.TH groff_tmac 5 "16 October 2023" "groff 1.23.0"
.SH Name
groff_tmac \- macro files in the GNU
.I roff
typesetting system
.
.
.\" ====================================================================
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.\"
.\" This file is part of groff, the GNU roff typesetting system.
.\"
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.\" document under the terms of the GNU Free Documentation License,
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.\" and with no Back-Cover Texts.
.\"
.\" A copy of the Free Documentation License is included as a file
.\" called FDL in the main directory of the groff source package.
.\"
.\" A copy of the GNU Free Documentation License is also available in this
.\" Debian package as /usr/share/doc/groff/copyright.
.
.
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.if  \n(.g .if !d MR .nr do-fallback 1 \" older groff
.if !\n(.g           .nr do-fallback 1 \" non-groff *roff
.if \n[do-fallback]  \{\
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.\" TODO: Consider parallelizing with our Texinfo node "Macro Packages".
.\" ====================================================================
.SH Description
.\" ====================================================================
.
Definitions of macros,
strings,
and registers for use in a
.MR roff 7
document can be collected into
.IR "macro files" ,
.I roff
input files designed to produce no output themselves but instead ease
the preparation of other
.I roff
documents.
.
There is no syntactical difference between a macro file and any other
.I roff
document;
only its purpose distinguishes it.
.
When a macro file is installed at a standard location,
named according to a certain convention,
and suitable for use by a general audience,
it is termed a
.IR "macro package" .
.
Macro packages can be loaded by supplying the
.B \-m
option to
.MR \%troff 1
or a
.I groff
front end.
.
.
.P
Each macro package stores its macro,
string,
and register definitions in one or more
.I tmac
files.
.
This name originated in early Unix culture as an abbreviation of
.RI \[lq] troff \" generic
macros\[rq].
.
.
.P
A macro file must have a name in the form
.RI name .tmac
(or
.IR tmac. name)
and be placed in a
.RI \[lq] tmac
directory\[rq] to be loadable with the
.BI \-m name
option.
.
Section \[lq]Environment\[rq] of
.MR \%troff 1
lists these directories.
.
Alternatively,
a
.I groff
document requiring a macro file can load it with the
.B mso
(\[lq]macro source\[rq]) request.
.
.
.P
Like any other
.I roff
document,
a macro file can use the
.RB \[lq] so \[rq]
request (\[lq]source\[rq]) to load further files relative to its own
location.
.
.
.P
Macro files are named for their most noteworthy application,
but a macro file need not define any macros.
.
It can restrict itself to defining registers and strings or invoking
other
.I groff
requests.
.
It can even be empty.
.
.
.\" ====================================================================
.SH "Macro packages"
.\" ====================================================================
.
Macro packages come in two varieties;
those which assume responsibility for page layout and other critical
functions
(\[lq]major\[rq] or \[lq]full-service\[rq])
and those which do not
(\[lq]supplemental\[rq] or \[lq]auxiliary\[rq]).
.
GNU
.I roff
provides most major macro packages found in AT&T and BSD Unix systems,
an additional full-service package,
and many supplemental packages.
.
Multiple full-service macro packages cannot be used by the same
document.
.
Auxiliary packages can generally be freely combined,
though attention to their use of the
.I groff
language name spaces for identifiers
(particularly registers,
macros,
strings,
and diversions)
should be paid.
.
Name space management was a significant challenge in AT&T
.IR troff ;
.IR groff 's
support for arbitrarily long identifiers affords few excuses for name
collisions,
apart from attempts at compatibility with the demands of historical
documents.
.
.
.\" ====================================================================
.SS "Man pages"
.\" ====================================================================
.
.TP
.I an
.TQ
.I man
.I an
is used to compose man pages in the format originating in Version\~7
Unix (1979).
.
It has a small macro interface and is widely used;
see
.MR groff_man 7 .
.
.
.TP
.I doc
.TQ
.I mdoc
.I doc
is used to compose man pages in the format originating in 4.3BSD-Reno
(1990).
.
It provides many more features than
.IR an ,
but is also larger,
more complex,
and not as widely adopted;
see
.MR groff_mdoc 7 .
.
.
.P
Because readers of man pages often do not know in advance which macros
are used to format a given document,
a wrapper is available.
.
.
.TP
.I \%andoc
.TQ
.I mandoc
This macro file,
specific to
.IR groff ,
recognizes whether a document uses
.I man
or
.I mdoc
format and loads the corresponding macro package.
.
Multiple man pages,
in either format,
can be handled;
.I \%andoc
reloads each macro package as necessary.
.
.
.\" ====================================================================
.SS "Full-service packages"
.\" ====================================================================
.
The packages in this section provide a complete set of macros for
writing documents of any kind, up to whole books.
.
They are similar in functionality; it is a matter of taste which one
to use.
.
.
.TP
.I me
The classical
.I me
macro package; see
.MR groff_me 7 .
.
.
.TP
.I mm
The semi-classical
.I mm
macro package; see
.MR groff_mm 7 .
.
.
.TP
.I mom
The
.I mom
macro package, only available in groff.
.
As this was not based on other packages, it was freely designed as
quite a nice, modern macro package.
.
See
.MR groff_mom 7 .
.
.
.TP
.I ms
The classical
.I ms
macro package; see
.MR groff_ms 7 .
.
.
.\" ====================================================================
.SS "Localization packages"
.\" ====================================================================
.
For Western languages,
the localization file sets the hyphenation mode and loads hyphenation
patterns and exceptions.
.
Localization files can also adjust the date format and provide
translations of strings used by some of the full-service macro packages;
alter the input encoding
(see the next section);
and change the amount of additional inter-sentence space.
.
For Eastern languages,
the localization file defines character classes and sets flags on them.
.
By default,
.I troffrc
loads the localization file for English.
.
.
.TP
.I trans
loads localized strings used by various macro packages after their
localized forms have been prepared by a localization macro file.
.
.
.P
.I groff
provides the following localization files.
.
.
.TP
.I cs
Czech;
localizes
.IR man ,
.IR me ,
.IR mm ,
.IR mom ,
and
.IR ms .
.
Sets the input encoding to Latin-2 by loading
.IR latin2.tmac .
.
.
.TP
.I de
.TQ
.I den
German;
localizes
.IR man ,
.IR me ,
.IR mm ,
.IR mom ,
and
.IR ms .
.
Sets the input encoding to Latin-1 by loading
.IR latin1.tmac .
.
.
.IP
.I de.tmac
selects hyphenation patterns for traditional orthography,
and
.I den.tmac
does the same for the new orthography
(\[lq]Recht\%schreib\%reform\[rq]).
.
.
.TP
.I en
English.
.
.
.TP
.I fr
French;
localizes
.IR man ,
.IR me ,
.IR mm ,
.IR mom ,
and
.IR ms .
.
Sets the input encoding to Latin-9 by loading
.IR latin9.tmac .
.
.
.TP
.I it
Italian;
localizes
.IR man ,
.IR me ,
.IR mm ,
.IR mom ,
and
.IR ms .
.
.
.TP
.I ja
Japanese.
.
.
.TP
.I sv
Swedish;
localizes
.IR man ,
.IR me ,
.IR mm ,
.IR mom ,
and
.IR ms .
.
Sets the input encoding to Latin-1 by loading
.IR latin1.tmac .
.
Some of the localization of the
.I mm
package is handled separately;
see
.MR groff_mmse 7
(only in Swedish locales).
.
.
.TP
.I zh
Chinese.
.
.
.\" ====================================================================
.SS "Input encodings"
.\" ====================================================================
.
.TP
.I latin1
.TQ
.I latin2
.TQ
.I latin5
.TQ
.I latin9
are various ISO\~8859 input encodings supported by
.IR groff .
.
On systems using ISO character encodings,
.I groff
loads
.I latin1.tmac
automatically at startup.
.
A document that uses Latin-2,
Latin-5,
or Latin-9
can specify one of these alternative encodings.
.
.
.TP
.I cp1047
provides support for EBCDIC-based systems.
.
On those platforms,
.I groff
loads
.I cp1047.tmac
automatically at startup.
.
.
.P
Because different input character codes constitute valid GNU
.I troff \" GNU
input on ISO and EBCDIC systems,
the
.I latin
macro files cannot be used on EBCDIC systems,
and
.I cp1047
cannot be used on ISO systems.
.
.
.\" ====================================================================
.SS "Auxiliary packages"
.\" ====================================================================
.
The macro packages in this section are not intended for stand-alone
use,
but can add functionality to any other macro package or to plain
(\[lq]raw\[rq])
.I groff
documents.
.
.
.\" TODO:
.\"   a4
.\"   devtag
.\"   doc-old
.\"   europs
.\"   psatk
.\"   psfig
.TP
.I 62bit
provides macros for addition,
multiplication,
and division of 62-bit integers
(allowing safe multiplication of signed 31-bit integers,
for example).
.
.
.TP
.I hdtbl
allows the generation of tables using a syntax similar to the HTML table
model.
.
This Heidelberger table macro package is not a preprocessor,
which can be useful if the contents of table entries are determined by
macro calls or string interpolations.
.
Compare to
.MR \%tbl 1 .
.
It works only with the
.B ps
and
.B pdf
output devices.
.
See
.MR groff_hdtbl 7 .
.
.
.TP
.I papersize
enables the paper format to be set on the command line by giving a
.RB \[lq] \-d
.BI \%paper= format\c
\[rq]
option to
.IR \%troff .
.
Possible values for
.I format
are the ISO and DIN formats
.RB \[lq] A0 \[en] A6 \[rq],
.RB \[lq] B0 \[en] B6 \[rq],
.RB \[lq] C0 \[en] C6 \[rq],
and
.RB \[lq] D0 \[en] D6 \[rq];
.\" XXX: src/libs/libgroff/paper.cpp also supports [ABCD]7.
the U.S.\& formats
.RB \%\[lq] letter \[rq],
.RB \%\[lq] legal \[rq],
.RB \%\[lq] tabloid \[rq],
.RB \%\[lq] ledger \[rq],
.RB \%\[lq] statement \[rq],
and
.RB \%\[lq] executive \[rq];
and the envelope formats
.RB \%\[lq] com10 \[rq],
.RB \%\[lq] monarch \[rq],
and
.RB \%\[lq] DL \[rq].
.
All formats,
even those for envelopes,
are in portrait orientation:
the length measurement is vertical.
.
Appending \[lq]l\[rq] (ell) to any of these denotes landscape
orientation instead.
.
This macro file assumes one-inch horizontal margins,
and sets registers recognized by the
.I groff
.IR man ,
.IR mdoc ,
.IR mm ,
.IR mom ,
and
.I ms
packages to configure them accordingly.
.
If you want different margins,
you will need to use those packages' facilities,
or
.I \%troff
.B ll
and/or
.B po
requests to adjust them.
.
An output device typically requires command-line options
.B \-p
and
.B \-l
to override the paper dimensions and orientation,
respectively,
defined in its
.I DESC
file;
see subsection \[lq]Paper format\[rq]
of
.MR groff 1 .
.
This macro file is normally loaded at startup by the
.I troffrc
file when formatting for a typesetting device
(but not a terminal).
.
.
.TP
.I pdfpic
provides a single macro,
.BR PDFPIC ,
to include a PDF graphic in a document using features of the
.B pdf
output driver.
.
For other output devices,
.B PDFPIC
calls
.BR PSPIC ,
with which it shares an interface
(see below).
.
This macro file is normally loaded at startup by the
.I troffrc
file.
.
.
.TP
.I pic
supplies definitions of the macros
.BR PS ,
.BR PE ,
and
.BR PF ,
usable with the
.MR \%pic 1
preprocessor.
.
They center each picture.
.
Use it if your document does not use a full-service macro package,
or that package does not supply working
.I pic
macro definitions.
.
Except for
.I man
and
.IR mdoc ,
those provided with
.I groff
already do so
(exception:
.I mm
employs the name
.B PF
for a different purpose).
.
.
.TP
.I pspic
provides a macro,
.BR PSPIC ,
that includes a PostScript graphic in a document.
.
The
.BR ps ,
.BR dvi ,
.BR html ,
and
.B xhtml
output devices support such inclusions;
for all other drivers,
the image is replaced with a rectangular border of the same size.
.
.I pspic.tmac
is loaded at startup by the
.I troffrc
file.
.
.
.IP
Its syntax is as follows.
.RS
.IP
\&\fB.PSPIC\fP \
[\fB\-L\fP\|\
|\|\fB\-R\fP\|\
|\|\fB\-C\fP\|\
|\|\fB\-I\fP\~\fIn\fP] \
\fI\|file\fP [\fIwidth\fP [\,\fIheight\/\fP]]
.RE
.
.
.IP
.I file
is the name of the PostScript file;
.I width
and
.I height
give the desired width and height of the image.
.
If neither a
.I width
nor a
.I height
argument is specified,
the image's natural width
(as given in the file's bounding box)
or the current line length is used as the width,
whatever is smaller.
.
The
.I width
and
.I height
arguments may have scaling units attached;
the default scaling unit
.RB is\~ i .
.
.B PSPIC
scales the graphic uniformly in the horizontal and vertical directions
so that it is no more than
.I width
wide
and
.I height
high.
.
Option
.B \-C
centers the graphic horizontally;
this is the default.
.
.B \-L
and
.B \-R
left- and right-align the graphic,
respectively.
.
.B \-I
indents the graphic
.RI by\~ n
(with a default scaling unit
.RB of\~ m ).
.
.
.IP
To use
.B PSPIC
within a diversion,
we recommend extending it with the following code,
assuring that the diversion's width completely covers the image's width.
.
.
.RS
.IP
.EX
\&.am PSPIC
\&.\~\~vpt 0
\&\[rs]h\[aq](\[rs]\[rs]n[ps\-offset]u + \[rs]\[rs]n[ps\-deswid]u)\[aq]
\&.\~\~sp \-1
\&.\~\~vpt 1
\&..
.EE
.RE
.
.
.IP
Failure to load
.BR PSPIC 's
image argument is not an error.
.
(The
.B psbb
request does issue an error diagnostic.)
.
To make such a failure fatal,
append to the
.B pspic*error\-hook
macro.
.
.
.RS
.IP
.EX
\&.am pspic*error\-hook
\&.\~\~ab
\&..
.EE
.RE
.
.
.TP
.I ptx
provides a macro,
.BR xx ,
to format permuted index entries as produced by the GNU
.MR ptx 1
program.
.
If your formatting needs differ,
copy the macro into your document and adapt it to your needs.
.
.
.TP
.I rfc1345
defines special character escape sequences named for the glyph mnemonics
specified in RFC\~1345 and the digraph table of the Vim text editor.
.
See
.MR groff_rfc1345 7 .
.
.
.TP
.I sboxes
offers an interface to the
.RB \[lq] "pdf: background" \[rq]
device control command supported by
.MR gropdf 1 .
.
Using this package,
.I groff ms
documents can draw colored rectangles beneath any output.
.
.RS
.TP
.BI \%.BOXSTART\~SHADED\~ color\~\c
.BI \%OUTLINED\~ color\~\c
.BI \%INDENT\~ size\~\c
.BI \%WEIGHT\~ size
begins a box,
where the argument after
.B \%SHADED
gives the fill color and that after
.B \%OUTLINED
the border color.
.
Omit the former to get a borderless filled box and the latter for a
border with no fill.
.
The specified
.B \%WEIGHT
is used if the box is
.BR \%OUTLINED .
.
.
.IP
.B \%INDENT
precedes a value which leaves a gap between the border and the contents
inside the box.
.
.
.IP
Each
.I color
must be a defined
.I groff
color name,
and each
.I size
a valid
.I groff
numeric expression.
.
The keyword/value pairs can be specified in any order.
.RE
.
.
.IP
Boxes can be stacked,
so you can start a box within another box;
usually the later boxes would be smaller than the containing box,
but this is not enforced.
.
When using
.BR \%BOXSTART ,
the left position is the current indent minus the
.B \%INDENT
in the command,
and the right position is the left position
(calculated above)
plus the current line length and twice the indent.
.
.
.RS
.TP
.B \%.BOXSTOP
takes no parameters.
.
It closes the most recently started box at the current vertical position
after adding its
.B \%INDENT
spacing.
.RE
.
.
.IP
Your
.I groff
documents can conditionally exercise the
.I sboxes
macros.
.
The register
.B \%GSBOX
is defined if the package is loaded,
and interpolates a true value if the
.B pdf
output device is in use.
.
.
.IP
.I sboxes
furthermore hooks into the
.MR groff_ms 7
package to receive notifications when footnotes are growing,
so that it can close boxes on a page before footnotes are printed.
.
When that condition obtains,
.I sboxes
will close open boxes two points
above the footnote separator and re-open them on the next page.
.
(This amount probably will not match the box's
.BR \%INDENT .)
.
.
.IP
See
.UR file:///usr/\:\%share/\:\%doc/\:\%groff\-base/\:\%msboxes\:.pdf
\[lq]Using PDF boxes with
.I groff
and the
.I ms
macros\[rq]
.UE
for a demonstration.
.
.
.TP
.I trace
aids the debugging of
.I groff
documents by tracing macro calls.
.
See
.MR groff_trace 7 .
.
.
.TP
.I www
defines macros corresponding to HTML elements.
.
See
.MR groff_www 7 .
.
.
.\" ====================================================================
.SH Naming
.\" ====================================================================
.
AT&T
.I nroff \" AT&T
and
.I troff \" AT&T
were implemented before the conventions of the modern C
.MR getopt 3
call evolved,
and used a naming scheme for macro packages that looks odd to modern
eyes.
.
Macro packages were typically loaded using the
.B \-m
option to the formatter;
when directly followed by its argument without an intervening space,
this looked like a long option preceded by a single minus\[em]a
sensation in the computer stone age.
.
Macro packages therefore came to be known by names that started with the
letter \[lq]m\[rq],
which was omitted from the name of the macro file as stored on disk.
.
For example,
the manuscript macro package was stored as
.I tmac.s
and loaded with the option
.BR \-ms .
.
.
.P
.I groff
commands permit space between an option and its argument.
.
The syntax
.RB \[lq] "groff \-m s" \[rq]
makes the macro file name more clear but may surprise users familiar
with the original convention,
unaware that the package's \[lq]real\[rq] name was \[lq]s\[rq] all
along.
.
For such packages of long pedigree,
.I groff
accommodates different users' expectations by supplying wrapper macro
files that load the desired file with
.B mso
requests.
.
Thus,
all of
.RB \[lq] "groff \-m s" \[rq],
.RB \[lq] "groff \-m ms" \[rq],
.RB \[lq] "groff \-ms" \[rq],
and
.RB \[lq] "groff \-mms" \[rq]
serve to load the manuscript macros.
.
.
.P
Wrappers are not provided for packages of more recent vintage,
like
.IR www.tmac .
.
.
.P
As noted in passing above,
AT&T
.I troff \" AT&T
named macro files in the form
.IR tmac. name.
.
It has since become conventional in operating systems to use a suffixed
file name extension to suggest a file type or format.
.
.
.\" ====================================================================
.SH Inclusion
.\" ====================================================================
.
The traditional method of employing a macro package is to specify the
.B \-m
.I package
option to the formatter,
which then reads
.IR package 's
macro file prior to any input files.
.
Historically,
.I package
was sought in a file named
.IR tmac. package
(that is,
with a
.RB \[lq] tmac.\& \[rq]
prefix).
.
GNU
.I troff \" GNU
searches for
.RI package .tmac
in the macro path;
if not found,
it looks for
.IR tmac. package
instead,
and vice versa.
.
.
.P
Alternatively,
one could include a macro file by using the request
.RB \[lq] .so
.IR file-name \[rq]
in the document;
.I file-name
is resolved relative to the location of the input document.
.
GNU
.I troff \" GNU
offers an improved feature in the similar request
.RB \[lq] mso
.IR package-file-name \[rq],
which searches the macro path for
.IR package-file-name .
.
Because its argument is a file name,
its
.RB \[lq] .tmac \[rq]
component must be included for the file to be found;
however,
as a convenience,
if opening it fails,
.B mso
strips any such suffix and tries again with a
.RB \[lq] tmac.\& \[rq]
prefix,
and vice versa.
.
.
.P
If a sourced file requires preprocessing,
for example if it includes
.I tbl \" generic
tables
or
.I eqn \" generic
equations,
the preprocessor
.MR \%soelim 1
must be used.
.
This can be achieved with a pipeline or,
in
.IR groff ,
by specifying
the
.B \-s
option to the formatter
(or front end).
.
.MR man 1
librarian programs generally call
.I \%soelim
automatically.
.
(Macro packages themselves generally do not require preprocessing.)
.
.
.ig
.\" ====================================================================
.SH Convention
.\" ====================================================================
.
.\" This section does not fit into the framework of this document.
.
There is a convention that is supported by many modern roff
typesetters and
.MR man 1
programs, the
.I preprocessor word
described in the following.
.
.P
If the first line in a document is a comment, the first word (after the
comment characters and a blank) constitutes the
.B preprocessor
.BR word .
That means that the letters of this word are interpreted as
abbreviations for those preprocessor commands that should be run
when formatting the document.
.
Mostly, only the letters corresponding to the options for the
preprocessors are recognized,
\[oq]e\[cq]
(for
.IR eqn ),
.\" \[oq]G\[cq],
.\" \[oq]g\[cq],
\[oq]p\[cq]
(for
.IR pic ),
\[oq]R\[cq]
(for
.IR refer ),
\[oq]s\[cq]
(for
.IR soelim ),
and
\[oq]t\[cq]
(for
.IR tbl ).
(see
.MR roff 7 ).
.
.
.P
Besides being a good reminder for the user, some formatters (like the
.MR man 1
program) are even able to automatically start the preprocessors
specified in the preprocessor word, but do not bet on this.
.
.
.P
The
.I man
program handles some preprocessors automatically, such that in
man\~pages only the following characters should be used:
\[oq]e\[cq], \[oq]p\[cq], and \[oq]t\[cq].
.
.
..
.\" ====================================================================
.SH "Writing macros"
.\" ====================================================================
.
A
.MR roff 7
document is a text file that is enriched by predefined formatting
constructs, such as requests, escape sequences, strings, numeric
registers, and macros from a macro package.
.
These elements are described in
.MR roff 7 .
.
.
.P
To give a document a personal style, it is most useful to extend the
existing elements by defining some macros for repeating tasks; the best
place for this is near the beginning of the document or in a separate
file.
.
.
.P
Macros without arguments are just like strings.
.
But the full power of macros occurs when arguments are passed with a
macro call.
.
Within the macro definition, the arguments are available as the escape
sequences
.BR \[rs]$1 ,
\&.\|.\|.,
.BR \[rs]$9 ,
.BR \[rs]$[ .\|.\|. ] ,
.BR \[rs]$* ,
and
.BR \[rs]$@ ,
the name under which the macro was called is in
.BR \[rs]$0 ,
and the number of arguments is in register
.BR \[rs]n[.$] ;
see
.MR groff 7 .
.
.
.\" ====================================================================
.SS "Draft mode"
.\" ====================================================================
.
Writing groff macros is easy when the escaping mechanism is temporarily
disabled.
.
In groff, this is done by enclosing the macro definition(s) within a
pair of
.B .eo
and
.B .ec
requests.
.
Then the body in the macro definition is just like a normal part of
the document \[em] text enhanced by calls of requests, macros,
strings, registers, etc.
.
For example, the code above can be written in a simpler way by
.
.
.IP
.ds @1 \[rs]f[I]\[rs]$0\[rs]f[]\"
.ds @2 arguments:\"
.EX
\&.eo
\&.ds midpart was called with the following
\&.de print_args
\&\*[@1]\ \[rs]*[midpart]\ \[rs]n[.$]\ \*[@2]
\&\[rs]$*
\&..
\&.ec
.EE
.rm @1
.rm @2
.
.
.P
Unfortunately, draft mode cannot be used universally.
.
Although it is good enough for defining normal macros, draft mode
fails with advanced applications, such as indirectly defined
strings, registers, etc.
.
An optimal way is to define and test all macros in draft mode and then
do the backslash doubling as a final step; do not forget to remove the
.I .eo
request.
.
.
.\" ====================================================================
.SS "Tips for macro definitions"
.\" ====================================================================
.
.IP \(bu
Start every line with a dot, for example, by using the groff request
.B .nop
for text lines, or write your own macro that handles also text lines
with a leading dot.
.
.RS
.IP
.EX
\&.de Text
\&.\ \ if (\[rs]\[rs]n[.$] == 0)\ \[rs]
\&.\ \ \ \ return
\&.\ \ nop\ \[rs])\[rs]\[rs]$*\[rs])
\&..
.EE
.RE
.
.IP \(bu
Write a comment macro that works both for copy and draft modes;
since the escape character is off in draft mode,
trouble might occur when comment escape sequences are used.
.
For example, the following macro just ignores its arguments, so it
acts like a comment line:
.
.RS
.IP
.EX
\&.de\ c
\&..
\&.c\ This\ is\ like\ a\ comment\ line.
.EE
.RE
.
.IP \(bu
In long macro definitions, make ample use of comment lines or
almost-empty lines (this is, lines which have a leading dot
and nothing else) for a better structuring.
.
.IP \(bu
To increase readability, use groff's indentation facility for
requests and macro calls (arbitrary whitespace after the leading dot).
.
.
.\" ====================================================================
.SS Diversions
.\" ====================================================================
.
Diversions can be used to implement quite advanced programming
constructs.
.
They are comparable to pointers to large data structures in the
C\~programming language, but their usage is quite different.
.
.
.P
In their simplest form, diversions are multi-line strings, but
diversions get their power when used dynamically within macros.
.
The (formatted) information stored in a diversion can be retrieved by
calling the diversion just like a macro.
.
.
.P
Most of the problems arising with diversions can be avoided if you
remember that diversions always store complete lines.
.
Using diversions when the line buffer has not been flushed produces
strange results; not knowing this, many people get desperate about
diversions.
.
To ensure that a diversion works, add line breaks at the right
places.
.
To be safe, enclose everything that has to do with diversions within
a pair of line breaks; for example, by explicitly using
.B .br
requests.
.
This rule should be applied to diversion definition, both inside and
outside, and to all calls of diversions.
.
This is a bit of overkill, but it works nicely.
.
.
.P
(If you really need diversions which should ignore the current partial
line, use environments to save the current partial line and/\:or use the
.B .box
request.)
.
.
.P
The most powerful feature using diversions is to start a diversion
within a macro definition and end it within another macro.
.
Then everything between each call of this macro pair is stored within
the diversion and can be manipulated from within the macros.
.
.
.\" ====================================================================
.SH Authors
.\" ====================================================================
.
This document was written by
.MT groff\-bernd\:.warken\-72@\:web\:.de
Bernd Warken
.ME ,
.MT wl@\:gnu\:.org
Werner Lemberg
.ME ,
and
.MT g.branden\:.robinson@\:gmail\:.com
G.\& Branden Robinson
.ME .
.
.
.\" ====================================================================
.SH "See also"
.\" ====================================================================
.
.IR "Groff: The GNU Implementation of troff" ,
by Trent A.\& Fisher and Werner Lemberg,
is the primary
.I groff
manual.
.
You can browse it interactively with \[lq]info groff\[rq].
.
.
.LP
The
.UR https://\:wiki\:.linuxfoundation\:.org/\:lsb/\:fhs
Filesystem Hierarchy Standard
.UE
is maintained by the Linux Foundation.
.
.
.TP
.MR groff 1
is an overview of the
.I groff
system.
.
.
.TP
.MR groff_man 7 ,
.TQ
.MR groff_mdoc 7 ,
.TQ
.MR groff_me 7 ,
.TQ
.MR groff_mm 7 ,
.TQ
.MR groff_mom 7 ,
.TQ
.MR groff_ms 7 ,
.TQ
.MR groff_rfc1345 7 ,
.TQ
.MR groff_trace 7 ,
\~and
.TQ
.MR groff_www 7
are
.I groff
macro packages.
.
.
.TP
.MR groff 7
summarizes the language recognized by GNU
.IR troff . \" GNU
.
.
.TP
.MR troff 1
documents the default macro file search path.
.
.
.\" Restore compatibility mode (for, e.g., Solaris 10/11).
.cp \n[*groff_groff_tmac_5_man_C]
.do rr *groff_groff_tmac_5_man_C
.
.
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