Ubuntu Manpage: groff - front end to the GNU roff document formatting system

Name

       groff - front end to the GNU roff document formatting system

Synopsis

       groff [-abcCeEgGijklNpRsStUVXzZ] [-d ctext] [-d string=text] [-D fallback-encoding]
             [-f font-family] [-F font-directory] [-I inclusion-directory] [-K input-encoding]
             [-L spooler-argument] [-m macro-package] [-M macro-directory] [-n page-number]
             [-o page-list] [-P postprocessor-argument] [-r cnumeric-expression]
             [-r register=numeric-expression] [-T output-device] [-w warning-category]
             [-W warning-category] [file ...]

       groff -h
       groff --help

       groff -v [option ...] [file ...]
       groff --version [option ...] [file ...]

Description

       groff is the primary front end to the GNU roff document formatting system.  GNU roff is  a
       typesetting  system  that reads plain text input files that include formatting commands to
       produce output in PostScript, PDF, HTML, DVI, or  other  formats,  or  for  display  to  a
       terminal.   Formatting  commands  can  be  low-level typesetting primitives, macros from a
       supplied package, or user-defined macros.  All three approaches can be  combined.   If  no
       file operands are specified, or if file is “-”, groff reads the standard input stream.

       A  reimplementation  and  extension  of the typesetter from AT&T Unix, groff is present on
       most POSIX systems owing to its long association with Unix manuals (including man  pages).
       It  and  its predecessor are notable for their production of several best-selling software
       engineering texts.  groff is capable of producing typographically sophisticated  documents
       while consuming minimal system resources.

       The groff command orchestrates the execution of preprocessors, the transformation of input
       documents into a device-independent page  description  language,  and  the  production  of
       output from that language.

Options

-h and --help display a usage message and exit.

Because groff is intended to subsume most users' direct invocations of the troff(1)
formatter, the two programs share a set of options. However, groff has some options that
troff does not share, and others which groff interprets differently. At the same time,
not all valid troff options can be given to groff.

groff-specific options
The following options either do not exist in GNU troff or are interpreted differently by
groff.

-D enc Set fallback input encoding used by preconv(1) to enc; implies -k.

-e Run eqn(1) preprocessor.

-g Run grn(1) preprocessor.

-G Run grap(1) preprocessor; implies -p.

-I dir Works as troff's option (see below), but also implies -g and -s. It is passed to
soelim(1) and the output driver, and grn is passed an -M option with dir as its
argument.

-j Run chem(1) preprocessor; implies -p.

-k Run preconv(1) preprocessor. Refer to its man page for its behavior if neither of
groff's -K or -D options is also specified.

-K enc Set input encoding used by preconv(1) to enc; implies -k.

-l Send the output to a spooler program for printing. The “print” directive in the
device description file specifies the default command to be used; see
groff_font(5). If no such directive is present for the output device, output is
piped to lpr(1). See options -L and -X.

-L arg Pass arg to the print spooler program. If multiple args are required, pass each
with a separate -L option. groff does not prefix an option dash to arg before
passing it to the spooler program.

-M Works as troff's option (see below), but is also passed to eqn(1), grap(1), and
grn(1).

-N Prohibit newlines between eqn delimiters: pass -N to eqn(1).

-p Run pic(1) preprocessor.

-P arg Pass arg to the postprocessor. If multiple args are required, pass each with a
separate -P option. groff does not prefix an option dash to arg before passing it
to the postprocessor.

-R Run refer(1) preprocessor. No mechanism is provided for passing arguments to refer
because most refer options have equivalent language elements that can be specified
within the document.

-s Run soelim(1) preprocessor.

-S Operate in “safer” mode; see -U below for its opposite. For security reasons,
safer mode is enabled by default.

-t Run tbl(1) preprocessor.

-T dev Direct troff to format the input for the output device dev. groff then calls an
output driver to convert troff's output to a form appropriate for dev; see
subsection “Output devices” below.

-U Operate in unsafe mode: pass the -U option to pic and troff.

-v
--version
Write version information for groff and all programs run by it to the standard
output stream; that is, the given command line is processed in the usual way,
passing -v to the formatter and any pre- or postprocessors invoked.

-V Output the pipeline that groff would run to the standard output stream, but do not
execute it. If given more than once, groff both writes and runs the pipeline.

-X Use gxditview(1) instead of the usual postprocessor to (pre)view a document on an
X11 display. Combining this option with -Tps uses the font metrics of the
PostScript device, whereas the -TX75 and -TX100 options use the metrics of X11
fonts.

-Z Disable postprocessing. troff output will appear on the standard output stream
(unless suppressed with -z); see groff_out(5) for a description of this format.

Transparent options
The following options are passed as-is to the formatter program troff(1) and described in
more detail in its man page.

-a Generate a plain text approximation of the typeset output.

-b Write a backtrace to the standard error stream on each error or warning.

-c Start with color output disabled.

-C Enable AT&T troff compatibility mode; implies -c.

-d cs
-d name=string
Define string.

-E Inhibit troff error messages; implies -Ww.

-f fam Set default font family.

-F dir Search in directory dir for the selected output device's directory of device and
font description files.

-i Process standard input after the specified input files.

-I dir Search dir for input files.

-m name
Process name.tmac before input files.

-M dir Search directory dir for macro files.

-n num Number the first page num.

-o list
Output only pages in list.

-r cnumeric-expression
-r register=numeric-expression
Define register.

-w name
-W name
Enable (-w) or inhibit (-W) emission of warnings in category name.

-z Suppress formatted device-independent output of troff.

Usage

The architecture of the GNU roff system follows that of other device-independent roff
implementations, comprising preprocessors, macro packages, output drivers (or
“postprocessors”), a suite of utilities, and the formatter troff at its heart. See
roff(7) for a survey of how a roff system works.

The front end programs available in the GNU roff system make it easier to use than
traditional roffs that required the construction of pipelines or use of temporary files to
carry a source document from maintainable form to device-ready output. The discussion
below summarizes the constituent parts of the GNU roff system. It complements roff(7)
with groff-specific information.

Getting started
Those who prefer to learn by experimenting or are desirous of rapid feedback from the
system may wish to start with a “Hello, world!” document.

$ echo "Hello, world!" | groff -Tascii | sed '/^$/d'
Hello, world!

We used a sed command only to eliminate the 65 blank lines that would otherwise flood the
terminal screen. (roff systems were developed in the days of paper-based terminals with
66 lines to a page.)

Today's users may prefer output to a UTF-8-capable terminal.

$ echo "Hello, world!" | groff -Tutf8 | sed '/^$/d'

Producing PDF, HTML, or TeX's DVI is also straightforward. The hard part may be selecting
a viewer program for the output.

$ echo "Hello, world!" | groff -Tpdf > hello.pdf
$ evince hello.pdf
$ echo "Hello, world!" | groff -Thtml > hello.html
$ firefox hello.html
$ echo "Hello, world!" | groff -Tdvi > hello.dvi
$ xdvi hello.html

Using groff as a REPL
Those with a programmer's bent may be pleased to know that they can use groff in a read-
evaluate-print loop (REPL). Doing so can be handy to verify one's understanding of the
formatter's behavior and/or the syntax it accepts. Turning on all warnings with -ww can
aid this goal.

$ groff -ww -Tutf8
\# This is a comment. Let's define a register.
.nr a 1
\# Do integer arithmetic with operators evaluated left-to-right.
.nr b \n[a]+5/2
\# Let's get the result on the standard error stream.
.tm \n[b]
3
\# Now we'll define a string.
.ds name Leslie\" This is another form of comment.
.nr b (\n[a] + (7/2))
\# Center the next two text input lines.
.ce 2
Hi, \*[name].
Your secret number is \n[b].
\# We will see that the division rounded toward zero.
It is
\# Here's an if-else control structure.
.ie (\n[b] % 2) odd.
.el even.
\# This trick sets the page length to the current vertical
\# position, so that blank lines don't spew when we're done.
.pl \n[nl]u
<Control-D>
Hi, Leslie.
Your secret number is 4.
It is even.

Paper format
In GNU roff, the page dimensions for the formatter troff and for output devices are
handled separately. In the formatter, requests are used to set the page length (.pl),
page offset (or left margin, .po), and line length (.ll). The right margin is not
explicitly configured; the combination of page offset and line length provides the
information necessary to derive it. The papersize macro package, automatically loaded by
troff, provides an interface for configuring page dimensions by convenient names, like
“letter” or “A4”; see groff_tmac(5). The formatter's default in this installation is “‐
A4”.

It is up to each macro package to respect the page dimensions configured in this way.
Some offer alternative mechanisms.

For each output device, the size of the output medium can be set in its DESC file. Most
output drivers also recognize a command-line option -p to override the default dimensions
and an option -l to use landscape orientation. See groff_font(5) for a description of the
papersize directive, which takes an argument of the same form as -p. The output driver's
man page, such as grops(1), may also be helpful. groff uses the command-line option -P to
pass options to output devices; for example, use the following for PostScript output on A4
paper in landscape orientation.

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

Front end
The groff program is a wrapper around the troff(1) program. It allows one to specify
preprocessors via command-line options and automatically runs the appropriate
postprocessor for the selected output device. Doing so, the manual construction of
pipelines or management of temporary files required of users of traditional roff(7)
systems can be avoided. Use the grog(1) program to infer an appropriate groff command
line to format a document.

Language
Input to a roff system is in plain text interleaved with control lines and escape
sequences. The combination constitutes a document in one of a family of languages we also
call roff; see roff(7) for background. An overview of GNU roff language syntax and
features, including lists of all supported escape sequences, requests, and predefined
registers, can be found in groff(7). GNU roff extensions to the AT&T troff language, a
common subset of roff dialects extant today, are detailed in groff_diff(7).

Preprocessors
A preprocessor interprets a domain-specific language that produces roff language output.
Frequently, such input is confined to sections or regions of a roff input file (bracketed
with macro calls specific to each preprocessor), which it replaces. Preprocessors
therefore often interpret a subset of roff syntax along with their own language. GNU roff
provides reimplementations of most preprocessors familiar to users of AT&T troff; these
routinely have extended features and/or require GNU troff to format their output.

tbl lays out tables;
eqn typesets mathematics;
pic draws diagrams;
refer processes bibliographic references;
soelim preprocesses “sourced” input files;
grn renders gremlin(1) diagrams;
chem draws chemical structural formulæ using pic;
gperl populates groff registers and strings using perl(1);
glilypond embeds LilyPond sheet music; and
gpinyin eases Mandarin Chinese input using Hanyu Pinyin.

A preprocessor unique to GNU roff is preconv(1), which converts various input encodings to
something GNU troff can understand. When used, it is run before any other preprocessors.

Most preprocessors enclose content between a pair of characteristic tokens. Such a token
must occur at the beginning of an input line and use the dot control character. Spaces
and tabs must not follow the control character or precede the end of the input line.
Deviating from these rules defeats a token's recognition by the preprocessor. Tokens are
generally preserved in preprocessor output and interpreted as macro calls subsequently by
troff. The ideal preprocessor is not yet available in groff.

┌─────────────┬─────────────────┬────────────────┐
│preprocessor │ starting token │ ending token │
├─────────────┼─────────────────┼────────────────┤
│ chem │ .cstart │ .cend │
│ eqn │ .EQ │ .EN │
│ grap │ .G1 │ .G2 │
│ grn │ .GS │ .GE │
│ ideal │ .IS │ .IE │
│ │ │ .IF │
│ pic │ .PS │ .PE │
│ │ │ .PF │
│ │ │ .PY │
│ refer │ .R1 │ .R2 │
│ tbl │ .TS │ .TE │
├─────────────┼─────────────────┼────────────────┤
│ glilypond │ .lilypond start │ .lilypond stop │
│ gperl │ .Perl start │ .Perl stop │
│ gpinyin │ .pinyin start │ .pinyin stop │
└─────────────┴─────────────────┴────────────────┘
Macro packages
Macro files are roff input files designed to produce no output themselves but instead ease
the preparation of other roff documents. When a macro file is installed at a standard
location and suitable for use by a general audience, it is termed a macro package.

Macro packages can be loaded prior to any roff input documents with the -m option. The
GNU roff system implements most well-known macro packages for AT&T troff in a compatible
way and extends them. These have one- or two-letter names arising from intense practices
of naming economy in early Unix culture, a laconic approach that led to many of the
packages being identified in general usage with the nroff and troff option letter used to
invoke them, sometimes to punning effect, as with “man” (short for “manual”), and even
with the option dash, as in the case of the s package, much better known as ms or even
-ms.

Macro packages serve a variety of purposes. Some are “full-service” packages, adopting
responsibility for page layout among other fundamental tasks, and defining their own
lexicon of macros for document composition; each such package stands alone and a given
document can use at most one.

an is used to compose man pages in the format originating in Version 7 Unix (1979);
see groff_man(7). It can be specified on the command line as -man.

doc is used to compose man pages in the format originating in 4.3BSD-Reno (1990); see
groff_mdoc(7). It can be specified on the command line as -mdoc.

e is the Berkeley general-purpose macro suite, developed as an alternative to AT&T's
s; see groff_me(7). It can be specified on the command line as -me.

m implements the format used by the second-generation AT&T macro suite for general
documents, a successor to s; see groff_mm(7). It can be specified on the command
line as -mm.

om (invariably called “mom”) is a modern package written by Peter Schaffter
specifically for GNU roff. Consult the mom HTML manual ⟨file:///usr/share/doc/
groff-base/html/mom/toc.html⟩ for extensive documentation. She—for mom takes the
female pronoun—can be specified on the command line as -mom.

s is the original AT&T general-purpose document format; see groff_ms(7). It can be
specified on the command line as -ms.

Others are supplemental. For instance, andoc is a wrapper package specific to GNU roff
that recognizes whether a document uses man or mdoc format and loads the corresponding
macro package. It can be specified on the command line as -mandoc. A man(1) librarian
program may use this macro file to delegate loading of the correct macro package; it is
thus unnecessary for man itself to scan the contents of a document to decide the issue.

Many macro files augment the function of the full-service packages, or of roff documents
that do not employ such a package—the latter are sometimes characterized as “raw”. These
auxiliary packages are described, along with details of macro file naming and placement,
in groff_tmac(5).

Formatters
The formatter, the program that interprets roff language input, is troff(1). It provides
the features of the AT&T troff and nroff programs as well as many extensions. The
command-line option -C switches troff into compatibility mode, which tries to emulate AT&T
troff as closely as is practical to enable the formatting of documents written for the
older system.

A shell script, nroff(1), emulates the behavior of AT&T nroff. It attempts to correctly
encode the output based on the locale, relieving the user of the need to specify an output
device with the -T option and is therefore convenient for use with terminal output
devices, described in the next subsection.

GNU troff generates output in a device-independent, but not device-agnostic, page
description language detailed in groff_out(5).

Output devices
troff output is formatted for a particular output device, typically specified by the -T
option to the formatter or a front end. If neither this option nor the GROFF_TYPESETTER
environment variable is used, the default output device is ps. An output device may be
any of the following.

ascii for terminals using the ISO 646 1991:IRV character set and encoding, also known
as US-ASCII.

cp1047 for terminals using the IBM code page 1047 character set and encoding.

dvi for TeX DVI format.

html
xhtml for HTML and XHTML output, respectively.

latin1 for terminals using the ISO Latin-1 (ISO 8859-1) character set and encoding.

lbp for Canon CaPSL printers (LBP-4 and LBP-8 series laser printers).

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

pdf for PDF output.

ps for PostScript output.

utf8 for terminals using the ISO 10646 (“Unicode”) character set in UTF-8 encoding.

X75 for previewing with gxditview using 75 dpi resolution and a 10-point base type
size.

X75-12 for previewing with gxditview using 75 dpi resolution and a 12-point base type
size.

X100 for previewing with gxditview using 100 dpi resolution and a 10-point base type
size.

X100-12 for previewing with gxditview using 100 dpi resolution and a 12-point base type
size.

Postprocessors
Any program that interprets the output of GNU troff is a postprocessor. The
postprocessors provided by GNU roff are output drivers, which prepare a document for
viewing or printing. Postprocessors for other purposes, such as page resequencing or
statistical measurement of a document, are conceivable.

An output driver supports one or more output devices, each with its own device description
file. A device determines its postprocessor with the postpro directive in its device
description file; see groff_font(5). The -X option overrides this selection, causing
gxditview to serve as the output driver.

grodvi(1)
provides dvi.

grohtml(1)
provides html and xhtml.

grolbp(1)
provides lbp.

grolj4(1)
provides lj4.

gropdf(1)
provides pdf.

grops(1)
provides ps.

grotty(1)
provides ascii, cp1047, latin1, and utf8.

gxditview(1)
provides X75, X75-12, X100, and X100-12, and additionally can preview ps.

Utilities
GNU roff includes a suite of utilities.

gdiffmk(1)
marks differences between a pair of roff input files.

grog(1)
infers the groff command a document requires.

Several utilities prepare descriptions of fonts, enabling the formatter to use them when
producing output for a given device.

addftinfo(1)
adds information to AT&T troff font description files to enable their use with GNU
troff.

afmtodit(1)
creates font description files for PostScript Type 1 fonts.

pfbtops(1)
translates a PostScript Type 1 font in PFB (Printer Font Binary) format to PFA
(Printer Font ASCII), which can then be interpreted by afmtodit.

hpftodit(1)
creates font description files for the HP LaserJet 4 family of printers.

tfmtodit(1)
creates font description files for the TeX DVI device.

xtotroff(1)
creates font description files for X Window System core fonts.

A trio of tools transform material constructed using roff preprocessor languages into
graphical image files.

eqn2graph(1)
converts an eqn equation into a cropped image.

grap2graph(1)
converts a grap diagram into a cropped image.

pic2graph(1)
converts a pic diagram into a cropped image.

Another set of programs works with the bibliographic data files used by the refer(1)
preprocessor.

indxbib(1)
makes inverted indices for bibliographic databases, speeding lookup operations on
them.

lkbib(1)
searches the databases.

lookbib(1)
interactively searches the databases.

Exit status

       groff  exits  with  a  failure  status  if there was a problem parsing its arguments and a
       successful status if either of the options -h or --help was specified.   Otherwise,  groff
       runs  a  pipeline  to  process  its  input;  if  all  commands  within  the  pipeline exit
       successfully, groff does likewise.  If not, groff's  exit  status  encodes  a  summary  of
       problems  encountered, setting bit 0 if a command exited with a failure status, bit 1 if a
       command was terminated with a signal, and bit 2  if  a  command  could  not  be  executed.
       (Thus,  if all three misfortunes befell one's pipeline, groff would exit with status 2^0 +
       2^1 + 2^2 = 1+2+4 = 7.)  To troubleshoot pipeline problems, you may  wish  to  re-run  the
       groff  command  with  the  -V  option  and  break the reported pipeline down into separate
       stages, inspecting the exit status of and diagnostic messages emitted by each command.

Environment

Normally, the path separator in environment variables ending with PATH is the colon; this
may vary depending on the operating system. For example, Windows uses a semicolon
instead.

GROFF_BIN_PATH
This search path, followed by PATH, is used to locate commands executed by groff.
If it is not set, the installation directory of the GNU roff executables, /usr/bin,
is searched before PATH.

GROFF_COMMAND_PREFIX
GNU roff can be configured at compile time to apply a prefix to the names of the
programs it provides that had a counterpart in AT&T troff, so that name collisions
are avoided at run time. The default prefix is empty.

When used, this prefix is conventionally the letter “g”. For example, GNU troff
would be installed as gtroff. Besides troff, the prefix applies to the formatter
nroff; the preprocessors eqn, grn, pic, refer, tbl, and soelim; and the utilities
indxbib and lookbib.

GROFF_ENCODING
The value of this variable is passed to the preconv(1) preprocessor's -e option to
select the character encoding of input files. This variable's existence implies
the groff option -k. If set but empty, groff calls preconv without an -e option.
groff's -K option overrides GROFF_ENCODING.

GROFF_FONT_PATH
Seek the selected output device's directory of device and font description files in
this list of directories. See troff(1) and groff_font(5).

GROFF_TMAC_PATH
Seek macro files in this list of directories. See troff(1) and groff_tmac(5).

GROFF_TMPDIR
Create temporary files in this directory. If not set, but the environment variable
TMPDIR is set, temporary files are created there instead. On Windows systems, if
neither of the foregoing are set, the environment variables TMP and TEMP (in that
order) are checked also. Otherwise, temporary files are created in /tmp. The
refer(1), grohtml(1), and grops(1) commands use temporary files.

GROFF_TYPESETTER
Set the default output device. If empty or not set, ps is used. The -T option
overrides GROFF_TYPESETTER.

SOURCE_DATE_EPOCH
A time stamp (expressed as seconds since the Unix epoch) to use as the output
creation time stamp in place of the current time. The time is converted to human-
readable form using gmtime(3) and asctime(3) when the formatter starts up and
stored in registers usable by documents and macro packages.

TZ The time zone to use when converting the current time to human-readable form; see
tzset(3). If SOURCE_DATE_EPOCH is used, it is always converted to human-readable
form using UTC.

Examples

roff systems are best known for formatting man pages. Once a man(1) librarian program has
located a man page, it may execute a groff command much like the following.
groff -t -man -Tutf8 /usr/share/man/man1/groff.1
The librarian will also pipe the output through a pager, which might not interpret the SGR
terminal escape sequences groff emits for boldface, underlining, or italics; see section
“Limitations” below.

To process a roff input file using the preprocessors tbl and pic and the me macro package
in the way to which AT&T troff users were accustomed, one would type (or script) a
pipeline.

pic foo.me | tbl | troff -me -Tutf8 | grotty

Using groff, this pipe can be shortened to an equivalent command.

groff -p -t -me -T utf8 foo.me

An even easier way to do this is to use grog(1) to guess the preprocessor and macro
options and execute the result by using the command substitution feature of the shell.

$(grog -Tutf8 foo.me)

Each command-line option to a postprocessor must be specified with any required leading
dashes “-” because groff passes the arguments as-is to the postprocessor; this permits
arbitrary arguments to be transmitted. For example, to pass a title to the gxditview
postprocessor, the shell commands
groff -X -P -title -P 'trial run' mydoc.t
and
groff -X -Z mydoc.t | gxditview -title 'trial run' -
are equivalent.

Limitations

       When paging output for the ascii, cp1047, latin1, and utf8 devices, programs like  more(1)
       and  less(1)  may  require  command-line  options to correctly handle some terminal escape
       sequences; see grotty(1).

       On EBCDIC hosts such as OS/390 Unix, the output devices ascii and latin1 aren't available.
       Conversely,  the  output device cp1047 is not available on systems based on the ISO 646 or
       ISO 8859 character encoding standards.

Installation directories

GNU roff installs files in varying locations depending on its compile-time configuration.
On this installation, the following locations are used.

/etc/X11/app-defaults
Application defaults directory for gxditview(1).

/usr/bin
Directory containing groff's executable commands.

/usr/share/groff/1.23.0/eign
List of common words for indxbib(1).

/usr/share/groff/1.23.0
Directory for data files.

/usr/dict/papers/Ind
Default index for lkbib(1) and refer(1).

/usr/share/doc/groff-base
Documentation directory.

/usr/share/doc/groff-base/examples
Example directory.

/usr/share/groff/1.23.0/font
Font directory.

/usr/share/doc/groff-base/html
HTML documentation directory.

/usr/lib/font
Legacy font directory.

/usr/share/groff/site-font
Local font directory.

/usr/share/groff/site-tmac
Local macro package (tmac file) directory.

/usr/share/groff/1.23.0/tmac
Macro package (tmac file) directory.

/usr/share/groff/1.23.0/oldfont
Font directory for compatibility with old versions of groff; see grops(1).

/usr/share/doc/groff-base/pdf
PDF documentation directory.

groff macro directory
Most macro files supplied with GNU roff are stored in /usr/share/groff/1.23.0/tmac for the
installation corresponding to this document. As a rule, multiple directories are searched
for macro files; see troff(1). For a catalog of macro files GNU roff provides, see
groff_tmac(5).

groff device and font description directory
Device and font description files supplied with GNU roff are stored in /usr/share/groff/
1.23.0/font for the installation corresponding to this document. As a rule, multiple
directories are searched for device and font description files; see troff(1). For the
formats of these files, see groff_font(5).

Availability

       Obtain  links  to  groff  releases for download, its source repository, discussion mailing
       lists, a support ticket tracker, and further information from the groff page  of  the  GNU
       website ⟨http://www.gnu.org/software/groff⟩.

       A free implementation of the grap preprocessor, written by Ted Faber ⟨faber@lunabase.org⟩,
       can be found at the  grap  website  ⟨http://www.lunabase.org/~faber/Vault/software/grap/⟩.
       groff supports only this grap.

Authors

       groff  (both  the front-end command and the overall system) was primarily written by James
       Clark ⟨jjc@jclark.com⟩.  Contributors to this document include  Clark,  Trent  A.  Fisher,
       Werner  Lemberg  ⟨wl@gnu.org⟩, Bernd Warken ⟨groff-bernd.warken-72@web.de⟩, and G. Branden
       Robinson ⟨g.branden.robinson@gmail.com⟩.