The als request can make a macro have more than one name.

     If a macro is called as a string (within another macro), the value of \$0 isn't changed.

          .de foo
          .  tm \\$0
          ..
          .als foo bar
          .

          .de aaa
          .  foo
          ..
          .de bbb
          .  bar
          ..
          .de ccc
          \\*[foo]\\
          ..
          .de ddd
          \\*[bar]\\
          ..
          .

          .aaa
              => foo
          .bbb
              => bar
          .ccc
              => ccc
          .ddd
              => ddd

See Request and Macro Arguments.

Page Motions
============

See Manipulating Spacing, for a discussion of the main request for vertical motion, sp.

 -- Request: .mk, [reg]
 -- Request: .rt, [dist]
     The request mk can be used to mark a location on a page, for movement to later.  This request takes a register name as an argument in which to store the current page location.  With no argument it stores the location in an internal register.  The results of this can be used later by the rt or the sp request (or the \v escape).

     The rt request returns upwards to the location marked with the last mk request.  If used with an argument, return to a position which distance from the top of the page is DIST (no previous call to mk is necessary in this case).  Default scaling indicator is v.

     If a page break occurs between a mk request and its matching rt request, the rt is silently ignored.

     Here a primitive solution for a two-column macro.

          .nr column-length 1.5i
          .nr column-gap 4m
          .nr bottom-margin 1m
          .

          .de 2c
          .  br
          .  mk
          .  ll \\n[column-length]u
          .  wh -\\n[bottom-margin]u 2c-trap
          .  nr right-side 0
          ..
          .

          .de 2c-trap
          .  ie \\n[right-side] \{\
          .    nr right-side 0
          .    po -(\\n[column-length]u + \\n[column-gap]u)
          .    \" remove trap
          .    wh -\\n[bottom-margin]u
          .  \}
          .  el \{\
          .    \" switch to right side
          .    nr right-side 1
          .    po +(\\n[column-length]u + \\n[column-gap]u)
          .    rt
          .  \}
          ..
          .

          .pl 1.5i
          .ll 4i
          This is a small test that shows how the
          rt request works in combination with mk.

          .2c
          Starting here, text is typeset in two columns.
          Note that this implementation isn't robust
          and thus not suited for a real two-column
          macro.

     Result:

          This is a small test that shows how the
          rt request works in combination with mk.

          Starting  here,    isn't    robust
          text is typeset    and   thus  not
          in two columns.    suited  for   a
          Note that  this    real two-column
          implementation     macro.

The following escapes give fine control of movements about the page.

 -- Escape: \\v, ', e, '
     Move vertically, usually from the current location on the page (if no absolute position operator | is used).  The argument E specifies the distance to move; positive is downwards and negative upwards.  The default scaling indicator for this escape is v. Beware, however, that gtroff continues text processing at the point where the motion ends, so you should always balance motions to avoid interference with text processing.

     \v doesn't trigger a trap.  This can be quite useful; for example, consider a page bottom trap macro that prints a marker in the margin to indicate continuation of a footnote or something similar.

There are some special-case escapes for vertical motion.

 -- Escape: \\r, , ,
     Move upwards 1v.

 -- Escape: \\u, , ,
     Move upwards .5v.

 -- Escape: \\d, , ,
     Move down .5v.

 -- Escape: \\h, ', e, '
     Move horizontally, usually from the current location (if no absolute position operator | is used).  The expression E indicates how far to move: positive is rightwards and negative leftwards.  The default scaling indicator for this escape is m.

     This horizontal space is not discarded at the end of a line.  To insert discardable space of a certain length use the ss request.

There are a number of special-case escapes for horizontal motion.

 -- Escape: \\SP, , ,
     An unbreakable and unpaddable (i.e. not expanded during filling) space.  (Note: This is a backslash followed by a space.)

 -- Escape: \\~, , ,
     An unbreakable space that stretches like a normal inter-word space when a line is adjusted.

 -- Escape: \\|, , ,
     A 1/6th em space.  Ignored for TTY output devices (rounded to zero).

     However, if there is a glyph defined in the current font file with name \| (note the leading backslash), the width of this glyph is used instead (even for TTYs).

 -- Escape: \\^, , ,
     A 1/12th em space.  Ignored for TTY output devices (rounded to zero).

     However, if there is a glyph defined in the current font file with name \^ (note the leading backslash), the width of this glyph is used instead (even for TTYs).

 -- Escape: \\0, , ,
     A space the size of a digit.

The following string sets the TeX logo:

     .ds TeX T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X

 -- Escape: \\w, ', text, '
 -- Register: \n[st]
 -- Register: \n[sb]
 -- Register: \n[rst]
 -- Register: \n[rsb]
 -- Register: \n[ct]
 -- Register: \n[ssc]
 -- Register: \n[skw]
     Return the width of the specified TEXT in basic units.  This allows horizontal movement based on the width of some arbitrary text (e.g. given as an argument to a macro).

          The length of the string `abc' is \w'abc'u.
              => The length of the string `abc' is 72u.

     Font changes may occur in TEXT, which don't affect current settings.

     After use, \w sets several registers:

     st
     sb
          The highest and lowest point of the baseline, respectively, in TEXT.

     rst
     rsb
          Like the st and sb registers, but takes account of the heights and depths of glyphs.  In other words, this gives the highest and lowest point of TEXT.  Values below the baseline are negative.

     ct
          Defines the kinds of glyphs occurring in TEXT:

          0
               only short glyphs, no descenders or tall glyphs.

          1
               at least one descender.

          2
               at least one tall glyph.

          3
               at least one each of a descender and a tall glyph.

     ssc
          The amount of horizontal space (possibly negative) that should be added to the last glyph before a subscript.

     skw
          How far to right of the center of the last glyph in the \w argument, the center of an accent from a roman font should be placed over that glyph.

 -- Escape: \\k, , p,
 -- Escape: \\k, (, ps,
 -- Escape: \\k, [, position, ]
     Store the current horizontal position in the input line in number register with name POSITION (one-character name P, two-character name PS).  Use this, for example, to return to the beginning of a string for highlighting or other decoration.

 -- Register: \n[hp]
     The current horizontal position at the input line.

 -- Register: \n[.k]
     A read-only number register containing the current horizontal output position (relative to the current indentation).

 -- Escape: \\o, ', abc, '
     Overstrike glyphs A, B, C, ...; the glyphs are centered, and the resulting spacing is the largest width of the affected glyphs.

 -- Escape: \\z, , g,
     Print glyph G with zero width, i.e., without spacing.  Use this to overstrike glyphs left-aligned.

 -- Escape: \\Z, ', anything, '
     Print ANYTHING, then restore the horizontal and vertical position. The argument may not contain tabs or leaders.

     The following is an example of a strike-through macro:

          .de ST
          .nr ww \w'\\$1'
          \Z@\v'-.25m'\l'\\n[ww]u'@\\$1
          ..
          .
          This is
          .ST "a test"
          an actual emergency!

Drawing Requests
================

gtroff provides a number of ways to draw lines and other figures on the page.  Used in combination with the page motion commands (see Page Motions, for more info), a wide variety of figures can be drawn.  However, for complex drawings these operations can be quite cumbersome, and it may be wise to use graphic preprocessors like gpic or ggrn.  See gpic, and ggrn, for more information.

All drawing is done via escapes.

 -- Escape: \\l, ', l, '
 -- Escape: \\l, ', lg, '
     Draw a line horizontally.  L is the length of the line to be drawn.  If it is positive, start the line at the current location and draw to the right; its end point is the new current location.  Negative values are handled differently: The line starts at the current location and draws to the left, but the current location doesn't move.

     L can also be specified absolutely (i.e. with a leading |), which draws back to the beginning of the input line.  Default scaling indicator is m.

     The optional second parameter G is a glyph to draw the line with.  If this second argument is not specified, gtroff uses the underscore glyph, \[ru].

     To separate the two arguments (to prevent gtroff from interpreting a drawing glyph as a scaling indicator if the glyph is represented by a single character) use \&.

     Here a small useful example:

          .de box
          \[br]\\$*\[br]\l'|0\[rn]'\l'|0\[ul]'
          ..

     Note that this works by outputting a box rule (a vertical line), then the text given as an argument and then another box rule.  Finally, the line drawing escapes both draw from the current location to the beginning of the input line -- this works because the line length is negative, not moving the current point.

 -- Escape: \\L, ', l, '
 -- Escape: \\L, ', lg, '
     Draw vertical lines.  Its parameters are similar to the \l escape, except that the default scaling indicator is v.  The movement is downwards for positive values, and upwards for negative values.  The default glyph is the box rule glyph, \[br].  As with the vertical motion escapes, text processing blindly continues where the line ends.

          This is a \L'3v'test.

     Here is the result, produced with grotty.

          This is a
                    |
                    |
                    |test.

 -- Escape: \\D, ', command arg ..., '
     The \D escape provides a variety of drawing functions.  Note that on character devices, only vertical and horizontal lines are supported within grotty; other devices may only support a subset of the available drawing functions.

     The default scaling indicator for all subcommands of \D is m for horizontal distances and v for vertical ones. Exceptions are \D'f ...' and \D't ...', which use u as the default, and \D'FX ...', which arguments are treated similar to the defcolor request.

     \D'l DX DY'
          Draw a line from the current location to the relative point specified by (DX,DY), where positive values mean right and down, respectively.  The end point of the line is the new current location.

          The following example is a macro for creating a box around a text string; for simplicity, the box margin is taken as a fixed value, 0.2m.

               .de BOX
               .  nr @wd \w'\\$1'
               \h'.2m'\
               \h'-.2m'\v'(.2m - \\n[rsb]u)'\
               \D'l 0 -(\\n[rst]u - \\n[rsb]u + .4m)'\
               \D'l (\\n[@wd]u + .4m) 0'\
               \D'l 0 (\\n[rst]u - \\n[rsb]u + .4m)'\
               \D'l -(\\n[@wd]u + .4m) 0'\
               \h'.2m'\v'-(.2m - \\n[rsb]u)'\
               \\$1\
               \h'.2m'
               ..

          First, the width of the string is stored in register @wd.  Then, four lines are drawn to form a box, properly offset by the box margin. The registers rst and rsb are set by the \w escape, containing the largest height and depth of the whole string.

     \D'c D'
          Draw a circle with a diameter of D with the leftmost point at the current position.  After drawing, the current location is positioned at the rightmost point of the circle.

     \D'C D'
          Draw a solid circle with the same parameters and behaviour as an outlined circle.  No outline is drawn.

     \D'e X Y'
          Draw an ellipse with a horizontal diameter of X and a vertical diameter of Y with the leftmost point at the current position. After drawing, the current location is positioned at the rightmost point of the ellipse.

     \D'E X Y'
          Draw a solid ellipse with the same parameters and behaviour as an outlined ellipse.  No outline is drawn.

     \D'a DX1 DY1 DX2 DY2'
          Draw an arc clockwise from the current location through the two specified relative locations (DX1,DY1) and (DX2,DY2).  The coordinates of the first point are relative to the current position, and the coordinates of the second point are relative to the first point.  After drawing, the current position is moved to the final point of the arc.

     \D'~ DX1 DY1 DX2 DY2 ...'
          Draw a spline from the current location to the relative point (DX1,DY1) and then to (DX2,DY2), and so on.  The current position is moved to the terminal point of the drawn curve.

     \D'f N'
          Set the shade of gray to be used for filling solid objects to N; N must be an integer between 0 and 1000, where 0 corresponds solid white and 1000 to solid black, and values in between correspond to intermediate shades of gray.  This applies only to solid circles, solid ellipses, and solid polygons.  By default, a level of 1000 is used.

          Despite of being silly, the current point is moved horizontally to the right by N.

          Don't use this command!  It has the serious drawback that it is always rounded to the next integer multiple of the horizontal resolution (the value of the hor keyword in the DESC file).  Use \M (see Colors) or \D'Fg ...' instead.

     \D'p DX1 DY1 DX2 DY2 ...'
          Draw a polygon from the current location to the relative position (DX1,DY1) and then to (DX2,DY2) and so on.  When the specified data points are exhausted, a line is drawn back to the starting point.  The current position is changed by adding the sum of all arguments with odd index to the actual horizontal position and the even ones to the vertical position.

     \D'P DX1 DY1 DX2 DY2 ...'
          Draw a solid polygon with the same parameters and behaviour as an outlined polygon.  No outline is drawn.

          Here a better variant of the box macro to fill the box with some color. Note that the box must be drawn before the text since colors in gtroff are not transparent; the filled polygon would hide the text completely.

               .de BOX
               .  nr @wd \w'\\$1'
               \h'.2m'\
               \h'-.2m'\v'(.2m - \\n[rsb]u)'\
               \M[lightcyan]\
               \D'P 0 -(\\n[rst]u - \\n[rsb]u + .4m) \
                    (\\n[@wd]u + .4m) 0 \
                    0 (\\n[rst]u - \\n[rsb]u + .4m) \
                    -(\\n[@wd]u + .4m) 0'\
               \h'.2m'\v'-(.2m - \\n[rsb]u)'\
               \M[]\
               \\$1\
               \h'.2m'
               ..

          If you want a filled polygon that has exactly the same size as an unfilled one, you must draw both an unfilled and a filled polygon.  A filled polygon is always smaller than an unfilled one because the latter uses straight lines with a given line thickness to connect the polygon's corners, while the former simply fills the area defined by the coordinates.

               \h'1i'\v'1i'\
               \# increase line thickness
               \Z'\D't 5p''\
               \# draw unfilled polygon
               \Z'\D'p 3 3 -6 0''\
               \# draw filled polygon
               \Z'\D'P 3 3 -6 0''

     \D't N'
          Set the current line thickness to N machine units.  A value of zero selects the smallest available line thickness.  A negative value makes the line thickness proportional to the current point size (this is the default behaviour of AT&T troff).

          Despite of being silly, the current point is moved horizontally to the right by N.

     \D'FSCHEME COLOR_COMPONENTS'
          Change current fill color.  SCHEME is a single letter denoting the color scheme: r (rgb), c (cmy), k (cmyk), g (gray), or d (default color).  The color components use exactly the same syntax as in the defcolor request (see Colors); the command \D'Fd' doesn't take an argument.

          No position changing!

          Examples:

               \D'Fg .3'      \" same gray as \D'f 700'
               \D'Fr #0000ff' \" blue

See Graphics Commands.

 -- Escape: \\b, ', string, '
     Pile a sequence of glyphs vertically, and center it vertically on the current line.  Use it to build large brackets and braces.

     Here an example how to create a large opening brace:

          \b'\[lt]\[bv]\[lk]\[bv]\[lb]'

     The first glyph is on the top, the last glyph in STRING is at the bottom.  Note that gtroff separates the glyphs vertically by 1m, and the whole object is centered 0.5m above the current baseline; the largest glyph width is used as the width for the whole object.  This rather unflexible positioning algorithm doesn't work with -Tdvi since the bracket pieces vary in height for this device. Instead, use the eqn preprocessor.

     See Manipulating Spacing, how to adjust the vertical spacing with the \x escape.

Traps
=====

Traps are locations that, when reached, call a specified macro. These traps can occur at a given location on the page, at a given location in the current diversion, at a blank line, after a certain number of input lines, or at the end of input.

Setting a trap is also called planting. It is also said that a trap is sprung if the associated macro is executed.

Page Location Traps
-------------------

Page location traps perform an action when gtroff reaches or passes a certain vertical location on the page.  Page location traps have a variety of purposes, including:

  * setting headers and footers

  * setting body text in multiple columns

  * setting footnotes

 -- Request: .vpt, flag
 -- Register: \n[.vpt]
     Enable vertical position traps if FLAG is non-zero, or disables them otherwise.  Vertical position traps are traps set by the wh or dt requests.  Traps set by the it request are not vertical position traps.  The parameter that controls whether vertical position traps are enabled is global.  Initially vertical position traps are enabled.  The current setting of this is available in the .vpt read-only number register.

     Note that a page can't be ejected if vpt is set to zero.

 -- Request: .wh, dist [macro]
     Set a page location trap.  Non-negative values for DIST set the trap relative to the top of the page; negative values set the trap relative to the bottom of the page.  Default scaling indicator is v; values of DIST are always rounded to be multiples of the vertical resolution (as given in register .V).

     MACRO is the name of the macro to execute when the trap is sprung. If MACRO is missing, remove the first trap (if any) at DIST.

     The following is a simple example of how many macro packages set headers and footers.

          .de hd                \" Page header
          '  sp .5i
          .  tl 'Title''date'
          '  sp .3i
          ..
          .
          .de fo                \" Page footer
          '  sp 1v
          .  tl ''%''
          '  bp
          ..
          .
          .wh 0   hd            \" trap at top of the page
          .wh -1i fo            \" trap one inch from bottom

     A trap at or below the bottom of the page is ignored; it can be made active by either moving it up or increasing the page length so that the trap is on the page.

     Negative trap values always use the current page length; they are not converted to an absolute vertical position:

          .pl 5i
          .wh -1i xx
          .ptr
              => xx      -240
          .pl 100i
          .ptr
              => xx      -240

     It is possible to have more than one trap at the same location; to do so, the traps must be defined at different locations, then moved together with the ch request; otherwise the second trap would replace the first one.  Earlier defined traps hide later defined traps if moved to the same position (the many empty lines caused by the bp request are omitted in the following example):

          .de a
          .  nop a
          ..
          .de b
          .  nop b
          ..
          .de c
          .  nop c
          ..
          .
          .wh 1i a
          .wh 2i b
          .wh 3i c
          .bp
              => a b c

          .ch b 1i
          .ch c 1i
          .bp
              => a

          .ch a 0.5i
          .bp
              => a b

 -- Register: \n[.t]
     A read-only number register holding the distance to the next trap.

     If there are no traps between the current position and the bottom of the page, it contains the distance to the page bottom.  In a diversion, the distance to the page bottom is infinite (the returned value is the biggest integer that can be represented in groff) if there are no diversion traps.

 -- Request: .ch, macro [dist]
     Change the location of a trap.  The first argument is the name of the macro to be invoked at the trap, and the second argument is the new location for the trap (note that the parameters are specified in opposite order as in the wh request).  This is useful for building up footnotes in a diversion to allow more space at the bottom of the page for them.

     Default scaling indicator for DIST is v.  If DIST is missing, the trap is removed.

 -- Register: \n[.ne]
     The read-only number register .ne contains the amount of space that was needed in the last ne request that caused a trap to be sprung.  Useful in conjunction with the .trunc register. See Page Control, for more information.

     Since the .ne register is only set by traps it doesn't make much sense to use it outside of trap macros.

 -- Register: \n[.trunc]
     A read-only register containing the amount of vertical space truncated from an sp request by the most recently sprung vertical position trap, or, if the trap was sprung by an ne request, minus the amount of vertical motion produced by the ne request.  In other words, at the point a trap is sprung, it represents the difference of what the vertical position would have been but for the trap, and what the vertical position actually is.

     Since the .trunc register is only set by traps it doesn't make much sense to use it outside of trap macros.

 -- Register: \n[.pe]
     A read-only register that is set to 1 while a page is ejected with the bp request (or by the end of input).

     Outside of traps this register is always zero.  In the following example, only the second call to x is caused by bp.

          .de x
          \&.pe=\\n[.pe]
          .br
          ..
          .wh 1v x
          .wh 4v x
          A line.
          .br
          Another line.
          .br
              => A line.
                 .pe=0
                 Another line.

                 .pe=1

An important fact to consider while designing macros is that diversions and traps do not interact normally.  For example, if a trap invokes a header macro (while outputting a diversion) that tries to change the font on the current page, the effect is not visible before the diversion has completely been printed (except for input protected with \! or \?) since the data in the diversion is already formatted.  In most cases, this is not the expected behaviour.

Diversion Traps
---------------

 -- Request: .dt, [dist macro]
     Set a trap within a diversion.  DIST is the location of the trap (identical to the wh request; default scaling indicator is v) and MACRO is the name of the macro to be invoked.  If called without arguments, the diversion trap is removed.

     Note that there exists only a single diversion trap.

     The number register .t still works within diversions. See Diversions, for more information.

Input Line Traps
----------------

 -- Request: .it, n macro
 -- Request: .itc, n macro
     Set an input line trap.  N is the number of lines of input that may be read before springing the trap, MACRO is the macro to be invoked.  Request lines are not counted as input lines.

     For example, one possible use is to have a macro that prints the next N lines in a bold font.

          .de B
          .  it \\$1 B-end
          .  ft B
          ..
          .
          .de B-end
          .  ft R
          ..

     The itc request is identical except that an interrupted text line (ending with \c) is not counted as a separate line.

     Both requests are associated with the current environment (see Environments); switching to another environment disables the current input trap, and going back reactivates it, restoring the number of already processed lines.

Blank Line Traps
----------------

 -- Request: .blm, macro
     Set a blank line trap.  gtroff executes MACRO when it encounters a blank line in the input file.

Leading Spaces Traps
--------------------

 -- Request: .lsm, macro
 -- Register: \n[lsn]
 -- Register: \n[lss]
     Set a leading spaces trap.  gtroff executes MACRO when it encounters leading spaces in an input line; the implicit line break that normally happens in this case is suppressed.  A line consisting of spaces only, however, is treated as an empty line, possibly subject to an empty line macro set with the blm request.

     Leading spaces are removed from the input line before calling the leading spaces macro.  The number of removed spaces is stored in register lsn; the horizontal space that would be emitted if there was no leading space macro is stored in register lss. Note that lsn and lss are available even if no leading space macro has been set.

     The first thing a leading space macro sees is a token.  However, some escapes like \f or \m are handled on the fly (see Gtroff Internals, for a complete list) without creating a token at all.  Consider that a line starts with two spaces followed by \fIfoo.  While skipping the spaces \fI is handled too so that groff's current font is properly set to I, but the leading space macro only sees foo, without the preceding \fI. If the macro should see the font escape you have to `protect' it with something that creates a token, for example with \&\fIfoo.

End-of-input Traps
------------------

 -- Request: .em, macro
     Set a trap at the end of input.  MACRO is executed after the last line of the input file has been processed.

     For example, if the document had to have a section at the bottom of the last page for someone to approve it, the em request could be used.

          .de approval
          \c
          .  ne 3v
          .  sp (\\n[.t]u - 3v)
          .  in +4i
          .  lc _
          .  br
          Approved:\t\a
          .  sp
          Date:\t\t\a
          ..
          .
          .em approval

     The \c in the above example needs explanation.  For historical reasons (and for compatibility with AT&T troff), the end macro exits as soon as it causes a page break and no remaining data is in the partially collected line.

     Let us assume that there is no \c in the above approval macro, and that the page is full and has been ended with, say, a br request.  The ne request now causes the start of a new page, which in turn makes troff exit immediately for the reasons just described.  In most situations this is not intended.

     To always force processing the whole end macro independently of this behaviour it is thus advisable to insert something that starts an empty partially filled line (\c) whenever there is a chance that a page break can happen.  In the above example, the call of the ne request assures that the remaining code stays on the same page, so we have to insert \c only once.

     The next example shows how to append three lines, then starting a new page unconditionally.  Since .ne 1 doesn't give the desired effect -- there is always one line available or we are already at the beginning of the next page -- we temporarily increase the page length by one line so that we can use .ne 2.

          .de EM
          .pl +1v
          \c
          .ne 2
          line one
          .br
          \c
          .ne 2
          line two
          .br
          \c
          .ne 2
          line three
          .br
          .pl -1v
          \c
          'bp
          ..
          .em EM

     Note that this specific feature affects only the first potential page break caused by the end macro; further page breaks emitted by the end macro are handled normally.

     Another possible use of the em request is to make gtroff emit a single large page instead of multiple pages.  For example, one may want to produce a long plain-text file for reading on-screen.  The idea is to set the page length at the beginning of the document to a very large value to hold all the text, and automatically adjust it to the exact height of the document after the text has been output.

          .de adjust-page-length
          .  br
          .  pl \\n[nl]u \" \n[nl] holds the current vert. position
          ..
          .
          .de single-page-mode
          .  pl 99999
          .  em adjust-page-length
          ..
          .
          .\" activate the above code
          .single-page-mode

     Since only one end-of-input trap does exist and other macro packages may already use it, care must be taken not to break the mechanism.  A simple solution would be to append the above macro to the macro package's end-of-input macro using the .am request.

Diversions
==========

In gtroff it is possible to divert text into a named storage area.  Due to the similarity to defining macros it is sometimes said to be stored in a macro.  This is used for saving text for output at a later time, which is useful for keeping blocks of text on the same page, footnotes, tables of contents, and indices.

For orthogonality it is said that gtroff is in the top-level diversion if no diversion is active (i.e., the data is diverted to the output device).

Although the following requests can be used to create diversions, simply using an undefined diversion will cause it to be defined as empty. See Identifiers.

 -- Request: .di, macro
 -- Request: .da, macro
     Begin a diversion.  Like the de request, it takes an argument of a macro name to divert subsequent text into.  The da macro appends to an existing diversion.

     di or da without an argument ends the diversion.

     The current partially filled line is included into the diversion.  See the box request below for an example.  Note that switching to another (empty) environment (with the ev request) avoids the inclusion of the current partially filled line.

 -- Request: .box, macro
 -- Request: .boxa, macro
     Begin (or append to) a diversion like the di and da requests.  The difference is that box and boxa do not include a partially filled line in the diversion.

     Compare this:

          Before the box.
          .box xxx
          In the box.
          .br
          .box
          After the box.
          .br
              => Before the box.  After the box.
          .xxx
              => In the box.

     with this:

          Before the diversion.
          .di yyy
          In the diversion.
          .br
          .di
          After the diversion.
          .br
              => After the diversion.
          .yyy
              => Before the diversion.  In the diversion.

     box or boxa without an argument ends the diversion.

 -- Register: \n[.z]
 -- Register: \n[.d]
     Diversions may be nested.  The read-only number register .z contains the name of the current diversion (this is a string-valued register).  The read-only number register .d contains the current vertical place in the diversion.  If not in a diversion it is the same as register nl.

 -- Register: \n[.h]
     The high-water mark on the current page or in the current diversion.  It corresponds to the text baseline of the lowest line on the page.  This is a read-only register.

          .tm .h==\n[.h], nl==\n[nl]
              => .h==0, nl==-1
          This is a test.
          .br
          .sp 2
          .tm .h==\n[.h], nl==\n[nl]
              => .h==40, nl==120

     As can be seen in the previous example, empty lines are not considered in the return value of the .h register.

 -- Register: \n[dn]
 -- Register: \n[dl]
     After completing a diversion, the read-write number registers dn and dl contain the vertical and horizontal size of the diversion. Note that only the just processed lines are counted: For the computation of dn and dl, the requests da and boxa are handled as if di and box had been used -- lines that have been already stored in a macro are not taken into account.

          .\" Center text both horizontally & vertically
          .
          .\" Enclose macro definitions in .eo and .ec
          .\" to avoid the doubling of the backslash
          .eo
          .\" macro .(c starts centering mode
          .de (c
          .  br
          .  ev (c
          .  evc 0
          .  in 0
          .  nf
          .  di @c
          ..

          .\" macro .)c terminates centering mode
          .de )c
          .  br
          .  ev
          .  di
          .  nr @s (((\n[.t]u - \n[dn]u) / 2u) - 1v)
          .  sp \n[@s]u
          .  ce 1000
          .  @c
          .  ce 0
          .  sp \n[@s]u
          .  br
          .  fi
          .  rr @s
          .  rm @c
          ..
          .\" End of macro definitions, restore escape mechanism
          .ec

 -- Escape: \\!, , ,
 -- Escape: \\?, , anything, \\?
     Prevent requests, macros, and escapes from being interpreted when read into a diversion.  Both escapes take the given text and transparently embed it into the diversion.  This is useful for macros that shouldn't be invoked until the diverted text is actually output.

     The \! escape transparently embeds text up to and including the end of the line.  The \? escape transparently embeds text until the next occurrence of the \? escape.  Example:

          \?ANYTHING\?

     ANYTHING may not contain newlines; use \!  to embed newlines in a diversion.  The escape sequence \? is also recognized in copy mode and turned into a single internal code; it is this code that terminates ANYTHING.  Thus the following example prints 4.

          .nr x 1
          .nf
          .di d
          \?\\?\\\\?\\\\\\\\nx\\\\?\\?\?
          .di
          .nr x 2
          .di e
          .d
          .di
          .nr x 3
          .di f
          .e
          .di
          .nr x 4
          .f

     Both escapes read the data in copy mode.

     If \! is used in the top-level diversion, its argument is directly embedded into the gtroff intermediate output.  This can be used for example to control a postprocessor that processes the data before it is sent to the device driver.

     The \? escape used in the top-level diversion produces no output at all; its argument is simply ignored.

 -- Request: .output, string
     Emit STRING directly to the gtroff intermediate output (subject to copy mode interpretation); this is similar to \! used at the top level.  An initial double quote in STRING is stripped off to allow initial blanks.

     This request can't be used before the first page has started -- if you get an error, simply insert .br before the output request.

     Without argument, output is ignored.

     Use with caution!  It is normally only needed for mark-up used by a postprocessor that does something with the output before sending it to the output device, filtering out STRING again.

 -- Request: .asciify, div
     Unformat the diversion specified by DIV in such a way that ASCII characters, characters translated with the trin request, space characters, and some escape sequences that were formatted and diverted are treated like ordinary input characters when the diversion is reread.  It can be also used for gross hacks; for example, the following sets register n to 1.

          .tr @.
          .di x
          @nr n 1
          .br
          .di
          .tr @@
          .asciify x
          .x

     Note that asciify cannot return all items in a diversion back to their source equivalent, nodes such as \N[...] will still remain as nodes, so the result cannot be guaranteed to be a pure string.

     See Copy-in Mode.

 -- Request: .unformat, div
     Like asciify, unformat the specified diversion.  However, unformat only unformats spaces and tabs between words. Unformatted tabs are treated as input tokens, and spaces are stretchable again.

     The vertical size of lines is not preserved; glyph information (font, font size, space width, etc.) is retained.

Environments
============

It happens frequently that some text should be printed in a certain format regardless of what may be in effect at the time, for example, in a trap invoked macro to print headers and footers.  To solve this gtroff processes text in environments.  An environment contains most of the parameters that control text processing.  It is possible to switch amongst these environments; by default gtroff processes text in environment 0.  The following is the information kept in an environment.

  * font parameters (size, family, style, glyph height and slant, space and sentence space size)

  * page parameters (line length, title length, vertical spacing, line spacing, indentation, line numbering, centering, right-justifying, underlining, hyphenation data)

  * fill and adjust mode

  * tab stops, tab and leader characters, escape character, no-break and hyphen indicators, margin character data

  * partially collected lines

  * input traps

  * drawing and fill colours

These environments may be given arbitrary names (see Identifiers, for more info).  Old versions of troff only had environments named 0, 1, and 2.

 -- Request: .ev, [env]
 -- Register: \n[.ev]
     Switch to another environment.  The argument ENV is the name of the environment to switch to.  With no argument, gtroff switches back to the previous environment.  There is no limit on the number of named environments; they are created the first time that they are referenced.  The .ev read-only register contains the name or number of the current environment.  This is a string-valued register.

     Note that a call to ev (with argument) pushes the previously active environment onto a stack.  If, say, environments foo, bar, and zap are called (in that order), the first ev request without parameter switches back to environment bar (which is popped off the stack), and a second call switches back to environment foo.

     Here is an example:

          .ev footnote-env
          .fam N
          .ps 6
          .vs 8
          .ll -.5i
          .ev

          ...

          .ev footnote-env
          \(dg Note the large, friendly letters.
          .ev

 -- Request: .evc, env
     Copy the environment ENV into the current environment.

     The following environment data is not copied:

       * Partially filled lines.

       * The status whether the previous line was interrupted.

       * The number of lines still to center, or to right-justify, or to underline (with or without underlined spaces); they are set to zero.

       * The status whether a temporary indentation is active.

       * Input traps and its associated data.

       * Line numbering mode is disabled; it can be reactivated with .nm +0.

       * The number of consecutive hyphenated lines (set to zero).

 -- Register: \n[.w]
 -- Register: \n[.cht]
 -- Register: \n[.cdp]
 -- Register: \n[.csk]
     The \n[.w] register contains the width of the last glyph added to the current environment.

     The \n[.cht] register contains the height of the last glyph added to the current environment.

     The \n[.cdp] register contains the depth of the last glyph added to the current environment.  It is positive for glyphs extending below the baseline.

     The \n[.csk] register contains the skew (how far to the right of the glyph's center that gtroff should place an accent) of the last glyph added to the current environment.

 -- Register: \n[.n]
     The \n[.n] register contains the length of the previous output line in the current environment.

Suppressing output
==================

 -- Escape: \\O, , num,
     Disable or enable output depending on the value of NUM:

     \O0
          Disable any glyphs from being emitted to the device driver, provided that the escape occurs at the outer level (see \O[3] and \O[4]).  Motion is not suppressed so effectively \O[0] means pen up.

     \O1
          Enable output of glyphs, provided that the escape occurs at the outer level.

     \O0 and \O1 also reset the four registers opminx, opminy, opmaxx, and opmaxy to -1. See Register Index.  These four registers mark the top left and bottom right hand corners of a box that encompasses all written glyphs.

     For example the input text:

          Hello \O[0]world \O[1]this is a test.

     produces the following output:

          Hello       this is a test.

     \O2
          Provided that the escape occurs at the outer level, enable output of glyphs and also write out to stderr the page number and four registers encompassing the glyphs previously written since the last call to \O.

     \O3
          Begin a nesting level.  At start-up, gtroff is at outer level. The current level is contained within the read-only register .O. See Built-in Registers.

     \O4
          End a nesting level.  The current level is contained within the read-only register .O.  See Built-in Registers.

     \O[5PFILENAME]
          This escape is grohtml specific.  Provided that this escape occurs at the outer nesting level write the filename to stderr.  The position of the image, P, must be specified and must be one of l, r, c, or i (left, right, centered, inline).  FILENAME is associated with the production of the next inline image.

Colors
======

 -- Request: .color, [n]
 -- Register: \n[.color]
     If N is missing or non-zero, activate colors (this is the default); otherwise, turn it off.

     The read-only number register .color is 1 if colors are active, 0 otherwise.

     Internally, color sets a global flag; it does not produce a token.  Similar to the cp request, you should use it at the beginning of your document to control color output.

     Colors can be also turned off with the -c command-line option.

 -- Request: .defcolor, ident scheme color_components
     Define color with name IDENT.  SCHEME can be one of the following values: rgb (three components), cmy (three components), cmyk (four components), and gray or grey (one component).

     Color components can be given either as a hexadecimal string or as positive decimal integers in the range 0--65535.  A hexadecimal string contains all color components concatenated.  It must start with either # or ##; the former specifies hex values in the range 0--255 (which are internally multiplied by 257), the latter in the range 0--65535.  Examples: #FFC0CB (pink), ##ffff0000ffff (magenta).  The default color name default can't be redefined; its value is device-specific (usually black).  It is possible that the default color for \m and \M is not identical.

     A new scaling indicator f has been introduced, which multiplies its value by 65536; this makes it convenient to specify color components as fractions in the range 0 to 1 (1f equals 65536u). Example:

          .defcolor darkgreen rgb 0.1f 0.5f 0.2f

     Note that f is the default scaling indicator for the defcolor request, thus the above statement is equivalent to

          .defcolor darkgreen rgb 0.1 0.5 0.2

 -- Request: .gcolor, [color]
 -- Escape: \\m, , c,
 -- Escape: \\m, (, co,
 -- Escape: \\m, [, color, ]
 -- Register: \n[.m]
     Set (glyph) drawing color.  The following examples show how to turn the next four words red.

          .gcolor red
          these are in red
          .gcolor
          and these words are in black.

          \m[red]these are in red\m[] and these words are in black.

     The escape \m[] returns to the previous color, as does a call to gcolor without an argument.

     The name of the current drawing color is available in the read-only, string-valued number register .m.

     The drawing color is associated with the current environment (see Environments).

     Note that \m doesn't produce an input token in gtroff.  As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the color on the fly:

          .mc \m[red]x\m[]

 -- Request: .fcolor, [color]
 -- Escape: \\M, , c,
 -- Escape: \\M, (, co,
 -- Escape: \\M, [, color, ]
 -- Register: \n[.M]
     Set fill (background) color for filled objects drawn with the \D'...' commands.

     A red ellipse can be created with the following code:

          \M[red]\h'0.5i'\D'E 2i 1i'\M[]

     The escape \M[] returns to the previous fill color, as does a call to fcolor without an argument.

     The name of the current fill (background) color is available in the read-only, string-valued number register .M.

     The fill color is associated with the current environment (see Environments).

     Note that \M doesn't produce an input token in gtroff.

I/O
===

gtroff has several requests for including files:

 -- Request: .so, file
     Read in the specified FILE and includes it in place of the so request.  This is quite useful for large documents, e.g. keeping each chapter in a separate file.  See gsoelim, for more information.

     Since gtroff replaces the so request with the contents of file, it makes a difference whether the data is terminated with a newline or not: Assuming that file xxx contains the word foo without a final newline, this

          This is
          .so xxx
          bar

     yields This is foobar.

     The search path for FILE can be controlled with the -I command-line option.

 -- Request: .pso, command
     Read the standard output from the specified COMMAND and includes it in place of the pso request.

     This request causes an error if used in safer mode (which is the default).  Use groff's or troff's -U option to activate unsafe mode.

     The comment regarding a final newline for the so request is valid for pso also.

 -- Request: .mso, file
     Identical to the so request except that gtroff searches for the specified FILE in the same directories as macro files for the -m command-line option. If the file name to be included has the form NAME.tmac and it isn't found, mso tries to include tmac.NAME and vice versa. If the file does not exist, a warning of type file is emitted. See Debugging, for information about warnings.

 -- Request: .trf, file
 -- Request: .cf, file
     Transparently output the contents of FILE.  Each line is output as if it were preceded by \!; however, the lines are not subject to copy mode interpretation.  If the file does not end with a newline, then a newline is added (trf only).  For example, to define a macro x containing the contents of file f, use

          .ev 1
          .di x
          .trf f
          .di
          .ev

     The calls to ev prevent that the current partial input line becomes part of the diversion.

     Both trf and cf, when used in a diversion, embeds an object in the diversion which, when reread, causes the contents of FILE to be transparently copied through to the output.  In Unix troff, the contents of FILE is immediately copied through to the output regardless of whether there is a current diversion; this behaviour is so anomalous that it must be considered a bug.

     While cf copies the contents of FILE completely unprocessed, trf disallows characters such as NUL that are not valid gtroff input characters (see Identifiers).

     For cf, within a diversion, `completely unprocessed' means that each line of a file to be inserted is handled as if it were preceded by \!\\!.

     Both requests cause a line break.

 -- Request: .nx, [file]
     Force gtroff to continue processing of the file specified as an argument.  If no argument is given, immediately jump to the end of file.

 -- Request: .rd, [prompt [arg1 arg2 ...]]
     Read from standard input, and include what is read as though it were part of the input file.  Text is read until a blank line is encountered.

     If standard input is a TTY input device (keyboard), write PROMPT to standard error, followed by a colon (or send BEL for a beep if no argument is given).

     Arguments after PROMPT are available for the input.  For example, the line

          .rd data foo bar

     with the input This is \$2. prints

          This is bar.

Using the nx and rd requests, it is easy to set up form letters.  The form letter template is constructed like this, putting the following lines into a file called repeat.let:

     .ce
     \*(td
     .sp 2
     .nf
     .rd
     .sp
     .rd
     .fi
     Body of letter.
     .bp
     .nx repeat.let

When this is run, a file containing the following lines should be redirected in.  Note that requests included in this file are executed as though they were part of the form letter.  The last block of input is the ex request, which tells groff to stop processing.  If this was not there, groff would not know when to stop.

     Trent A. Fisher
     708 NW 19th Av., #202
     Portland, OR  97209

     Dear Trent,

     Len Adollar
     4315 Sierra Vista
     San Diego, CA  92103

     Dear Mr. Adollar,

     .ex

 -- Request: .pi, pipe
     Pipe the output of gtroff to the shell command(s) specified by PIPE.  This request must occur before gtroff has a chance to print anything.

     pi causes an error if used in safer mode (which is the default). Use groff's or troff's -U option to activate unsafe mode.

     Multiple calls to pi are allowed, acting as a chain.  For example,

          .pi foo
          .pi bar
          ...

     is the same as .pi foo | bar.

     Note that the intermediate output format of gtroff is piped to the specified commands.  Consequently, calling groff without the -Z option normally causes a fatal error.

 -- Request: .sy, cmds
 -- Register: \n[systat]
     Execute the shell command(s) specified by CMDS.  The output is not saved anyplace, so it is up to the user to do so.

     This request causes an error if used in safer mode (which is the default).  Use groff's or troff's -U option to activate unsafe mode.

     For example, the following code fragment introduces the current time into a document:

          .sy perl -e 'printf ".nr H %d\\n.nr M %d\\n.nr S %d\\n",\
                       (localtime(time))[2,1,0]' > /tmp/x\n[$$]
          .so /tmp/x\n[$$]
          .sy rm /tmp/x\n[$$]
          \nH:\nM:\nS

     Note that this works by having the perl script (run by sy) print out the nr requests that set the number registers H, M, and S, and then reads those commands in with the so request.

     For most practical purposes, the number registers seconds, minutes, and hours, which are initialized at start-up of gtroff, should be sufficient.  Use the af request to get a formatted output:

          .af hours 00
          .af minutes 00
          .af seconds 00
          \n[hours]:\n[minutes]:\n[seconds]

     The systat read-write number register contains the return value of the system() function executed by the last sy request.

 -- Request: .open, stream file
 -- Request: .opena, stream file
     Open the specified FILE for writing and associates the specified STREAM with it.

     The opena request is like open, but if the file exists, append to it instead of truncating it.

     Both open and opena cause an error if used in safer mode (which is the default).  Use groff's or troff's -U option to activate unsafe mode.

 -- Request: .write, stream data
 -- Request: .writec, stream data
     Write to the file associated with the specified STREAM.  The stream must previously have been the subject of an open request.  The remainder of the line is interpreted as the ds request reads its second argument: A leading " is stripped, and it is read in copy-in mode.

     The writec request is like write, but only write appends a newline to the data.

 -- Request: .writem, stream xx
     Write the contents of the macro or string XX to the file associated with the specified STREAM.

     XX is read in copy mode, i.e., already formatted elements are ignored.  Consequently, diversions must be unformatted with the asciify request before calling writem.  Usually, this means a loss of information.

 -- Request: .close, stream
     Close the specified STREAM; the stream is no longer an acceptable argument to the write request.

     Here a simple macro to write an index entry.

          .open idx test.idx
          .
          .de IX
          .  write idx \\n[%] \\$*
          ..
          .
          .IX test entry
          .
          .close idx

 -- Escape: \\V, , e,
 -- Escape: \\V, (, ev,
 -- Escape: \\V, [, env, ]
     Interpolate the contents of the specified environment variable ENV (one-character name E, two-character name EV) as returned by the function getenv.  \V is interpreted in copy-in mode.

Postprocessor Access
====================

There are two escapes that give information directly to the postprocessor.  This is particularly useful for embedding POSTSCRIPT into the final document.

 -- Request: .device, xxx
 -- Escape: \\X, ', xxx, '
     Embeds its argument into the gtroff output preceded with x X.

     The escapes \&, \), \%, and \: are ignored within \X, \  and \~ are converted to single space characters.  All other escapes (except \\, which produces a backslash) cause an error.

     Contrary to \X, the device request simply processes its argument in copy mode (see Copy-in Mode).

     If the use_charnames_in_special keyword is set in the DESC file, special characters no longer cause an error; they are simply output verbatim.  Additionally, the backslash is represented as \\.

     use_charnames_in_special is currently used by grohtml only.

 -- Request: .devicem, xx
 -- Escape: \\Y, , n,
 -- Escape: \\Y, (, nm,
 -- Escape: \\Y, [, name, ]
     This is approximately equivalent to \X'\*[NAME]' (one-character name N, two-character name NM). However, the contents of the string or macro NAME are not interpreted; also it is permitted for NAME to have been defined as a macro and thus contain newlines (it is not permitted for the argument to \X to contain newlines).  The inclusion of newlines requires an extension to the Unix troff output format, and confuses drivers that do not know about this extension (see Device Control Commands).

See Output Devices.

Miscellaneous
=============

This section documents parts of gtroff that cannot (yet) be categorized elsewhere in this manual.

 -- Request: .nm, [start [inc [space [indent]]]]
     Print line numbers.  START is the line number of the next output line.  INC indicates which line numbers are printed.  For example, the value 5 means to emit only line numbers that are multiples of 5; this defaults to 1.  SPACE is the space to be left between the number and the text; this defaults to one digit space.  The fourth argument is the indentation of the line numbers, defaulting to zero.  Both SPACE and INDENT are given as multiples of digit spaces; they can be negative also.  Without any arguments, line numbers are turned off.

     gtroff reserves three digit spaces for the line number (which is printed right-justified) plus the amount given by INDENT; the output lines are concatenated to the line numbers, separated by SPACE, and without reducing the line length.  Depending on the value of the horizontal page offset (as set with the po request), line numbers that are longer than the reserved space stick out to the left, or the whole line is moved to the right.

     Parameters corresponding to missing arguments are not changed; any non-digit argument (to be more precise, any argument starting with a character valid as a delimiter for identifiers) is also treated as missing.

     If line numbering has been disabled with a call to nm without an argument, it can be reactivated with .nm +0, using the previously active line numbering parameters.

     The parameters of nm are associated with the current environment (see Environments).  The current output line number is available in the number register ln.

          .po 1m
          .ll 2i
          This test shows how line numbering works with groff.
          .nm 999
          This test shows how line numbering works with groff.
          .br
          .nm xxx 3 2
          .ll -\w'0'u
          This test shows how line numbering works with groff.
          .nn 2
          This test shows how line numbering works with groff.

     And here the result:

           This  test shows how
           line numbering works
           999 with   groff.   This
          1000 test shows how  line
          1001 numbering works with
          1002 groff.
                This test shows how
                line      numbering
           works  with  groff.
           This test shows how
          1005  line      numbering
                works with groff.

 -- Request: .nn, [skip]
     Temporarily turn off line numbering.  The argument is the number of lines not to be numbered; this defaults to 1.

 -- Request: .mc, glyph [dist]
     Print a margin character to the right of the text. (Margin character is a misnomer since it is an output glyph.)  The first argument is the glyph to be printed.  The second argument is the distance away from the right margin.  If missing, the previously set value is used; default is 10pt).  For text lines that are too long (that is, longer than the text length plus DIST), the margin character is directly appended to the lines.

     With no arguments the margin character is turned off.  If this occurs before a break, no margin character is printed.

     For compatibility with AT&T troff, a call to mc to set the margin character can't be undone immediately; at least one line gets a margin character.  Thus

          .ll 1i
          .mc \[br]
          .mc
          xxx
          .br
          xxx

     produces

          xxx        |
          xxx

     For empty lines and lines produced by the tl request no margin character is emitted.

     The margin character is associated with the current environment (see Environments).

     This is quite useful for indicating text that has changed, and, in fact, there are programs available for doing this (they are called nrchbar and changebar and can be found in any comp.sources.unix archive).

          .ll 3i
          .mc |
          This paragraph is highlighted with a margin
          character.
          .sp
          Note that vertical space isn't marked.
          .br
          \&
          .br
          But we can fake it with `\&'.

     Result:

          This  paragraph is highlighted |
          with a margin character.       |

          Note that vertical space isn't |
          marked.                        |
                                         |
          But we can fake it with `\&'.  |

 -- Request: .psbb, filename
 -- Register: \n[llx]
 -- Register: \n[lly]
 -- Register: \n[urx]
 -- Register: \n[ury]
     Retrieve the bounding box of the POSTSCRIPT image found in FILENAME.  The file must conform to Adobe's Document Structuring Conventions (DSC); the command searches for a %%BoundingBox comment and extracts the bounding box values into the number registers llx, lly, urx, and ury. If an error occurs (for example, psbb cannot find the %%BoundingBox comment), it sets the four number registers to zero.

     The search path for FILENAME can be controlled with the -I command-line option.

gtroff Internals
================

gtroff processes input in three steps.  One or more input characters are converted to an input token. (Except the escapes \f, \F, \H, \m, \M, \R, \s, and \S, which are processed immediately if not in copy-in mode.)  Then, one or more input tokens are converted to an output node.  Finally, output nodes are converted to the intermediate output language understood by all output devices.

Actually, before step one happens, gtroff converts certain escape sequences into reserved input characters (not accessible by the user); such reserved characters are used for other internal processing also -- this is the very reason why not all characters are valid input. See Identifiers, for more on this topic.

For example, the input string fi\[:u] is converted into a character token f, a character token i, and a special token :u (representing u umlaut).  Later on, the character tokens f and i are merged to a single output node representing the ligature glyph fi (provided the current font has a glyph for this ligature); the same happens with :u.  All output glyph nodes are `processed', which means that they are invariably associated with a given font, font size, advance width, etc.  During the formatting process, gtroff itself adds various nodes to control the data flow.

Macros, diversions, and strings collect elements in two chained lists: a list of input tokens that have been passed unprocessed, and a list of output nodes.  Consider the following the diversion.

     .di xxx
     a
     \!b
     c
     .br
     .di

It contains these elements.

node list                 token list   element number

line start node       ---          1
glyph node a   ---          2
word space node       ---          3
---                       b     4
---                       \n    5
glyph node c   ---          6
vertical size node    ---          7
vertical size node    ---          8
---                       \n    9

Elements 1, 7, and 8 are inserted by gtroff; the latter two (which are always present) specify the vertical extent of the last line, possibly modified by \x.  The br request finishes the current partial line, inserting a newline input token, which is subsequently converted to a space when the diversion is reread.  Note that the word space node has a fixed width that isn't stretchable anymore.  To convert horizontal space nodes back to input tokens, use the unformat request.

Macros only contain elements in the token list (and the node list is empty); diversions and strings can contain elements in both lists.

Note that the chop request simply reduces the number of elements in a macro, string, or diversion by one.  Exceptions are compatibility save and compatibility ignore input tokens, which are ignored.  The substring request also ignores those input tokens.

Some requests like tr or cflags work on glyph identifiers only; this means that the associated glyph can be changed without destroying this association.  This can be very helpful for substituting glyphs.  In the following example, we assume that glyph foo isn't available by default, so we provide a substitution using the fchar request and map it to input character x.

     .fchar \[foo] foo
     .tr x \[foo]

Now let us assume that we install an additional special font bar that has glyph foo.

     .special bar
     .rchar \[foo]

Since glyphs defined with fchar are searched before glyphs in special fonts, we must call rchar to remove the definition of the fallback glyph.  Anyway, the translation is still active; x now maps to the real glyph foo.

Macro and request arguments preserve the compatibility mode:

     .cp 1     \" switch to compatibility mode
     .de xx
     \\$1
     ..
     .cp 0     \" switch compatibility mode off
     .xx caf\['e]
         => café

Since compatibility mode is on while de is called, the macro xx activates compatibility mode while executing.  Argument $1 can still be handled properly because it inherits the compatibility mode status which was active at the point where xx is called.

After expansion of the parameters, the compatibility save and restore tokens are removed.

Debugging
=========

gtroff is not easy to debug, but there are some useful features and strategies for debugging.

 -- Request: .lf, line [filename]
     Change the line number and optionally the file name gtroff shall use for error and warning messages.  LINE is the input line number of the next line.

     Without argument, the request is ignored.

     This is a debugging aid for documents that are split into many files, then put together with soelim and other preprocessors.  Usually, it isn't invoked manually.

     Note that other troff implementations (including the original AT&T version) handle lf differently.  For them, LINE changes the line number of the current line.

 -- Request: .tm, string
 -- Request: .tm1, string
 -- Request: .tmc, string
     Send STRING to the standard error output; this is very useful for printing debugging messages among other things.

     STRING is read in copy mode.

     The tm request ignores leading spaces of STRING; tm1 handles its argument similar to the ds request: a leading double quote in STRING is stripped to allow initial blanks.

     The tmc request is similar to tm1 but does not append a newline (as is done in tm and tm1).

 -- Request: .ab, [string]
     Similar to the tm request, except that it causes gtroff to stop processing.  With no argument it prints User Abort. to standard error.

 -- Request: .ex,
     The ex request also causes gtroff to stop processing; see also I/O.

When doing something involved it is useful to leave the debugging statements in the code and have them turned on by a command-line flag.

     .if \n(DB .tm debugging output

To activate these statements say

     groff -rDB=1 file

If it is known in advance that there are many errors and no useful output, gtroff can be forced to suppress formatted output with the -z flag.

 -- Request: .pev,
     Print the contents of the current environment and all the currently defined environments (both named and numbered) on stderr.

 -- Request: .pm,
     Print the entire symbol table on stderr.  Names of all defined macros, strings, and diversions are print together with their size in bytes.  Since gtroff sometimes adds nodes by itself, the returned size can be larger than expected.

     This request differs from Unix troff: gtroff reports the sizes of diversions, ignores an additional argument to print only the total of the sizes, and the size isn't returned in blocks of 128 characters.

 -- Request: .pnr,
     Print the names and contents of all currently defined number registers on stderr.

 -- Request: .ptr,
     Print the names and positions of all traps (not including input line traps and diversion traps) on stderr.  Empty slots in the page trap list are printed as well, because they can affect the priority of subsequently planted traps.

 -- Request: .fl,
     Instruct gtroff to flush its output immediately.  The intent is for interactive use, but this behaviour is currently not implemented in gtroff.  Contrary to Unix troff, TTY output is sent to a device driver also (grotty), making it non-trivial to communicate interactively.

     This request causes a line break.

 -- Request: .backtrace,
     Print a backtrace of the input stack to the standard error stream.

     Consider the following in file test:

          .de xxx
          .  backtrace
          ..
          .de yyy
          .  xxx
          ..
          .
          .yyy

     On execution, gtroff prints the following:

          test:2: backtrace: macro `xxx'
          test:5: backtrace: macro `yyy'
          test:8: backtrace: file `test'

     The option -b of gtroff internally calls a variant of this request on each error and warning.

 -- Register: \n[slimit]
     Use the slimit number register to set the maximum number of objects on the input stack.  If slimit is less than or equal to 0, there is no limit set.  With no limit, a buggy recursive macro can exhaust virtual memory.

     The default value is 1000; this is a compile-time constant.

 -- Request: .warnscale, si
     Set the scaling indicator used in warnings to SI.  Valid values for SI are u, i, c, p, and P. At startup, it is set to i.

 -- Request: .spreadwarn, [limit]
     Make gtroff emit a warning if the additional space inserted for each space between words in an output line is larger or equal to LIMIT.  A negative value is changed to zero; no argument toggles the warning on and off without changing LIMIT.  The default scaling indicator is m.  At startup, spreadwarn is deactivated, and LIMIT is set to 3m.

     For example,

          .spreadwarn 0.2m

     causes a warning if gtroff must add 0.2m or more for each interword space in a line.

     This request is active only if text is justified to both margins (using .ad b).

gtroff has command-line options for printing out more warnings (-w) and for printing backtraces (-b) when a warning or an error occurs.  The most verbose level of warnings is -ww.

 -- Request: .warn, [flags]
 -- Register: \n[.warn]
     Control the level of warnings checked for.  The FLAGS are the sum of the numbers associated with each warning that is to be enabled; all other warnings are disabled.  The number associated with each warning is listed below.  For example, .warn 0 disables all warnings, and .warn 1 disables all warnings except that about missing glyphs.  If no argument is given, all warnings are enabled.

     The read-only number register .warn contains the current warning level.

Warnings
--------

The warnings that can be given to gtroff are divided into the following categories.  The name associated with each warning is used by the -w and -W options; the number is used by the warn request and by the .warn register.

char
1
     Non-existent glyphs. (char is a misnomer since it reports missing glyphs -- there aren't missing input characters, only invalid ones.)  This is enabled by default.

number
2
     Invalid numeric expressions.  This is enabled by default. See Expressions.

break
4
     In fill mode, lines that could not be broken so that their length was less than the line length.  This is enabled by default.

delim
8
     Missing or mismatched closing delimiters.

el
16
     Use of the el request with no matching ie request. See if-else.

scale
32
     Meaningless scaling indicators.

range
64
     Out of range arguments.

syntax
128
     Dubious syntax in numeric expressions.

di
256
     Use of di or da without an argument when there is no current diversion.

mac
512
     Use of undefined strings, macros and diversions.  When an undefined string, macro, or diversion is used, that string is automatically defined as empty.  So, in most cases, at most one warning is given for each name.

reg
1024
     Use of undefined number registers.  When an undefined number register is used, that register is automatically defined to have a value of 0. So, in most cases, at most one warning is given for use of a particular name.

tab
2048
     Use of a tab character where a number was expected.

right-brace
4096
     Use of \} where a number was expected.

missing
8192
     Requests that are missing non-optional arguments.

input
16384
     Invalid input characters.

escape
32768
     Unrecognized escape sequences.  When an unrecognized escape sequence \X is encountered, the escape character is ignored, and X is printed.

space
65536
     Missing space between a request or macro and its argument.  This warning is given when an undefined name longer than two characters is encountered, and the first two characters of the name make a defined name.  The request or macro is not invoked.  When this warning is given, no macro is automatically defined.  This is enabled by default.  This warning never occurs in compatibility mode.

font
131072
     Non-existent fonts.  This is enabled by default.

ig
262144
     Invalid escapes in text ignored with the ig request.  These are conditions that are errors when they do not occur in ignored text.

color
524288
     Color related warnings.

file
1048576
     Missing files.  The mso request gives this warning when the requested macro file does not exist.  This is enabled by default.

all
     All warnings except di, mac and reg.  It is intended that this covers all warnings that are useful with traditional macro packages.

w
     All warnings.

Implementation Differences
==========================

GNU troff has a number of features that cause incompatibilities with documents written with old versions of troff.

Long names cause some incompatibilities.  Unix troff interprets

     .dsabcd

as defining a string ab with contents cd.  Normally, GNU troff interprets this as a call of a macro named dsabcd. Also Unix troff interprets \*[ or \n[ as references to a string or number register called [.  In GNU troff, however, this is normally interpreted as the start of a long name.  In compatibility mode GNU troff interprets long names in the traditional way (which means that they are not recognized as names).

 -- Request: .cp, [n]
 -- Request: .do, cmd
 -- Register: \n[.C]
     If N is missing or non-zero, turn on compatibility mode; otherwise, turn it off.

     The read-only number register .C is 1 if compatibility mode is on, 0 otherwise.

     Compatibility mode can be also turned on with the -C command-line option.

     The do request turns off compatibility mode while executing its arguments as a gtroff command.  However, it does not turn off compatibility mode while processing the macro itself.  To do that, use the de1 request (or manipulate the .C register manually). See Writing Macros.

          .do fam T

     executes the fam request when compatibility mode is enabled.

     gtroff restores the previous compatibility setting before interpreting any files sourced by the CMD.

Two other features are controlled by -C.  If not in compatibility mode, GNU troff preserves the input level in delimited arguments:

     .ds xx '
     \w'abc\*(xxdef'

In compatibility mode, the string 72def' is returned; without -C the resulting string is 168 (assuming a TTY output device).

Finally, the escapes \f, \H, \m, \M, \R, \s, and \S are transparent for recognizing the beginning of a line only in compatibility mode (this is a rather obscure feature).  For example, the code

     .de xx
     Hello!
     ..
     \fB.xx\fP

prints Hello! in bold face if in compatibility mode, and .xx in bold face otherwise.

GNU troff does not allow the use of the escape sequences \|, \^, \&, \{, \}, \SP, \', \`, \-, \_, \!, \%, and \c in names of strings, macros, diversions, number registers, fonts or environments; Unix troff does.  The \A escape sequence (see Identifiers) may be helpful in avoiding use of these escape sequences in names.

Fractional point sizes cause one noteworthy incompatibility.  In Unix troff the ps request ignores scale indicators and thus

     .ps 10u

sets the point size to 10 points, whereas in GNU troff it sets the point size to 10 scaled points.  See Fractional Type Sizes, for more information.

In GNU troff there is a fundamental difference between (unformatted) input characters and (formatted) output glyphs. Everything that affects how a glyph is output is stored with the glyph node; once a glyph node has been constructed it is unaffected by any subsequent requests that are executed, including bd, cs, tkf, tr, or fp requests.  Normally glyphs are constructed from input characters at the moment immediately before the glyph is added to the current output line.  Macros, diversions and strings are all, in fact, the same type of object; they contain lists of input characters and glyph nodes in any combination.  A glyph node does not behave like an input character for the purposes of macro processing; it does not inherit any of the special properties that the input character from which it was constructed might have had.  For example,

     .di x
     \\\\
     .br
     .di
     .x

prints \\ in GNU troff; each pair of input backslashes is turned into one output backslash and the resulting output backslashes are not interpreted as escape characters when they are reread. Unix troff would interpret them as escape characters when they were reread and would end up printing one \.  The correct way to obtain a printable backslash is to use the \e escape sequence: This always prints a single instance of the current escape character, regardless of whether or not it is used in a diversion; it also works in both GNU troff and Unix troff. (To be completely independent of the current escape character, use \(rs, which represents a reverse solidus (backslash) glyph.)  To store, for some reason, an escape sequence in a diversion that is interpreted when the diversion is reread, either use the traditional \! transparent output facility, or, if this is unsuitable, the new \? escape sequence.

See Diversions, and Gtroff Internals, for more information.

Preprocessors
*************

This chapter describes all preprocessors that come with groff or which are freely available.

geqn
====

Invoking geqn
-------------

gtbl
====

Invoking gtbl
-------------

gpic
====

Invoking gpic
-------------

ggrn
====

Invoking ggrn
-------------

grap
====

A free implementation of grap, written by Ted Faber, is available as an extra package from the following address:

     http://www.lunabase.org/~faber/Vault/software/grap/

gchem
=====

Invoking gchem
--------------

grefer
======

Invoking grefer
---------------

gsoelim
=======

Invoking gsoelim
----------------

preconv
=======

Invoking preconv
----------------

Output Devices
**************

Special Characters
==================

See Font Files.

grotty
======

The postprocessor grotty translates the output from GNU troff into a form suitable for typewriter-like devices.  It is fully documented on its manual page, grotty(1).

Invoking grotty
---------------

The postprocessor grotty accepts the following command-line options:

-b
     Do not overstrike bold glyphs.  Ignored if -c isn't used.

-B
     Do not underline bold-italic glyphs.  Ignored if -c isn't used.

-c
     Use overprint and disable colours for printing on legacy Teletype printers (see below).

-d
     Do not render lines (that is, ignore all \D escapes).

-f
     Use form feed control characters in the output.

-FDIR
     Put the directory DIR/devNAME in front of the search path for the font and device description files, given the target device NAME.

-h
     Use horizontal tabs for sequences of 8 space characters.

-i
     Request italic glyphs from the terminal.  Ignored if -c is active.

-o
     Do not overstrike.

-r
     Highlight italic glyphs.  Ignored if -c is active.

-u
     Do not underline italic glyphs.  Ignored if -c isn't used.

-U
     Do not overstrike bold-italic glyphs.  Ignored if -c isn't used.

-v
     Print the version number.

The -c mode for TTY output devices means that underlining is done by emitting sequences of _ and ^H (the backspace character) before the actual character.  Literally, this is printing an underline character, then moving the caret back one character position, and printing the actual character at the same position as the underline character (similar to a typewriter).  Usually, a modern terminal can't interpret this (and the original Teletype machines for which this sequence was appropriate are no longer in use).  You need a pager program like less that translates this into ISO 6429 SGR sequences to control terminals.

grops
=====

The postprocessor grops translates the output from GNU troff into a form suitable for Adobe POSTSCRIPT devices.  It is fully documented on its manual page, grops(1).

Invoking grops
--------------

The postprocessor grops accepts the following command-line options:

-bFLAGS
     Use backward compatibility settings given by FLAGS as documented in the grops(1) manual page.  Overrides the command broken in the DESC file.

-cN
     Print N copies of each page.

-FDIR
     Put the directory DIR/devNAME in front of the search path for the font, prologue and device description files, given the target device NAME, usually ps.

-g
     Tell the printer to guess the page length.  Useful for printing vertically centered pages when the paper dimensions are determined at print time.

-IPATH ...
     Consider the directory PATH for searching included files specified with relative paths.  The current directory is searched as fallback.

-l
     Use landscape orientation.

-m
     Use manual feed.

-pPAPERSIZE
     Set the page dimensions.  Overrides the commands papersize, paperlength, and paperwidth in the DESC file.  See the groff_font(5) manual page for details.

-PPROLOGUE
     Use the PROLOGUE in the font path as the prologue instead of the default prologue.  Overrides the environment variable GROPS_PROLOGUE.

-wN
     Set the line thickness to N/1000em.  Overrides the default value N = 40.

-v
     Print the version number.

Embedding POSTSCRIPT
--------------------

The escape sequence

\X'ps: import FILE LLX LLY URX URY WIDTH [HEIGHT]'

places a rectangle of the specified WIDTH containing the POSTSCRIPT drawing from file FILE bound by the box from LLX LLY to URX URY (in POSTSCRIPT coordinates) at the insertion point.  If HEIGHT is not specified, the embedded drawing is scaled proportionally.

See Miscellaneous, for the psbb request, which automatically generates the bounding box.

This escape sequence is used internally by the macro PSPIC (see the groff_tmac(5) manual page).

gropdf
======

The postprocessor gropdf translates the output from GNU troff into a form suitable for Adobe PDF devices.  It is fully documented on its manual page, gropdf(1).

Invoking gropdf
---------------

The postprocessor gropdf accepts the following command-line options:

-d
     Produce uncompressed PDFs that include debugging comments.

-e
     This forces gropdf to embed all used fonts in the PDF, even if they are one of the 14 base Adobe fonts.

-FDIR
     Put the directory DIR/devNAME in front of the search path for the font, prologue and device description files, given the target device NAME, usually pdf.

-yFOUNDRY
     This forces the use of a different font foundry.

-l
     Use landscape orientation.

-pPAPERSIZE
     Set the page dimensions.  Overrides the commands papersize, paperlength, and paperwidth in the DESC file.  See the groff_font(5) manual page for details.

-v
     Print the version number.

-s
     Append a comment line to end of PDF showing statistics, i.e. number of pages in document.  Ghostscript's ps2pdf(1) complains about this line if it is included, but works anyway.

-uFILENAME
     gropdf normally includes a ToUnicode CMap with any font created using text.enc as the encoding file, this makes it easier to search for words that contain ligatures.  You can include your own CMap by specifying a FILENAME or have no CMap at all by omitting the FILENAME.

Embedding PDF
-------------

The escape sequence

\X'pdf: pdfpic FILE ALIGNMENT WIDTH [HEIGHT] [LINELENGTH]'

places a rectangle of the specified WIDTH containing the PDF drawing from file FILE of desired WIDTH and HEIGHT (if HEIGHT is missing or zero then it is scaled proportionally).  If ALIGNMENT is -L the drawing is left aligned.  If it is -C or -R a LINELENGTH greater than the width of the drawing is required as well.  If WIDTH is specified as zero then the width is scaled in proportion to the height.

grodvi
======

The postprocessor grodvi translates the output from GNU troff into the DVI output format compatible with the TeX document preparation system.  It is fully documented on its manual page, grodvi(1).

Invoking grodvi
---------------

The postprocessor grodvi accepts the following command-line options:

-d
     Do not use tpic specials to implement drawing commands.

-FDIR
     Put the directory DIR/devNAME in front of the search path for the font and device description files, given the target device NAME, usually dvi.

-l
     Use landscape orientation.

-pPAPERSIZE
     Set the page dimensions.  Overrides the commands papersize, paperlength, and paperwidth in the DESC file.  See groff_font(5) manual page for details.

-v
     Print the version number.

-wN
     Set the line thickness to N/1000em.  Overrides the default value N = 40.

grolj4
======

The postprocessor grolj4 translates the output from GNU troff into the PCL5 output format suitable for printing on a HP LaserJet 4 printer.  It is fully documented on its manual page, grolj4(1).

Invoking grolj4
---------------

The postprocessor grolj4 accepts the following command-line options:

-cN
     Print N copies of each page.

-FDIR
     Put the directory DIR/devNAME in front of the search path for the font and device description files, given the target device NAME, usually lj4.

-l
     Use landscape orientation.

-pSIZE
     Set the page dimensions.  Valid values for SIZE are: letter, legal, executive, a4, com10, monarch, c5, b5, d1.

-v
     Print the version number.

-wN
     Set the line thickness to N/1000em.  Overrides the default value N = 40.

The special drawing command \D'R DH DV' draws a horizontal rectangle from the current position to the position at offset (DH,DV).

grolbp
======

The postprocessor grolbp translates the output from GNU troff into the LBP output format suitable for printing on Canon CAPSL printers.  It is fully documented on its manual page, grolbp(1).

Invoking grolbp
---------------

The postprocessor grolbp accepts the following command-line options:

-cN
     Print N copies of each page.

-FDIR
     Put the directory DIR/devNAME in front of the search path for the font, prologue and device description files, given the target device NAME, usually lbp.

-l
     Use landscape orientation.

-oORIENTATION
     Use the ORIENTATION specified: portrait or landscape.

-pPAPERSIZE
     Set the page dimensions.  See groff_font(5) manual page for details.

-wN
     Set the line thickness to N/1000em.  Overrides the default value N = 40.

-v
     Print the version number.

-h
     Print command-line help.

grohtml
=======

The grohtml front end (which consists of a preprocessor, pre-grohtml, and a device driver, post-grohtml) translates the output of GNU troff to HTML.  Users should always invoke grohtml via the groff command with a \-Thtml option.  If no files are given, grohtml will read the standard input.  A filename of - will also cause grohtml to read the standard input.  HTML output is written to the standard output.  When grohtml is run by groff, options can be passed to grohtml using groff's -P option.

grohtml invokes groff twice.  In the first pass, pictures, equations, and tables are rendered using the ps device, and in the second pass HTML output is generated by the html device.

grohtml always writes output in UTF-8 encoding and has built-in entities for all non-composite unicode characters.  In spite of this, groff may issue warnings about unknown special characters if they can't be found during the first pass.  Such warnings can be safely ignored unless the special characters appear inside a table or equation, in which case glyphs for these characters must be defined for the ps device as well.

This output device is fully documented on its manual page, grohtml(1).

Invoking grohtml
----------------

The postprocessor grohtml accepts the following command-line options:

-aBITS
     Use this number of BITS (= 1, 2 or 4) for text antialiasing. Default: BITS = 4.

-a0
     Do not use text antialiasing.

-b
     Use white background.

-DDIR
     Store rendered images in the directory DIR.

-FDIR
     Put the directory DIR/devNAME in front of the search path for the font, prologue and device description files, given the target device NAME, usually html.

-gBITS
     Use this number of BITS (= 1, 2 or 4) for antialiasing of drawings.  Default: BITS = 4.

-g0
     Do not use antialiasing for drawings.

-h
     Use the B element for section headings.

-iRESOLUTION
     Use the RESOLUTION for rendered images.  Default: RESOLUTION = 100dpi.

-ISTEM
     Set the images' STEM NAME.  Default: STEM = grohtml-XXX (XXX is the process ID).

-jSTEM
     Place each section in a separate file called STEM-N.html (where N is a generated section number).

-l
     Do not generate the table of contents.

-n
     Generate simple fragment identifiers.

-oOFFSET
     Use vertical padding OFFSET for images.

-p
     Display the page rendering progress to stderr.

-r
     Do not use horizontal rules to separate headers and footers.

-sSIZE
     Set the base font size, to be modified using the elements BIG and SMALL.

-SLEVEL
     Generate separate files for sections at level LEVEL.

-v
     Print the version number.

-V
     Generate a validator button at the bottom.

-y
     Generate a signature of groff after the validator button, if any.

grohtml specific registers and strings
--------------------------------------

 -- Register: \n[ps4html, grohtml]
 -- String: \*[www-image-template, grohtml]
     The registers ps4html and www-image-template are defined by the pre-grohtml preprocessor.  pre-grohtml reads in the troff input, marks up the inline equations and passes the result firstly to

          troff -Tps -rps4html=1 -dwww-image-template=TEMPLATE

     and secondly to

          troff -Thtml

     or

          troff -Txhtml

     The POSTSCRIPT device is used to create all the image files (for -Thtml; if -Txhtml is used, all equations are passed to geqn to produce MathML, and the register ps4html enables the macro sets to ignore floating keeps, footers, and headings.

     The register www-image-template is set to the user specified template name or the default name.

gxditview
=========

Invoking gxditview
------------------

File formats
************

All files read and written by gtroff are text files.  The following two sections describe their format.

gtroff Output
=============

This section describes the intermediate output format of GNU troff.  This output is produced by a run of gtroff before it is fed into a device postprocessor program.

As groff is a wrapper program around gtroff that automatically calls a postprocessor, this output does not show up normally.  This is why it is called intermediate.  groff provides the option -Z to inhibit postprocessing, such that the produced intermediate output is sent to standard output just like calling gtroff manually.

Here, the term troff output describes what is output by gtroff, while intermediate output refers to the language that is accepted by the parser that prepares this output for the postprocessors.  This parser is smarter on whitespace and implements obsolete elements for compatibility, otherwise both formats are the same. (The parser and postprocessor for intermediate output can
be found in the file

GROFF-SOURCE-DIR/src/libs/libdriver/input.cpp.)

The main purpose of the intermediate output concept is to facilitate the development of postprocessors by providing a common programming interface for all devices.  It has a language of its own that is completely different from the gtroff language.  While the gtroff language is a high-level programming language for text processing, the intermediate output language is a kind of low-level assembler language by specifying all positions on the page for writing and drawing.

The intermediate output produced by gtroff is fairly readable, while output from AT&T troff is rather hard to understand because of strange habits that are still supported, but not used any longer by gtroff.

Language Concepts
-----------------

During the run of gtroff, the input data is cracked down to the information on what has to be printed at what position on the intended device.  So the language of the intermediate output format can be quite small.  Its only elements are commands with and without arguments.  In this section, the term command always refers to the intermediate output language, and never to the gtroff language used for document formatting.  There are commands for positioning and text writing, for drawing, and for device controlling.

Separation
..........

AT&T troff output has strange requirements on whitespace.  The gtroff output parser, however, is smart about whitespace by making it maximally optional.  The whitespace characters, i.e., the tab, space, and newline characters, always have a syntactical meaning.  They are never printable because spacing within the output is always done by positioning commands.

Any sequence of space or tab characters is treated as a single syntactical space.  It separates commands and arguments, but is only required when there would occur a clashing between the command code and the arguments without the space.  Most often, this happens when variable-length command names, arguments, argument lists, or command clusters meet.  Commands and arguments with a known, fixed length need not be separated by syntactical space.

A line break is a syntactical element, too.  Every command argument can be followed by whitespace, a comment, or a newline character.  Thus a syntactical line break is defined to consist of optional syntactical space that is optionally followed by a comment, and a newline character.

The normal commands, those for positioning and text, consist of a single letter taking a fixed number of arguments.  For historical reasons, the parser allows stacking of such commands on the same line, but fortunately, in gtroff's intermediate output, every command with at least one argument is followed by a line break, thus providing excellent readability.

The other commands -- those for drawing and device controlling -- have a more complicated structure; some recognize long command names, and some take a variable number of arguments.  So all D and x commands were designed to request a syntactical line break after their last argument.  Only one command, x X, has an argument that can stretch over several lines; all other commands must have all of their arguments on the same line as the command, i.e., the arguments may not be split by a line break.

Empty lines (these are lines containing only space and/or a comment), can occur everywhere.  They are just ignored.

Argument Units
..............

Some commands take integer arguments that are assumed to represent values in a measurement unit, but the letter for the corresponding scale indicator is not written with the output command arguments.  Most commands assume the scale indicator u, the basic unit of the device, some use z, the scaled point unit of the device, while others, such as the color commands, expect plain integers.

Note that single characters can have the eighth bit set, as can the names of fonts and special characters.  The names of characters and fonts can be of arbitrary length.  A character that is to be printed is always in the current font.

A string argument is always terminated by the next whitespace character (space, tab, or newline); an embedded # character is regarded as part of the argument, not as the beginning of a comment command.  An integer argument is already terminated by the next non-digit character, which then is regarded as the first character of the next argument or command.

Document Parts
..............

A correct intermediate output document consists of two parts, the prologue and the body.

The task of the prologue is to set the general device parameters using three exactly specified commands.  gtroff's prologue is guaranteed to consist of the following three lines (in that order):

     x T DEVICE
     x res N H V
     x init

with the arguments set as outlined in Device Control Commands. Note that the parser for the intermediate output format is able to swallow additional whitespace and comments as well even in the prologue.

The body is the main section for processing the document data. Syntactically, it is a sequence of any commands different from the ones used in the prologue.  Processing is terminated as soon as the first x stop command is encountered; the last line of any gtroff intermediate output always contains such a command.

Semantically, the body is page oriented.  A new page is started by a p command.  Positioning, writing, and drawing commands are always done within the current page, so they cannot occur before the first p command.  Absolute positioning (by the H and V commands) is done relative to the current page; all other positioning is done relative to the current location within this page.

Command Reference
-----------------

This section describes all intermediate output commands, both from AT&T troff as well as the gtroff extensions.

Comment Command
...............

#ANYTHING<end of line>
     A comment.  Ignore any characters from the # character up to the next newline character.

     This command is the only possibility for commenting in the intermediate output.  Each comment can be preceded by arbitrary syntactical space; every command can be terminated by a comment.

Simple Commands
...............

The commands in this subsection have a command code consisting of a single character, taking a fixed number of arguments.  Most of them are commands for positioning and text writing.  These commands are smart about whitespace.  Optionally, syntactical space can be inserted before, after, and between the command letter and its arguments.  All of these commands are stackable, i.e., they can be preceded by other simple commands or followed by arbitrary other commands on the same line.  A separating syntactical space is only necessary when two integer arguments would clash or if the preceding argument ends with a string argument.

C XXX<whitespace>
     Print a special character named XXX.  The trailing syntactical space or line break is necessary to allow glyph names of arbitrary length.  The glyph is printed at the current print position; the glyph's size is read from the font file.  The print position is not changed.

c G
     Print glyph G at the current print position; (c is actually a misnomer since it outputs a glyph.) the glyph's size is read from the font file.  The print position is not changed.

f N
     Set font to font number N (a non-negative integer).

H N
     Move right to the absolute vertical position N (a non-negative integer in basic units u relative to left edge of current page.

h N
     Move N (a non-negative integer) basic units u horizontally to the right.  The original Unix troff manual allows negative values for N also, but gtroff doesn't use this.

m COLOR-SCHEME [COMPONENT ...]
     Set the color for text (glyphs), line drawing, and the outline of graphic objects using different color schemes; the analogous command for the filling color of graphic objects is DF.  The color components are specified as integer arguments between 0 and 65536.  The number of color components and their meaning vary for the different color schemes.  These commands are generated by gtroff's escape sequence \m.  No position changing.  These commands are a gtroff extension.

     mc CYAN MAGENTA YELLOW
          Set color using the CMY color scheme, having the 3 color components CYAN, MAGENTA, and YELLOW.

     md
          Set color to the default color value (black in most cases).  No component arguments.

     mg GRAY
          Set color to the shade of gray given by the argument, an integer between 0 (black) and 65536 (white).

     mk CYAN MAGENTA YELLOW BLACK
          Set color using the CMYK color scheme, having the 4 color components CYAN, MAGENTA, YELLOW, and BLACK.

     mr RED GREEN BLUE
          Set color using the RGB color scheme, having the 3 color components RED, GREEN, and BLUE.

N N
     Print glyph with index N (a non-negative integer) of the current font.  This command is a gtroff extension.

n B A
     Inform the device about a line break, but no positioning is done by this command.  In AT&T troff, the integer arguments B and A informed about the space before and after the current line to make the intermediate output more human readable without performing any action.  In groff, they are just ignored, but they must be provided for compatibility reasons.

p N
     Begin a new page in the outprint.  The page number is set to N.  This page is completely independent of pages formerly processed even if those have the same page number.  The vertical position on the outprint is automatically set to 0.  All positioning, writing, and drawing is always done relative to a page, so a p command must be issued before any of these commands.

s N
     Set point size to N scaled points (this is unit z). AT&T troff used the unit points (p) instead. See Output Language Compatibility.

t XXX<whitespace>
t XXX DUMMY-ARG<whitespace>
     Print a word, i.e., a sequence of characters XXX representing output glyphs which names are single characters, terminated by a space character or a line break; an optional second integer argument is ignored (this allows the formatter to generate an even number of arguments).  The first glyph should be printed at the current position, the current horizontal position should then be increased by the width of the first glyph, and so on for each glyph.  The widths of the glyphs are read from the font file, scaled for the current point size, and rounded to a multiple of the horizontal resolution.  Special characters cannot be printed using this command (use the C command for special characters).  This command is a gtroff extension; it is only used for devices whose DESC file contains the tcommand keyword (see DESC File Format).

u N XXX<whitespace>
     Print word with track kerning.  This is the same as the t command except that after printing each glyph, the current horizontal position is increased by the sum of the width of that glyph and N (an integer in basic units u).  This command is a gtroff extension; it is only used for devices whose DESC file contains the tcommand keyword (see DESC File Format).

V N
     Move down to the absolute vertical position N (a non-negative integer in basic units u) relative to upper edge of current page.

v N
     Move N basic units u down (N is a non-negative integer).  The original Unix troff manual allows negative values for N also, but gtroff doesn't use this.

w
     Informs about a paddable white space to increase readability.  The spacing itself must be performed explicitly by a move command.

Graphics Commands
.................

Each graphics or drawing command in the intermediate output starts with the letter D, followed by one or two characters that specify a subcommand; this is followed by a fixed or variable number of integer arguments that are separated by a single space character.  A D command may not be followed by another command on the same line (apart from a comment), so each D command is terminated by a syntactical line break.

gtroff output follows the classical spacing rules (no space between command and subcommand, all arguments are preceded by a single space character), but the parser allows optional space between the command letters and makes the space before the first argument optional. As usual, each space can be any sequence of tab and space characters.

Some graphics commands can take a variable number of arguments.  In this case, they are integers representing a size measured in basic units u.  The arguments called H1, H2, ..., HN stand for horizontal distances where positive means right, negative left.  The arguments called V1, V2, ..., VN stand for vertical distances where positive means down, negative up.  All these distances are offsets relative to the current location.

Each graphics command directly corresponds to a similar gtroff \D escape sequence.  See Drawing Requests.

Unknown D commands are assumed to be device-specific.  Its arguments are parsed as strings; the whole information is then sent to the postprocessor.

In the following command reference, the syntax element <line
break> means a syntactical line break as defined above.

D~ H1 V1 H2 V2 ... HN VN<line break>
     Draw B-spline from current position to offset (H1,V1), then to offset (H2,V2), if given, etc. up to (HN,VN).  This command takes a variable number of argument pairs; the current position is moved to the terminal point of the drawn curve.

Da H1 V1 H2 V2<line break>
     Draw arc from current position to (H1,V1)+(H2,V2) with center at (H1,V1); then move the current position to the final point of the arc.

DC D<line break>
DC D DUMMY-ARG<line break>
     Draw a solid circle using the current fill color with diameter D (integer in basic units u) with leftmost point at the current position; then move the current position to the rightmost point of the circle.  An optional second integer argument is ignored (this allows the formatter to generate an even number of arguments).  This command is a gtroff extension.

Dc D<line break>
     Draw circle line with diameter D (integer in basic units u) with leftmost point at the current position; then move the current position to the rightmost point of the circle.

DE H V<line break>
     Draw a solid ellipse in the current fill color with a horizontal diameter of H and a vertical diameter of V (both integers in basic units u) with the leftmost point at the current position; then move to the rightmost point of the ellipse.  This command is a gtroff extension.

De H V<line break>
     Draw an outlined ellipse with a horizontal diameter of H and a vertical diameter of V (both integers in basic units u) with the leftmost point at current position; then move to the rightmost point of the ellipse.

DF COLOR-SCHEME [COMPONENT ...]<line break>
     Set fill color for solid drawing objects using different color schemes; the analogous command for setting the color of text, line graphics, and the outline of graphic objects is m.  The color components are specified as integer arguments between 0 and 65536.  The number of color components and their meaning vary for the different color schemes. These commands are generated by gtroff's escape sequences \D'F ...' and \M (with no other corresponding graphics commands).  No position changing.  This command is a gtroff extension.

     DFc CYAN MAGENTA YELLOW<line break>
          Set fill color for solid drawing objects using the CMY color scheme, having the 3 color components CYAN, MAGENTA, and YELLOW.

     DFd<line break>
          Set fill color for solid drawing objects to the default fill color value (black in most cases).  No component arguments.

     DFg GRAY<line break>
          Set fill color for solid drawing objects to the shade of gray given by the argument, an integer between 0 (black) and 65536 (white).

     DFk CYAN MAGENTA YELLOW BLACK<line break>
          Set fill color for solid drawing objects using the CMYK color scheme, having the 4 color components CYAN, MAGENTA, YELLOW, and BLACK.

     DFr RED GREEN BLUE<line break>
          Set fill color for solid drawing objects using the RGB color scheme, having the 3 color components RED, GREEN, and BLUE.

Df N<line break>
     The argument N must be an integer in the range -32767 to 32767.

     0 <= N <= 1000
          Set the color for filling solid drawing objects to a shade of gray, where 0 corresponds to solid white, 1000 (the default) to solid black, and values in between to intermediate shades of gray; this is obsoleted by command DFg.

     N < 0 or N > 1000
          Set the filling color to the color that is currently being used for the text and the outline, see command m.  For example, the command sequence

               mg 0 0 65536
               Df -1

          sets all colors to blue.

     No position changing.  This command is a gtroff extension.

Dl H V<line break>
     Draw line from current position to offset (H,V) (integers in basic units u); then set current position to the end of the drawn line.

Dp H1 V1 H2 V2 ... HN VN<line break>
     Draw a polygon line from current position to offset (H1,V1), from there to offset (H2,V2), etc. up to offset (HN,VN), and from there back to the starting position.  For historical reasons, the position is changed by adding the sum of all arguments with odd index to the actual horizontal position and the even ones to the vertical position.  Although this doesn't make sense it is kept for compatibility. This command is a gtroff extension.

DP H1 V1 H2 V2 ... HN VN<line break>
     Draw a solid polygon in the current fill color rather than an outlined polygon, using the same arguments and positioning as the corresponding Dp command. This command is a gtroff extension.

Dt N<line break>
     Set the current line thickness to N (an integer in basic units u) if N>0; if N=0 select the smallest available line thickness; if N<0 set the line thickness proportional to the point size (this is the default before the first Dt command was specified).  For historical reasons, the horizontal position is changed by adding the argument to the actual horizontal position, while the vertical position is not changed. Although this doesn't make sense it is kept for compatibility. This command is a gtroff extension.

Device Control Commands
.......................

Each device control command starts with the letter x, followed by a space character (optional or arbitrary space or tab in gtroff) and a subcommand letter or word; each argument (if any) must be preceded by a syntactical space.  All x commands are terminated by a syntactical line break; no device control command can be followed by another command on the same line (except a comment).

The subcommand is basically a single letter, but to increase readability, it can be written as a word, i.e., an arbitrary sequence of characters terminated by the next tab, space, or newline character.  All characters of the subcommand word but the first are simply ignored.  For example, gtroff outputs the initialization command x i as x init and the resolution command x r as x res.

In the following, the syntax element <line break> means a syntactical line break (see Separation).

xF NAME<line break>
     The F stands for FILENAME.

     Use NAME as the intended name for the current file in error reports.  This is useful for remembering the original file name when gtroff uses an internal piping mechanism.  The input file is not changed by this command.  This command is a gtroff extension.

xf N S<line break>
     The f stands for FONT.

     Mount font position N (a non-negative integer) with font named S (a text word).  See Font Positions.

xH N<line break>
     The H stands for HEIGHT.

     Set glyph height to N (a positive integer in scaled points z).  AT&T troff uses the unit points (p) instead.  See Output Language Compatibility.

xi<line break>
     The i stands for INIT.

     Initialize device.  This is the third command of the prologue.

xp<line break>
     The p stands for PAUSE.

     Parsed but ignored.  The original Unix troff manual writes

          pause device, can be restarted

xr N H V<line break>
     The r stands for RESOLUTION.

     Resolution is N, while H is the minimal horizontal motion, and V the minimal vertical motion possible with this device; all arguments are positive integers in basic units u per inch.  This is the second command of the prologue.

xS N<line break>
     The S stands for SLANT.

     Set slant to N (an integer in basic units u).

xs<line break>
     The s stands for STOP.

     Terminates the processing of the current file; issued as the last command of any intermediate troff output.

xt<line break>
     The t stands for TRAILER.

     Generate trailer information, if any.  In GTROFF, this is actually just ignored.

xT XXX<line break>
     The T stands for TYPESETTER.

     Set name of device to word XXX, a sequence of characters ended by the next white space character.  The possible device names coincide with those from the groff -T option.  This is the first command of the prologue.

xu N<line break>
     The u stands for UNDERLINE.

     Configure underlining of spaces.  If N is 1, start underlining of spaces; if N is 0, stop underlining of spaces. This is needed for the cu request in nroff mode and is ignored otherwise.  This command is a gtroff extension.

xX ANYTHING<line break>
     The x stands for X-ESCAPE.

     Send string ANYTHING uninterpreted to the device.  If the line following this command starts with a + character this line is interpreted as a continuation line in the following sense.  The + is ignored, but a newline character is sent instead to the device, the rest of the line is sent uninterpreted.  The same applies to all following lines until the first character of a line is not a + character.  This command is generated by the gtroff escape sequence \X.  The line-continuing feature is a gtroff extension.

Obsolete Command
................

In AT&T troff output, the writing of a single glyph is mostly done by a very strange command that combines a horizontal move and a single character giving the glyph name.  It doesn't have a command code, but is represented by a 3-character argument consisting of exactly 2 digits and a character.

DDG
     Move right DD (exactly two decimal digits) basic units u, then print glyph G (represented as a single character).

     In gtroff, arbitrary syntactical space around and within this command is allowed to be added.  Only when a preceding command on the same line ends with an argument of variable length a separating space is obligatory.  In AT&T troff, large clusters of these and other commands are used, mostly without spaces; this made such output almost unreadable.

For modern high-resolution devices, this command does not make sense because the width of the glyphs can become much larger than two decimal digits.  In gtroff, this is only used for the devices X75, X75-12, X100, and X100-12.  For other devices, the commands t and u provide a better functionality.

Intermediate Output Examples
----------------------------

This section presents the intermediate output generated from the same input for three different devices.  The input is the sentence hell world fed into gtroff on the command line.

High-resolution device ps

     This is the standard output of gtroff if no -T option is given.

          shell> echo "hell world" | groff -Z -T ps

          x T ps
          x res 72000 1 1
          x init

          p1
          x font 5 TR
          f5
          s10000
          V12000
          H72000
          thell
          wh2500
          tw
          H96620
          torld
          n12000 0

          x trailer
          V792000
          x stop

     This output can be fed into grops to get its representation as a POSTSCRIPT file.

Low-resolution device latin1

     This is similar to the high-resolution device except that the positioning is done at a minor scale.  Some comments (lines starting with #) were added for clarification; they were not generated by the formatter.

          shell> echo "hell world" | groff -Z -T latin1

          # prologue
          x T latin1
          x res 240 24 40
          x init

          # begin a new page
          p1
          # font setup
          x font 1 R
          f1
          s10
          # initial positioning on the page
          V40
          H0
          # write text `hell'
          thell
          # inform about space, and issue a horizontal jump
          wh24
          # write text `world'
          tworld
          # announce line break, but do nothing because ...
          n40 0

          # ... the end of the document has been reached
          x trailer
          V2640
          x stop

     This output can be fed into grotty to get a formatted text document.

AT&T troff output
     Since a computer monitor has a very low resolution compared to modern printers the intermediate output for the X Window devices can use the jump-and-write command with its 2-digit displacements.

          shell> echo "hell world" | groff -Z -T X100

          x T X100
          x res 100 1 1
          x init

          p1
          x font 5 TR
          f5
          s10
          V16
          H100
          # write text with jump-and-write commands
          ch07e07l03lw06w11o07r05l03dh7
          n16 0

          x trailer
          V1100
          x stop

     This output can be fed into xditview or gxditview for displaying in X.

     Due to the obsolete jump-and-write command, the text clusters in the AT&T troff output are almost unreadable.

Output Language Compatibility
-----------------------------

The intermediate output language of AT&T troff was first documented in the Unix troff manual, with later additions documented in A Typesetter-independent TROFF, written by Brian Kernighan.

The gtroff intermediate output format is compatible with this specification except for the following features.

  * The classical quasi device independence is not yet implemented.

  * The old hardware was very different from what we use today.  So the groff devices are also fundamentally different from the ones in AT&T troff.  For example, the AT&T POSTSCRIPT device is called post and has a resolution of only 720 units per inch, suitable for printers 20 years ago, while groff's ps device has a resolution of 72000 units per inch.  Maybe, by implementing some rescaling mechanism similar to the classical quasi device independence, groff could emulate AT&T's post device.

  * The B-spline command D~ is correctly handled by the intermediate output parser, but the drawing routines aren't implemented in some of the postprocessor programs.

  * The argument of the commands s and x H has the implicit unit scaled point z in gtroff, while AT&T troff has point (p).  This isn't an incompatibility but a compatible extension, for both units coincide for all devices without a sizescale parameter in the DESC file, including all postprocessors from AT&T and groff's text devices.  The few groff devices with a sizescale parameter either do not exist for AT&T troff, have a different name, or seem to have a different resolution.  So conflicts are very unlikely.

  * The position changing after the commands Dp, DP, and Dt is illogical, but as old versions of gtroff used this feature it is kept for compatibility reasons.

Font Files
==========

The gtroff font format is roughly a superset of the ditroff font format (as used in later versions of AT&T troff and its descendants).  Unlike the ditroff font format, there is no associated binary format; all files are text files. (Plan 9 troff has also abandoned the binary format.)  The font files for device NAME are stored in a directory devNAME.  There are two types of file: a device description file called DESC and for each font F a font file called F.

DESC File Format
----------------

The DESC file can contain the following types of line.  Except for the charset keyword, which must come last (if at all), the order of the lines is not important.  Later entries in the file, however, override previous values.

charset
     This line and everything following in the file are ignored.  It is allowed for the sake of backwards compatibility.

family FAM
     The default font family is FAM.

fonts N F1 F2 F3 ... FN
     Fonts F1 ... FN are mounted in the font positions M+1, ..., M+N where M is the number of styles.  This command may extend over more than one line.  A font name of 0 means no font is mounted on the corresponding font position.

hor N
     The horizontal resolution is N machine units.  All horizontal quantities are rounded to be multiples of this value.

image_generator STRING
     Needed for grohtml only.  It specifies the program to generate PNG images from POSTSCRIPT input.  Under GNU/Linux this is usually gs but under other systems (notably cygwin) it might be set to another name.

paperlength N
     The physical vertical dimension of the output medium in machine units. This isn't used by troff itself but by output devices. Deprecated.  Use papersize instead.

papersize STRING ...
     Select a paper size.  Valid values for STRING are the ISO paper types A0--A7, B0--B7, C0--C7, D0--D7, DL, and the US paper types letter, legal, tabloid, ledger, statement, executive, com10, and monarch.  Case is not significant for STRING if it holds predefined paper types. Alternatively, STRING can be a file name (e.g. /etc/papersize); if the file can be opened, groff reads the first line and tests for the above paper sizes.  Finally, STRING can be a custom paper size in the format LENGTH,WIDTH (no spaces before and after the comma). Both LENGTH and WIDTH must have a unit appended; valid values are i for inches, c for centimeters, p for points, and P for picas.  Example: 12c,235p.  An argument that starts with a digit is always treated as a custom paper format. papersize sets both the vertical and horizontal dimension of the output medium.

     More than one argument can be specified; groff scans from left to right and uses the first valid paper specification.

paperwidth N
     The physical horizontal dimension of the output medium in machine units. This isn't used by troff itself but by output devices. Deprecated.  Use papersize instead.

pass_filenames
     Tell gtroff to emit the name of the source file currently being processed.  This is achieved by the intermediate output command F.  Currently, this is only used by the grohtml output device.

postpro PROGRAM
     Call PROGRAM as a postprocessor.  For example, the line

          postpro grodvi

     in the file devdvi/DESC makes groff call grodvi if option -Tdvi is given (and -Z isn't used).

prepro PROGRAM
     Call PROGRAM as a preprocessor.  Currently, this keyword is used by groff with option -Thtml or -Txhtml only.

print PROGRAM
     Use PROGRAM as a spooler program for printing.  If omitted, the -l and -L options of groff are ignored.

res N
     There are N machine units per inch.

sizes S1 S2 ... SN 0
     This means that the device has fonts at S1, S2, ... SN scaled points.  The list of sizes must be terminated by 0 (this is digit zero).  Each SI can also be a range of sizes M--N.  The list can extend over more than one line.

sizescale N
     The scale factor for point sizes.  By default this has a value of 1.  One scaled point is equal to one point/N.  The arguments to the unitwidth and sizes commands are given in scaled points.  See Fractional Type Sizes, for more information.

styles S1 S2 ... SM
     The first M font positions are associated with styles S1 ... SM.

tcommand
     This means that the postprocessor can handle the t and u intermediate output commands.

unicode
     Indicate that the output device supports the complete Unicode repertoire.  Useful only for devices that produce character entities instead of glyphs.

     If unicode is present, no charset section is required in the font description files since the Unicode handling built into groff is used.  However, if there are entries in a charset section, they either override the default mappings for those particular characters or add new mappings (normally for composite characters).

     This is used for -Tutf8, -Thtml, and -Txhtml.

unitwidth N
     Quantities in the font files are given in machine units for fonts whose point size is N scaled points.

unscaled_charwidths
     Make the font handling module always return unscaled character widths. Needed for the grohtml device.

use_charnames_in_special
     This command indicates that gtroff should encode special characters inside special commands.  Currently, this is only used by the grohtml output device.  See Postprocessor Access.

vert N
     The vertical resolution is N machine units.  All vertical quantities are rounded to be multiples of this value.

The res, unitwidth, fonts, and sizes lines are mandatory.  Other commands are ignored by gtroff but may be used by postprocessors to store arbitrary information about the device in the DESC file.

Here a list of obsolete keywords that are recognized by groff but completely ignored: spare1, spare2, biggestfont.

Font File Format
----------------

A font file, also (and probably better) called a font description file, has two sections.  The first section is a sequence of lines each containing a sequence of blank delimited words; the first word in the line is a key, and subsequent words give a value for that key.

name F
     The name of the font is F.

spacewidth N
     The normal width of a space is N.

slant N
     The glyphs of the font have a slant of N degrees.  (Positive means forward.)

ligatures LIG1 LIG2 ... LIGN [0]
     Glyphs LIG1, LIG2, ..., LIGN are ligatures; possible ligatures are ff, fi, fl, ffi and ffl.  For backwards compatibility, the list of ligatures may be terminated with a 0.  The list of ligatures may not extend over more than one line.

special
     The font is special; this means that when a glyph is requested that is not present in the current font, it is searched for in any special fonts that are mounted.

Other commands are ignored by gtroff but may be used by postprocessors to store arbitrary information about the font in the font file.

The first section can contain comments, which start with the # character and extend to the end of a line.

The second section contains one or two subsections.  It must contain a charset subsection and it may also contain a kernpairs subsection.  These subsections can appear in any order.  Each subsection starts with a word on a line by itself.

The word charset starts the character set subsection. (This keyword is misnamed since it starts a list of ordered glyphs, not characters.)  The charset line is followed by a sequence of lines.  Each line gives information for one glyph.  A line comprises a number of fields separated by blanks or tabs.  The format is

     NAME METRICS TYPE CODE [ENTITY-NAME] [-- COMMENT]

NAME identifies the glyph name (The distinction between input, characters, and output, glyphs, is not clearly separated in the terminology of groff; for example, the char request should be called glyph since it defines an output entity.): If NAME is a single character C then it corresponds to the gtroff input character C; if it is of the form \C where C is a single character, then it corresponds to the special character \[C]; otherwise it corresponds to the special character \[NAME].  If it is exactly two characters XX it can be entered as \(XX.  Note that single-letter special characters can't be accessed as \C; the only exception is \-, which is identical to \[-].

gtroff supports 8-bit input characters; however some utilities have difficulties with eight-bit characters.  For this reason, there is a convention that the entity name charN is equivalent to the single input character whose code is N.  For example, char163 would be equivalent to the character with code 163, which is the pounds sterling sign in the ISO Latin-1 character set.  You shouldn't use charN entities in font description files since they are related to input, not output.  Otherwise, you get hard-coded connections between input and output encoding, which prevents use of different (input) character sets.

The name --- is special and indicates that the glyph is unnamed; such glyphs can only be used by means of the \N escape sequence in gtroff.

The TYPE field gives the glyph type:

1
     the glyph has a descender, for example, p;

2
     the glyph has an ascender, for example, b;

3
     the glyph has both an ascender and a descender, for example, (.

The CODE field gives the code that the postprocessor uses to print the glyph.  The glyph can also be input to gtroff using this code by means of the \N escape sequence.  CODE can be any integer.  If it starts with 0 it is interpreted as octal; if it starts with 0x or 0X it is interpreted as hexadecimal. Note, however, that the \N escape sequence only accepts a decimal integer.

The ENTITY-NAME field gives an ASCII string identifying the glyph that the postprocessor uses to print the gtroff glyph NAME.  This field is optional and has been introduced so that the grohtml device driver can encode its character set.  For example, the glyph \[Po] is represented as &pound; in HTML 4.0.

Anything on the line after the ENTITY-NAME field resp. after -- is ignored.

The METRICS field has the form:

     WIDTH[,HEIGHT[,DEPTH[,ITALIC-CORRECTION
       [,LEFT-ITALIC-CORRECTION[,SUBSCRIPT-CORRECTION]]]]]

There must not be any spaces between these subfields (it has been split here into two lines for better legibility only).  Missing subfields are assumed to be 0.  The subfields are all decimal integers.  Since there is no associated binary format, these values are not required to fit into a variable of type char as they are in ditroff. The WIDTH subfield gives the width of the glyph.  The HEIGHT subfield gives the height of the glyph (upwards is positive); if a glyph does not extend above the baseline, it should be given a zero height, rather than a negative height.  The DEPTH subfield gives the depth of the glyph, that is, the distance from the baseline to the lowest point below the baseline to which the glyph extends (downwards is positive); if a glyph does not extend below the baseline, it should be given a zero depth, rather than a negative depth.  The ITALIC-CORRECTION subfield gives the amount of space that should be added after the glyph when it is immediately to be followed by a glyph from a roman font.  The LEFT-ITALIC-CORRECTION subfield gives the amount of space that should be added before the glyph when it is immediately to be preceded by a glyph from a roman font.  The SUBSCRIPT-CORRECTION gives the amount of space that should be added after a glyph before adding a subscript.  This should be less than the italic correction.

A line in the charset section can also have the format

     NAME "

This indicates that NAME is just another name for the glyph mentioned in the preceding line.

The word kernpairs starts the kernpairs section.  This contains a sequence of lines of the form:

     C1 C2 N

This means that when glyph C1 appears next to glyph C2 the space between them should be increased by N.  Most entries in the kernpairs section have a negative value for N.

Installation
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Copying This Manual
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     [file fdl.texi not included]

Request Index
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Requests appear without the leading control character (normally either . or ').

Escape Index
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Any escape sequence \X with X not in the list below emits a warning, printing glyph X.

Register Index
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The macro package or program a specific register belongs to is appended in brackets.

A register name x consisting of exactly one character can be accessed as \nx.  A register name xx consisting of exactly two characters can be accessed as \n(xx.  Register names xxx of any length can be accessed as \n[xxx].

Macro Index
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The macro package a specific macro belongs to is appended in brackets. They appear without the leading control character (normally .).

String Index
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The macro package or program a specific string belongs to is appended in brackets.

A string name x consisting of exactly one character can be accessed as \*x.  A string name xx consisting of exactly two characters can be accessed as \*(xx.  String names xxx of any length can be accessed as \*[xxx].

Glyph Name Index
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A glyph name xx consisting of exactly two characters can be accessed as \(xx.  Glyph names xxx of any length can be accessed as \[xxx].