path: root/man/groff.7.man

'\" t
.TH groff @MAN7EXT@ "@MDATE@" "groff @VERSION@"
.SH Name
groff \- GNU
.I roff
language reference
.
.
.\" ====================================================================
.\" Legal Terms
.\" ====================================================================
.\"
.\" Copyright (C) 2000-2023 Free Software Foundation, Inc.
.\"
.\" This file is part of groff, the GNU roff type-setting system.
.\"
.\" 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 no Front-Cover Texts,
.\" 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.
.
.
.\" Save and disable compatibility mode (for, e.g., Solaris 10/11).
.do nr *groff_groff_7_man_C \n[.cp]
.cp 0
.
.\" Define fallback for groff 1.23's MR macro if the system lacks it.
.nr do-fallback 0
.if !\n(.f           .nr do-fallback 1 \" mandoc
.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]  \{\
.  de MR
.    ie \\n(.$=1 \
.      I \%\\$1
.    el \
.      IR \%\\$1 (\\$2)\\$3
.  .
.\}
.rr do-fallback
.
.
.\" ====================================================================
.\" Setup
.\" ====================================================================
.
.\" Man pages should not define page-local macros.  Most of these were
.\" written long ago; someday we'll revise the page without them.
.
.\" ====================================================================
.\" start a macro, escape sequence, or register definition
.
.de TPx
.  TP 10n
..
.\" ====================================================================
.\" .Text anything ...
.\"
.\" All arguments are printed as text.
.\"
.de Text
.  nop \)\\$*
..
.
.\" ========= characters =========
.
.de squoted_char
.  Text \[oq]\f[CB]\\$1\f[]\[cq]\\$2
..
.de dquoted_char
.  Text \[lq]\f[CB]\\$1\f[]\[rq]\\$2
..
.\" ========= requests =========
.
.\" synopsis of a request
.de REQ
.  ie \\n[.$]=1 \{\
.    Text \f[CB]\\$1\f[]
.  \}
.  el \{\
.    Text \f[CB]\\$1\~\f[]\f[I]\\$2\f[]
.  \}
..
.
.\" reference of a request
.de request
.  ie (\\n[.$] < 2) \
.    B \\$*
.  el \
.    BR \\$*
..
.
.\" ========= numeric elements =========
.
.\" number with a trailing unit
.de scalednumber
.  Text \\$1\^\f[CB]\\$2\f[]\\$3\f[R]
.  ft P
..
.
.\" representation of units within the text
.de scaleindicator
.  Text \f[CB]\\$1\f[]\\$2\f[R]
.  ft P
..
.
.\" representation of mathematical operators within the text
.de operator
.  squoted_char \\$@
..
.
.
.\" ========= escape sequences =========
.
.\" ====================================================================
.\" .ESC name [arg]
.\"
.\" Synopsis of an escape sequence, optionally with argument
.\" Args   : 1 or 2; 'name' obligatory, 'arg' optional
.\"   name : suitable name for an escape sequence (c, (xy, [long])
.\"   arg  : arbitrary word
.\" Result : prints \namearg, where 'name' is in CB, 'arg' in I
.\"
.de ESC
.  Text "\f[CB]\e\\$1\,\f[I]\\$2\/\fR"
..
.\" ====================================================================
.\" .ESC[] name arg
.\"
.\" Synopsis for escape sequence with a bracketed long argument
.\" Args   : 2 obligatory
.\"   name : suitable name for an escape sequence (c, (xy, [long])
.\"   arg  : arbitrary text
.\" Result : prints \name[arg], where 'name' is in CB, 'arg' in I
.\"
.de ESC[]
.  Text "\f[CB]\e\\$1\[lB]\f[]\,\f[I]\\$2\/\f[]\f[CB]\[rB]\f[]"
..
.\" ====================================================================
.\" .ESCq name arg
.\"
.\" Synopsis for escape sequence with a bracketed long argument
.\" Args   : 2 obligatory
.\"   name : suitable name for an escape sequence (c, (xy, [long])
.\"   arg  : arbitrary text
.\" Result : prints \name'arg', where 'name' is in CB, 'arg' in I
.\"
.de ESCq
.  Text "\f[CB]\e\\$1\[aq]\f[]\,\f[I]\\$2\/\f[]\f[CB]\[aq]\f[]"
..
.\" ====================================================================
.\" .ESC? arg
.\"
.\" Synopsis for escape sequence with a bracketed long argument
.\" Args   : 1 obligatory
.\"   arg  : arbitrary text
.\" Result : prints '\?arg\?', where the '\?' are in CB, 'arg' in I
.\"
.de ESC?
.  Text "\f[CB]\e?\,\f[I]\\$1\/\f[CB]\[rs]?\f[R]"
..
.\" ====================================================================
.\" .esc name [punct]
.\"
.\" Reference of an escape sequence (no args), possibly punctuation
.\" Args    : 1 obligatory
.\"   name  : suitable name for an escape sequence (c, (xy, [long])
.\"   punct : arbitrary
.\" Result  : prints \name, where 'name' is in B, 'punct' in R
.\"
.de esc
.  ie (\\n[.$] < 2) \
.    B "\e\\$1"
.  el \
.    BR "\e\\$1" \\$2
..
.\" ====================================================================
.\" .escarg name arg [punct]
.\"
.\" Reference of an escape sequence (no args)
.\" Args    : 1 obligatory, 1 optional
.\"   name  : suitable name for an escape sequence (c, (xy, [long])
.\"   arg   : arbitrary word
.\" Result  : prints \namearg, where
.\"           'name' is in B, 'arg' in I
.\"
.de escarg
.  Text \f[B]\e\\$1\f[]\,\f[I]\\$2\/\f[]\\$3
..
.\" ====================================================================
.\" .esc[] name arg [punct]
.\"
.\" Reference for escape sequence with a bracketed long argument
.\" Args   : 2 obligatory
.\"   name : suitable name for an escape sequence (c, (xy, [long])
.\"   arg  : arbitrary text
.\" Result : prints \name[arg], where 'name' is in CB, 'arg' in CI
.\"
.de esc[]
.  Text \f[CB]\e\\$1\[lB]\f[]\,\f[CI]\\$2\/\f[]\f[CB]\[rB]\f[]\\$3
..
.
.\" ========= strings =========
.
.\" synopsis for string, with \*[]
.de STRING
.  Text \[rs]*[\f[CB]\\$1\f[]] \\$2
..
.\" synopsis for a long string
.de string
.  if \n[.$]=0 \
.    return
.  Text \f[CB]\[rs]*\[lB]\\$1\[rB]\f[]\\$2
..
.
.\" ========= registers =========
.
.\" synopsis for registers, with \n[]
.de REG
.  Text \[rs]n[\f[CB]\\$1\f[]]
..
.\" reference of a register, without decoration
.de register
.  Text register
.  ie (\\n[.$] < 2) \
.    B \\$*
.  el \
.    BR \\$*
..
.
.\" begin list [piloting a possible extension to man(7)]
.de LS
.  nr saved-PD \\n[PD]
.  nr PD 0
..
.
.\" end list [piloting a possible extension to man(7)]
.de LE
.  nr PD \\n[saved-PD]
..
.
.
.\" end of macro definitions
.
.
.\" ====================================================================
.SH Description
.\" ====================================================================
.
.I groff
is short for GNU
.IR roff ,
a free reimplementation of the AT&T device-independent
.I troff \" AT&T
typesetting system.
.
See
.MR roff @MAN7EXT@
for a survey of and background on
.I roff
systems.
.
.
.P
This document is intended as a reference.
.
The primary
.I groff
manual,
.IR "Groff: The GNU Implementation of troff" ,
by Trent A.\& Fisher and Werner Lemberg,
is a better resource for learners,
containing many examples and much discussion.
.
It is written in Texinfo;
you can browse it interactively with \[lq]info groff\[rq].
.
Additional formats,
including plain text,
HTML,
DVI,
and PDF,
may be available in
.IR @DOCDIR@ .
.
.
.P
.I groff
is also a name for an extended dialect of the
.I roff
language.
.
We use \[lq]roff\[rq] to denote features that are universal,
or nearly so,
among implementations of this family.
.
We apply the term \[lq]groff\[rq] to the language documented here,
the GNU implementation of the overall system,
the project that develops that system,
and the command of that name.
.
.
.P
GNU
.IR troff , \" GNU
installed on this system as
.MR @g@troff @MAN1EXT@ ,
is the
.I formatter:
a program that reads device and font descriptions
(\c
.MR groff_font @MAN5EXT@ ),
interprets the
.I groff
language expressed in text input files,
and translates that input into a device-independent output format
(\c
.MR groff_out @MAN5EXT@ )
that is usually then post-processed by an output driver to produce
PostScript,
PDF,
HTML,
DVI,
or terminal output.
.
.
.\" ====================================================================
.SH "Input format"
.\" ====================================================================
.
Input to GNU
.I troff \" GNU
is organized into lines separated by the Unix newline character
(U+000A),
and must be in one of two character encodings it can recognize:
IBM code page 1047 on EBCDIC systems,
and ISO\~Latin-1 (8859-1) otherwise.
.
Use of ISO\~646-1991:IRV (\[lq]US-ASCII\[rq]) or (equivalently) the
\[lq]Basic Latin\[rq]
subset of ISO\~10646 (\[lq]Unicode\[rq]) is recommended;
see
.MR groff_char @MAN7EXT@ .
.
The
.MR preconv @MAN1EXT@
preprocessor transforms other encodings,
including UTF-8,
to satisfy
.IR @g@troff 's
requirements.
.
.
.\" ====================================================================
.SH "Syntax characters"
.\" ====================================================================
.
Several input characters are syntactically significant to
.IR groff .
.
.
.IP . 4n
A dot at the beginning of an input line marks it as a
.I control line.
.
It can also follow the
.request .el
and
.request .nop
requests,
and the condition in
.request .if ,
.request .ie ,
and
.request .while
requests.
.
The control character invokes requests and calls macros by the name that
follows it.
.
The
.request .cc
request can change the control character.
.
.
.IP \[aq]
The neutral apostrophe is the
.I "no-break control character,"
recognized where the control character is.
.
It suppresses the (first) break implied by the
.request .bp ,
.request .cf ,
.request .fi ,
.request .fl ,
.request .in ,
.request .nf ,
.request .rj ,
.request .sp ,
.request .ti ,
and
.request .trf
requests.
.
The requested operation takes effect at the next break.
.
It makes
.request .br
nilpotent.
.
The no-break control character can be changed with the
.request .c2
request.
.
When formatted,
.RB \[lq] \[aq] \[rq]
may be typeset as a typographical quotation mark;
use the
.esc [aq]
special character escape sequence to format a neutral apostrophe glyph.
.
.
.IP \[dq]
The neutral double quote can be used to enclose arguments to macros and
strings,
and is required if those arguments contain space or tab characters.
.
In the
.request .ds ,
.request .ds1 ,
.request .as ,
and
.request .as1
requests,
an initial neutral double quote in the second argument is stripped off
to allow embedding of leading spaces.
.
To include a double quote inside a quoted argument,
use the
.esc [dq]
special character escape sequence
(which also serves to typeset the glyph in text).
.
.
.IP \[rs]
A backslash introduces an escape sequence.
.
The escape character can be changed with the
.request .ec
request;
.request .eo
disables escape sequence recognition.
.
Use the
.esc [rs]
special character escape sequence to format a backslash glyph,
and
.esc e
to typeset the glyph of the current escape character.
.
.
.IP (
An opening parenthesis is special only in certain escape sequences;
when recognized,
it introduces an argument of exactly two characters.
.
.I groff
offers the more flexible square bracket syntax.
.
.
.IP [
An opening bracket is special only in certain escape sequences;
when recognized,
it introduces an argument (list) of any length,
not including a closing bracket.
.
.
.IP ]
A closing bracket is special only when an escape sequence using an
opening bracket as an argument delimiter is being interpreted.
.
It ends the argument (list).
.
.
.P
Additionally,
the Control+A character (U+0001) in text is interpreted as a
.I leader
(see below).
.
.
.P
Horizontal white space characters are significant to
.I groff,
but trailing spaces on text lines are ignored.
.\" slack text for widow/orphan control: trailing tabs are not
.
.
.TP 8n
.I space
Space characters separate arguments in request invocations,
macro calls,
and string interpolations.
.
In text,
they separate words.
.
Multiple adjacent space characters in text cause
.I groff
to attempt end-of-sentence detection on the preceding word
(and trailing punctuation).
.
The amount of space between words and sentences is controlled by the
.request .ss
request.
.
When filling is enabled
(the default),
a line may be broken at a space.
.
When adjustment is enabled
(the default),
inter-word spaces are expanded until the output line reaches the
configured length.
.
An adjustable but non-breaking space is available with
.esc \[ti] .
.
To get a space of fixed width,
use one of the escape sequences
.squoted_char "\[rs]\~"
(the escape character followed by a space),
.esc 0 ,
.esc | ,
.esc \[ha] ,
or
.esc h ;
see section \[lq]Escape sequences\[rq] below.
.
.
.TP
.I newline
In text,
a newline puts an inter-word space onto the output and,
if filling is enabled,
triggers end-of-sentence recognition on the preceding text.
.
See section \[lq]Line continuation\[rq] below.
.
.
.TP
.I tab
A tab character in text causes the drawing position to advance to the
next defined tab stop.
.
.
.\" ====================================================================
.SH "Tabs and leaders"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Tabs and
.\" Leaders".
The formatter interprets input horizontal tab characters
(\[lq]tabs\[rq]) and Control+A characters (\[lq]leaders\[rq]) into
movements to the next tab stop.
.
Tabs simply move to the next tab stop;
leaders place enough periods to fill the space.
.
Tab stops are by default located every half inch measured from the
drawing position corresponding to the beginning of the input line;
see section \[lq]Page geometry\[rq] of
.MR roff 7 .
.
Tabs and leaders do not cause breaks and therefore do not interrupt
filling.
.
Tab stops can be configured with the
.B ta
request,
and tab and leader glyphs with the
.B tc
and
.B lc
requests,
respectively.
.\" END Keep (roughly) parallel with groff.texi node "Tabs and Leaders".
.
.
.\" ====================================================================
.SH "Line continuation"
.\" ====================================================================
.
When filling is enabled,
input and output line breaks generally do not correspond.
.
The
.I roff
language therefore distinguishes input and output line continuation.
.
.
.P
A backslash
.B \[rs]
immediately followed by a newline,
sometimes discussed as
.BI \[rs] newline\c
,
suppresses the effects of that newline
on the input.
.
The next input line thus retains the classification of its predecessor
as a control or text line.
.
.BI \[rs] newline
is useful for managing line lengths in the input during document
maintenance;
you can break an input line in the middle of a request invocation,
macro call,
or escape sequence.
.
Input line continuation is invisible to the formatter,
with two exceptions:
the
.B \[or]
operator recognizes the new input line,
and the input line counter register
.B .c
is incremented.
.
.
.P
The
.esc c
escape sequence continues an
.I output
line.
.
Nothing on the input line after it is formatted.
.
In contrast to
.BI \[rs] newline\c
,
a line after
.esc c
is treated as a new input line,
so a control character is recognized at its beginning.
.
The visual results depend on whether filling is enabled.
.
An intervening control line that causes a break overrides
.esc c ,
flushing out the pending output line in the usual way.
.
The
.register .int
contains a positive value if the last output line was continued with
.esc c ;
this datum is associated with the
environment.
.
.
.\" ====================================================================
.SH Colors
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Colors".
.I groff
supports color output with a variety of color spaces and up to 16 bits
per channel.
.
Some devices,
particularly terminals,
may be more limited.
.
When color support is enabled,
two colors are current at any given time:
the
.I stroke color,
with which glyphs,
rules (lines),
and geometric objects like circles and polygons are drawn,
and the
.I fill color,
which can be used to paint the interior of a closed geometric figure.
.
The
.BR color ,
.BR defcolor ,
.BR gcolor ,
and
.B fcolor
requests;
.B \[rs]m
and
.B \[rs]M
escape sequences;
and
.BR .color ,
.BR .m ,
and
.B .M
registers exercise color support.
.
.
.P
Each output device has a color named
.RB \[lq] default \[rq],
which cannot be redefined.
.
A device's default stroke and fill colors are not necessarily the same.
.
For the
.BR dvi ,
.BR html ,
.BR pdf ,
.BR ps ,
and
.B xhtml
output devices,
.I @g@troff
automatically loads a macro file defining many color names at startup.
.
By the same mechanism,
the devices supported by
.MR grotty @MAN1EXT@
recognize the eight standard ISO\~6429/ECMA-48 color names
(also known vulgarly as \[lq]ANSI colors\[rq]).
.\" END Keep (roughly) parallel with groff.texi node "Colors".
.
.
.br
.ne 3v
.\" ====================================================================
.SH Measurements
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Measurements".
Numeric parameters that specify measurements are expressed as
integers or decimal fractions with an optional
.I scaling unit
suffixed.
.
A scaling unit is a letter that immediately follows the last digit of a
number.
.
Digits after the decimal point are optional.
.
.
.P
Measurements are scaled by the scaling unit and stored internally
(with any fractional part discarded)
in basic units.
.
The device resolution can therefore be obtained by storing a value of
.RB \[lq] 1i \[rq]
to a register.
.
The only constraint on the basic unit is that it is at least as small as
any other unit.
.\" That's a fib.  A device resolution of around 2^31 would surely also
.\" cause problems.  But nobody does that.
.
.
.P
.LS
.TP
.B u
Basic unit.
.
.TP
.B i
Inch;
defined as 2.54\~centimeters.
.
.TP
.B c
Centimeter.
.
.TP
.B p
Point;
a typesetter's unit used for measuring type size.
.
There are 72\~points to an inch.
.
.TP
.B P
Pica;
another typesetter's unit.
.
There are 6\~picas to an inch and 12\~points to a pica.
.
.TP
.BR s ,\~ z
Scaled points and multiplication by the output device's
.I sizescale
parameter,
respectively.
.
.TP
.B f
Multiplication by 65,536;
.
scales decimal fractions in the interval [0, 1] to 16-bit unsigned
integers.
.LE
.
.
.P
The magnitudes of other scaling units depend on the text formatting
parameters in effect.
.
.
.P
.LS
.TP
.B m
Em;
an em is equal to the current type size in points.
.
.TP
.B n
En;
an en is one-half em.
.
.TP
.B v
Vee;
distance between text baselines.
.
.TP
.B M
Hundredth of an em.
.LE
.\" END Keep (roughly) parallel with groff.texi node "Measurements".
.
.
.\" ====================================================================
.SS "Motion quanta"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Motion Quanta".
An output device's basic unit
.B u
is not necessarily its smallest addressable length;
.B u
can be smaller to avoid problems with integer roundoff.
.
The minimum distances that a device can work with in the horizontal and
vertical directions are termed its
.I "motion quanta,"
stored in the
.B .H
and
.B .V
registers,
respectively.
.
Measurements are rounded to applicable motion quanta.
.
Half-quantum fractions round toward zero.
.\" END Keep (roughly) parallel with groff.texi node "Motion Quanta".
.
.
.\" ====================================================================
.SS "Default units"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Default Units".
A general-purpose register
(one created or updated with the
.B nr
request;
see section \[lq]Registers\[rq] below)
is implicitly dimensionless,
or reckoned in basic units if interpreted in a measurement context.
.
But it is convenient for many requests and escape sequences to infer a
scaling unit for an argument if none is specified.
.
An explicit scaling unit
(not after a closing parenthesis)
can override an undesirable default.
.
Effectively,
the default unit is suffixed to the expression if a scaling unit is not
already present.
.
GNU
.IR troff 's \" GNU
use of integer arithmetic should also be kept in mind;
see below.
.\" END Keep (roughly) parallel with groff.texi node "Default Units".
.
.
.\" ====================================================================
.SH "Numeric expressions"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Numeric
.\" expressions".
A
.I numeric expression
evaluates to an integer.
.
The following operators are recognized.
.\"evaluates to an integer:
.\"it can be as simple as a literal
.\".RB \[lq] 0 \[rq]
.\"or it can be a complex sequence of register and string interpolations
.\"interleaved with measurement operators.
.
.
.P
.TS
Rf(CR) L.
+	addition
\-	subtraction
*	multiplication
/	truncating division
%	modulus
_
\f[R]unary\f[] +	assertion, motion, incrementation
\f[R]unary\f[] \-	negation, motion, decrementation
_
;	scaling
>?	maximum
<?	minimum
_
<	less than
>	greater than
<=	less than or equal
>=	greater than or equal
\&=	equal
==	equal
_
&	logical conjunction (\[lq]and\[rq])
:	logical disjunction (\[lq]or\[rq])
!	logical complementation (\[lq]not\[rq])
_
( )	precedence
_
|	boundary-relative motion
.TE
.
.
.P
.I @g@troff
provides a set of mathematical and logical operators familiar to
programmers\[em]as well as some unusual ones\[em]but supports only
integer arithmetic.
.
(Provision is made for interpreting and
reporting decimal fractions in certain cases.)
.
The internal data type used for computing results is usually a 32-bit
signed integer,
which suffices to represent magnitudes within a range of \[+-]2
billion.
.
(If that's not enough, see
.MR groff_tmac @MAN5EXT@
for the
.I 62bit.tmac
macro package.)
.
.
.P
Arithmetic infix operators perform a function on the numeric expressions
to their left and right;
they are
.B +
(addition),
.B \-
(subtraction),
.B *
(multiplication),
.B /
(truncating division),
and
.B %
(modulus).
.
.I Truncating division
rounds to the integer nearer to zero,
no matter how large the fractional portion.
.
Overflow and division
(or modulus)
by zero are errors and abort evaluation of a numeric expression.
.
.
.P
Arithmetic unary operators operate on the numeric expression to their
right;
they are
.B \-
(negation)
and
.B +
(assertion\[em]for completeness;
it does nothing).
.
The unary minus must often be used with parentheses to avoid confusion
with the decrementation operator,
discussed below.
.
.
.P
The sign of the modulus of operands of mixed signs is determined by the
sign of the first.
.
Division and modulus operators satisfy the following property:
given a
.RI dividend\~ a
and a
.RI divisor\~ b ,
a
.RI quotient\~ q
formed by
.RB \[lq] "(a / b)" \[rq]
and a
.RI remainder\~ r
by
.RB \[lq] "(a % b)" \[rq],
then
.IR qb \~+\~ r \~=\~ a .
.
.
.P
GNU
.IR troff 's \" GNU
scaling operator,
used with parentheses as
.BI ( c ; e )\c
,
evaluates a numeric
.RI expression\~ e
.RI using\~ c
as the default scaling unit.
.
If
.I c
is omitted,
scaling units are ignored in the evaluation
.RI of\~ e .
.
GNU
.I troff \" GNU
also provides a pair of operators to compute the extrema of two
operands:
.B >?\&
(maximum)
and
.B <?\&
(minimum).
.
.
.P
Comparison operators comprise
.B <
(less than),
.B >
(greater than),
.B <=
(less than or equal),
.B >=
(greater than or equal),
and
.B =
(equal).
.
.B ==
is a synonym for
.BR = .
.
When evaluated,
a comparison is replaced with
.RB \[lq] 0 \[rq]
if it is false and
.RB \[lq] 1 \[rq]
if true.
.
In the
.I roff
language,
positive values are true,
others false.
.
.
.P
We can operate on truth values with the logical operators
.B &
(logical conjunction or \[lq]and\[rq])
and
.B :
(logical disjunction or \[lq]or\[rq]).
.
They evaluate as comparison operators do.
.
A logical complementation (\[lq]not\[rq]) operator,
.B !\&,
works only within
.RB \[lq] if \[rq],
.RB \[lq] ie \[rq],
and
.RB \[lq] while \[rq]
requests.
.
.\" This is worded to avoid implying that the operator doesn't apply to
.\" conditional expressions in general, albeit without mentioning them
.\" because they're out of scope.
Furthermore,
.B !\&
is recognized only at the beginning of a numeric expression not
contained by another numeric expression.
.
In other words,
it must be the \[lq]outermost\[rq] operator.
.
Including it elsewhere in the expression produces a warning in the
.RB \%\[lq] number \[rq]
category
(see
.MR @g@troff @MAN1EXT@ ),
and its expression evaluates false.
.
This unfortunate limitation maintains compatibility with AT&T
.IR troff .\" AT&T
.
Test a numeric expression for falsity by comparing it to a false value.
.
.
.P
The
.I roff
language has no operator precedence:
expressions are evaluated strictly from left to right,
in contrast to schoolhouse arithmetic.
.
Use parentheses
.B ( )
to impose a desired precedence upon subexpressions.
.
.
.P
For many requests and escape sequences that cause motion on the page,
the unary operators
.B +
and
.B \-
work differently when leading a numeric expression.
.
They then indicate a motion relative to the drawing position:
positive is down in vertical contexts,
right in horizontal ones.
.
.
.P
.B +
and
.B \-
are also treated differently by the following requests and escape
sequences:
.BR bp ,
.BR in ,
.BR ll ,
.BR pl ,
.BR pn ,
.BR po ,
.BR ps ,
.BR pvs ,
.BR rt ,
.BR ti ,
.BR \[rs]H ,
.BR \[rs]R ,
and
.BR \[rs]s .
.
Here,
leading plus and minus signs serve as incrementation and decrementation
operators,
respectively.
.
To negate an expression,
subtract it from zero
or include the unary minus in parentheses with its argument.
.\" @xref{Setting Registers}, for examples.
.
.
.P
A leading
.B \[or]
operator indicates a motion relative not to the drawing position but to
a boundary.
.
For horizontal motions,
the measurement specifies a distance relative to a drawing position
corresponding to the beginning of the
.I input
line.
.
By default,
tab stops reckon movements in this way.
Most escape sequences do not;
.\" XXX: Which ones do?
.B \[or]
tells them to do so.
.
For vertical motions,
the
.B \[or]
operator specifies a distance from the first text baseline on the page
or in the current diversion,
using the current vertical spacing.
.
.
.P
The
.B \[rs]B
escape sequence tests its argument for validity as a numeric expression.
.
.
.br
.ne 2v
.P
A register interpolated as an operand in a numeric expression must have
an Arabic format;
luckily,
this is the default.\" @xref{Assigning Register Formats}.
.
.
.P
Due to the way arguments are parsed,
spaces are not allowed in numeric expressions unless the (sub)expression
containing them is surrounded by parentheses.
.\"@xref{Request and Macro Arguments}, and @ref{Conditionals and Loops}.
.\" END Keep (roughly) parallel with groff.texi node "Numeric
.\" expressions".
.
.
.\" ====================================================================
.SH Identifiers
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Identifiers".
An
.I identifier
labels a GNU
.I troff \" GNU
datum such as a register,
name
(macro,
string,
or diversion),
typeface,
color,
special character,
character class,
environment,
or stream.
.
Valid identifiers consist of one or more ordinary characters.
.
An
.I ordinary character
is an input character that is not the escape character,
a leader,
tab,
newline,
or invalid as GNU
.I troff \" GNU
input.
.
.
.\" XXX: We might move this discussion earlier since it is applicable to
.\" troff input in general, and include a reference to the `trin`
.\" request.
.P
Invalid input characters are subset of control characters
(from the sets \[lq]C0 Controls\[rq] and \[lq]C1 Controls\[rq] as
Unicode describes them).
.
When
.I @g@troff
encounters one in an identifier,
it produces a warning in category
.RB \%\[lq] input \[rq]
(see section \[lq]Warnings\[rq] in
.MR @g@troff @MAN1EXT@ ).
.
They are removed during interpretation:
an identifier \[lq]foo\[rq],
followed by an invalid
character and then \[lq]bar\[rq],
is processed as \[lq]foobar\[rq].
.
.
.P
On a machine using the ISO 646,
8859,
or 10646 character encodings,
invalid input characters are
.BR 0x00 ,
.BR 0x08 ,
.BR 0x0B ,
.BR 0x0D \[en] 0x1F ,
and
.BR 0x80 \[en] 0x9F .
.
On an EBCDIC host,
they are
.BR 0x00 \[en] 0x01 ,
.BR 0x08 ,
.BR 0x09 ,
.BR 0x0B ,
.BR 0x0D \[en] 0x14 ,
.BR 0x17 \[en] 0x1F ,
and
.BR 0x30 \[en] 0x3F .
.
Some of these code points are used by
.I @g@troff
internally,
making it non-trivial to extend the program to accept UTF-8 or other
encodings that use characters from these ranges.
.
.
.P
An identifier with a closing bracket (\[lq]]\[rq]) in its name can't be
accessed with bracket-form escape sequences that expect an identifier as
a parameter.
.
Similarly,
the
identifier \[lq](\[rq] can't be interpolated
.I except
with bracket forms.
.
.
.P
If you begin a macro,
string,
or diversion name with either of the characters \[lq][\[rq] or
\[lq]]\[rq],
you foreclose use of the
.MR @g@refer @MAN1EXT@
preprocessor,
which recognizes \[lq].[\[rq] and \[lq].]\[rq] as bibliographic
reference delimiters.
.
.
.P
The escape sequence
.B \[rs]A
tests its argument for validity as an identifier.
.
.
.P
How GNU
.I troff \" GNU
handles the interpretation of an undefined identifier depends on the
context.
.
There is no way to invoke an undefined request;
such syntax is interpreted as a macro call instead.
.
If the identifier is interpreted as a string,
macro,
or diversion,
.I @g@troff
emits a warning in category
.RB \[lq] mac \[rq],
defines it as empty,
and interpolates nothing.
.
If the identifier is interpreted as a register,
.I @g@troff
emits a warning in category
.RB \[lq] reg \[rq],
initializes it to zero,
and interpolates that value.
.
See section \[lq]Warnings\[rq] in
.MR @g@troff @MAN1EXT@ ,
and subsection \[lq]Interpolating registers\[rq] and section
\[lq]Strings\[rq] below.
.
Attempting to use an undefined
typeface,
style,
special character,
color,
character class,
environment,
or stream generally provokes an error diagnostic.
.
.
.P
Identifiers for requests,
macros,
strings,
and diversions share one name
space;
special characters and character classes another.
.
No other object types do.
.\" END Keep (roughly) parallel with groff.texi node "Identifiers".
.
.
.\" ====================================================================
.SH "Control characters"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Control
.\" Characters".
.\" The mechanism of using @code{roff}'s control characters to invoke
.\" requests and call macros was introduced in @ref{Requests and Macros}.
Control characters are recognized only at the beginning of an input
line,
or at the beginning of the branch of a control structure request;
.\" see @ref{Conditionals and Loops}.
see section \[lq]Control structures\[rq] below.
.
.
.P
A few requests cause a break implicitly;
use the no-break control character to prevent the break.
.
Break suppression is its sole behavioral distinction.
.
Employing the no-break control character to invoke requests that don't
cause breaks is harmless but poor style.
.
.
.P
The control character
.RB \[lq] .\& \[rq]
and the no-break control character
.RB \[lq] \|\[aq]\| \[rq]
can be changed with the
.B cc
and
.B c2
requests,
respectively.
.
Within a macro definition,
.\" you might wish to know
register
.B .br
indicates the control character used to call it.
.\" END Keep (roughly) parallel with groff.texi node "Control
.\" Characters".
.
.
.\" ====================================================================
.SH "Invoking requests"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Invoking
.\" Requests".
A control character is optionally followed by tabs and/or spaces and
then an identifier naming a request or macro.
.
The invocation of an unrecognized request is interpreted as a macro
call.
.
Defining a macro with the same name as a request replaces the request.
.
Deleting a request name with the
.B rm
request makes it unavailable.
.
The
.B als
request can alias requests,
permitting them to be wrapped or non-destructively replaced.
.
See section \[lq]Strings\[rq] below.
.
.
.br
.ne 4v
.P
There is no inherent limit on argument length or quantity.
.
Most requests take one or more arguments,
and ignore any they do not expect.
.
A request may be separated from its arguments by tabs or spaces,
but only spaces can separate an argument from its successor.
.
Only one between arguments is necessary;
any excess is ignored.
.
GNU
.I troff \" GNU
does not allow tabs for argument separation.
.\" @footnote{In compatibility mode, a space is not necessary after a
.\" request or macro name of two characters' length.  Also, Plan@tie{}9
.\" @code{troff} allows tabs to separate arguments.}
.
.
.br
.ne 3v
.P
Generally,
a space
.I within
a request argument is not relevant,
not meaningful,
or is supported by bespoke provisions,
as with the
.B tl
request's delimiters.
.
Some requests,
like
.BR ds ,
interpret the remainder of the control line as a single argument.
.
See section \[lq]Strings\[rq] below.
.
.
.P
Spaces and tabs immediately after a control character are ignored.
.
Commonly,
authors structure the source of documents or macro files with them.
.\" END Keep (roughly) parallel with groff.texi node "Requests".
.
.
.\" ====================================================================
.SH "Calling macros"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Calling Macros".
If a macro of the desired name does not exist when called,
it is created,
assigned an empty definition,
and a warning in category
.RB \[lq] mac \[rq]
is emitted.
.
Calling an undefined macro
.I does
end a macro definition naming it as its end macro
(see section \[lq]Writing macros\[rq] below).
.
.
.P
To embed spaces
.I within
a macro argument,
enclose the argument in neutral double quotes
.RB \[oq] \|\[dq]\| \[cq].
.
Horizontal motion escape sequences are sometimes a better choice for
arguments to be formatted as text.
.
.
.P
The foregoing raises the question of how to embed neutral double quotes
or backslashes in macro arguments when
.I those
characters are desired as literals.
.
In GNU
.IR troff , \" GNU
the special character escape sequence
.B \[rs][rs]
produces a backslash and
.B \[rs][dq]
a neutral double quote.
.
.
.P
In GNU
.IR troff 's \" GNU
AT&T compatibility mode,
these characters remain available as
.B \[rs](rs
and
.BR \[rs](dq ,
respectively.
.
AT&T
.I troff \" AT&T
did not consistently define these special characters,
.\" It seems that AT&T troff never recognized \(rs, though DWB 3.3
.\" defined \(bs as an alias of "\" on its "Latin1" device, in
.\" deliberate(?) collision with the Bell System logo identifier.  It
.\" also defined \(dq for several devices (pcl, Latin1, nroff, ...)
.\" along with \(aq.
but its descendants can be made to support them.
.
See
.MR groff_font @MAN5EXT@ .
.
If even that is not feasible,
.\" Nope nope nope--if you're this much of a masochist, go read Texinfo.
see the \[lq]Calling Macros\[rq] section of the
.I groff
Texinfo manual for the complex macro argument quoting rules of AT&T
.IR troff . \" AT&T
.\" END Keep (roughly) parallel with groff.texi node "Calling Macros".
.
.
.\" ====================================================================
.SH "Using escape sequences"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Using Escape
.\" Sequences".
Whereas requests must occur on control lines,
escape sequences can occur intermixed with text and may appear in
arguments to requests,
macros,
and other escape sequences.
.
An escape sequence is introduced by the escape character,
a backslash
.BR \[rs] .
.\" (but see the @code{ec} request below)
.
The next character selects the escape's function.
.
.
.P
Escape sequences vary in length.
.
Some take an argument,
and of those,
some have different syntactical forms for a one-character,
two-character,
or arbitrary-length argument.
.
Others accept
.I only
an arbitrary-length argument.
.
In the former scheme,
a one-character argument follows the function character immediately,
an opening parenthesis
.RB \[lq] ( \[rq]
introduces a two-character argument
(no closing parenthesis is used),
and an argument of arbitrary length is enclosed in brackets
.RB \[lq] [] \[rq].
.
In the latter scheme,
the user selects a delimiter character.
.
A few escape sequences are idiosyncratic,
and support both of the foregoing conventions
.RB ( \|\[rs]s ),
designate their own termination sequence
.RB ( \|\[rs]? ),
consume input until the next newline
.RB ( \|\[rs]! ,
.BR \|\[rs]" ,
.BR \|\[rs]# ),
or support an additional modifier character
.RB ( \|\[rs]s
again,
and
.BR \|\[rs]n ).
.\" As with requests, use of some escape sequences in source documents
.\" may interact poorly with a macro package you use; consult its
.\" documentation to learn of ``safe'' sequences or alternative
.\" facilities it provides to achieve the desired result.
.
.
.P
If an escape character is followed by a character that does not
identify a defined operation,
the escape character is ignored
(producing
a diagnostic of the
.RB \[lq] escape \[rq]
warning category,
which is not enabled by default)
and the following character is processed normally.
.
.
.P
Escape sequence interpolation is of higher precedence than escape
sequence argument interpretation.
.
This rule affords flexibility in using escape sequences to construct
parameters to other escape sequences.
.
.
.P
The escape character can be interpolated
.RB ( \[rs]e ).
.
Requests permit the escape mechanism to be deactivated
.RB ( eo )
and restored,
or the escape character changed
.RB ( ec ),
and to save and restore it
.RB ( ecs
and
.BR ecr ).
.\" END Keep (roughly) parallel with groff.texi node "Using Escape
.\" Sequences".
.
.
.\" ====================================================================
.SH Delimiters
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Delimiters".
Some escape sequences that require parameters use delimiters.
.
The neutral apostrophe
.B \[aq]
is a popular choice and shown in this document.
.
The neutral double quote
.B \[dq]
is also commonly seen.
.
Letters,
numerals,
and leaders can be used.
.
Punctuation characters are likely better choices,
except for those defined as infix operators in numeric expressions;
see below.
.
.
.br
.ne 2v
.P
The following escape sequences don't take arguments and thus are allowed
as delimiters:
.BI \[rs] space\c
,
.BR \[rs]% ,
.BR \[rs]| ,
.BR \[rs]\[ha] ,
.BR \[rs]{ ,
.BR \[rs]} ,
.BR \[rs]\[aq] ,
.BR \[rs]\[ga] ,
.BR \[rs]\- ,
.BR \[rs]_ ,
.BR \[rs]! ,
.BR \[rs]? ,
.BR \[rs]) ,
.BR \[rs]/ ,
.BR \[rs], ,
.BR \[rs]& ,
.BR \[rs]: ,
.BR \[rs]\[ti] ,
.BR \[rs]0 ,
.BR \[rs]a ,
.BR \[rs]c ,
.BR \[rs]d ,
.BR \[rs]e ,
.BR \[rs]E ,
.BR \[rs]p ,
.BR \[rs]r ,
.BR \[rs]t ,
and
.BR \[rs]u .
.
However,
using them this way is discouraged;
they can make the input confusing to read.
.
.
.P
A few escape sequences,
.BR \[rs]A ,
.BR \[rs]b ,
.BR \[rs]o ,
.BR \[rs]w ,
.BR \[rs]X ,
and
.BR \[rs]Z ,
accept a newline as a delimiter.
.
Newlines that serve as delimiters continue to be recognized as input
line terminators.
.
Use of newlines as delimiters in escape sequences is also discouraged.
.
.
.br
.ne 2v
.P
Finally,
the escape sequences
.BR \[rs]D ,
.BR \[rs]h ,
.BR \[rs]H ,
.BR \[rs]l ,
.BR \[rs]L ,
.BR \[rs]N ,
.BR \[rs]R ,
.BR \[rs]s ,
.BR \[rs]S ,
.BR \[rs]v ,
and
.B \[rs]x
prohibit many delimiters.
.
.
.RS
.IP \[bu] 2n
the numerals 0\[en]9 and the decimal point
.RB \[lq] . \[rq]
.
.
.IP \[bu]
the (single-character) operators
.B +\-/*%<>=&:()
.
.
.IP \[bu]
any escape sequences other than
.BR \[rs]% ,
.BR \[rs]: ,
.BR \[rs]{ ,
.BR \[rs]} ,
.BR \[rs]\[aq] ,
.BR \[rs]\[ga] ,
.BR \[rs]\- ,
.BR \[rs]_ ,
.BR \[rs]! ,
.BR \[rs]/ ,
.BR \[rs]c ,
.BR \[rs]e ,
and
.B \[rs]p
.RE
.
.
.P
Delimiter syntax is complex and flexible primarily for historical
reasons;
the foregoing restrictions need be kept in mind mainly when using
.I groff
in AT&T compatibility mode.
.
GNU
.I troff \" GNU
keeps track of the nesting depth of escape sequence interpolations,
so the only characters you need to avoid using as delimiters are those
that appear in the arguments you input,
not any that result from interpolation.
.
Typically,
.B \[aq]
works fine.
.
See section \[lq]Implementation differences\[rq] in
.MR groff_diff @MAN7EXT@ .
.\" END Keep (roughly) parallel with groff.texi node "Delimiters".
.
.
.\" ====================================================================
.SH "Dummy characters"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Dummy
.\" Characters".
As discussed in
.MR roff @MAN7EXT@ ,
the first character on an input line is treated specially.
.
Further,
formatting a glyph has many
consequences on formatter state
(see section \[lq]Environments\[rq] below).
.
Occasionally,
we want to escape this context or embrace some of those consequences
without actually rendering a glyph to the output.
.
.B \[rs]&
interpolates a dummy character,
which is constitutive of output but invisible.
.
Its presence alters the interpretation context of a subsequent input
character,
and enjoys several applications:
preventing the insertion of extra space after an end-of-sentence
character,
preventing interpretation of a control character at the beginning of an
input line,
preventing kerning between two glyphs,
and permitting the
.B tr
request to remap a character to \[lq]nothing\[rq].
.
.B \[rs])
works as
.B \[rs]&
does,
except that it does not cancel a pending end-of-sentence state.
.\" END Keep (roughly) parallel with groff.texi node "Dummy Characters".
.
.
.\" ====================================================================
.SH "Control structures"
.\" ====================================================================
.
.I groff
has \[lq]if\[rq] and \[lq]while\[rq] control structures like other
languages.
.
However,
the syntax for grouping multiple input lines in the branches or bodies
of these structures is unusual.
.
.
.P
They have a common form:
the request name is
(except for
.request .el
\[lq]else\[rq])
followed by a conditional expression
.IR cond-expr ;
the remainder of the line,
.IR anything ,
is interpreted as if it were an input line.
.
Any quantity of spaces between arguments to requests serves only to
separate them;
leading spaces in
.I anything
are therefore not seen.
.
.I anything
effectively
.I cannot
be omitted;
if
.I cond-expr
is true and
.I anything
is empty,
the newline at the end of the control line is interpreted as a blank
line
(and therefore a blank text line).
.
.
.P
It is frequently desirable for a control structure to govern more than
one request,
macro call,
or text line,
or a combination of the foregoing.
.
The opening and closing brace escape sequences
.esc {
and
.esc }
perform such grouping.
.
Brace escape sequences outside of control structures have no meaning and
produce no output.
.
.
.P
.esc {
should appear
(after optional spaces and tabs)
immediately subsequent to the request's conditional expression.
.
.esc }
should appear on a line with other occurrences of itself as necessary to
match
.esc {
sequences.
.
It can be preceded by a control character,
spaces,
and tabs.
.
Input after any quantity of
.esc }
sequences on the same line is processed only if all the preceding
conditions to which they correspond are true.
.
Furthermore,
a
.esc }
closing the body of a
.request .while
request must be the last such escape sequence on an input line.
.
.
.\" ====================================================================
.SS "Conditional expressions"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Operators in
.\" Conditionals".
The
.request .if ,
.request .ie ,
and
.request .while
requests test the truth values of numeric expressions.
.
They also support several additional Boolean operators;
the members of this expanded class are termed
.IR "conditional expressions" ;
their truth values are as shown below.
.
.
.br
.ne 3v
.P
.TS
rf(BI) lB
rB lx.
cond-expr\f[R].\|.\|.	.\|.\|.is true if.\|.\|.
_
T{
.BI \[aq] s1 \[aq] s2 \[aq]
T}	T{
.I s1
produces the same formatted output as
.IR s2 .
T}
T{
.BI c\~ g
T}	T{
a glyph
.I g
is available.
T}
T{
.BI d\~ m
T}	T{
a string,
macro,
diversion,
or request
.I m
is defined.
T}
e	T{
the current page number is even.
T}
T{
.BI F\~ f
T}	T{
a font named
.I f
is available.
T}
T{
.BI m\~ c
T}	T{
a color named
.I c
is defined.
T}
n	T{
the formatter is in
.I nroff
mode.
T}
o	T{
the current page number is odd.
T}
T{
.BI r\~ n
T}	T{
a register named
.I n
is defined.
T}
T{
.BI S\~ s
T}	T{
a font style named
.I s
is available.
T}
t	T{
the formatter is in
.I troff
mode.
T}
v	T{
n/a
(historical artifact;
always false).
T}
.TE
.
.
.br
.ne 2v
.P
If the first argument to an
.BR .if ,
.BR .ie ,
or
.B .while
request begins with a non-alphanumeric character apart from
.B !\&
(see below);
it performs an
.I output comparison test.
.
Shown first in the table above,
the
.I output comparison operator
interpolates a true value if formatting its comparands
.I s1
and
.I s2
produces the same output commands.
.
Other delimiters can be used in place of the neutral apostrophes.
.
.I @g@troff
formats
.I s1
and
.I s2
in separate environments;
after the comparison,
the resulting data are discarded.
.
The resulting glyph properties,
including font family,
style,
size,
and
slant,
must match,
but not necessarily the requests and/or escape sequences used to obtain
them.
.
Motions must match in orientation and magnitude to within the applicable
horizontal or vertical motion quantum of the device,
after rounding.
.
.\" TODO: Uncomment and add forward reference when we add a "GNU troff
.\" internals" subsection to this page.
.\"(All of this is to say that the lists of output nodes created by
.\"formatting
.\".I s1
.\"and
.\".I s2
.\"must be identical.)
.
.
.P
Surround the comparands with
.B \[rs]?\&
to avoid formatting them;
this causes them to be compared character by character,
as with string comparisons in other programming languages.
.
Since comparands protected with
.B \[rs]?\&
are read in copy mode,
they need not even be valid
.I groff
syntax.
.
The escape character is still lexically recognized,
however,
and consumes the next character.
.
.
.P
The above operators can't be combined with most others,
but a leading
.RB \[lq] !\& \[rq],
not followed immediately by spaces or tabs,
complements an expression.
.
Spaces and tabs are optional immediately after the
.RB \[lq] c \[rq],
.RB \[lq] d \[rq],
.RB \[lq] F \[rq],
.RB \[lq] m \[rq],
.RB \[lq] r \[rq],
and
.RB \[lq] S \[rq]
operators,
but right after
.RB \[lq] !\& \[rq],
they end the predicate and the conditional evaluates true.
.
(This bizarre behavior maintains compatibility with AT&T
.IR troff .)
.\" END Keep (roughly) parallel with groff.texi node "Operators in
.\" Conditionals".
.
.
.\" ====================================================================
.SH "Syntax reference conventions"
.\" ====================================================================
.
In the following request and escape sequence specifications,
most argument names were chosen to be descriptive.
.
A few denotations may require introduction.
.
.
.P
.LS
.RS
.
.TPx
.I c
denotes a single input character.
.
.TPx
.I font
a font either specified as a font name or a numeric mounting position.
.
.TPx
.I anything
all characters up to the end of the line,
to the ending delimiter for the escape sequence,
or within
.esc {
and
.esc } .
.
Escape sequences may generally be used freely in
.IR anything ,
except when it is read in copy mode.
.
.TPx
.I message
is a character sequence to be emitted on the standard error stream.
.
Special character escape sequences are
.I not
interpreted.
.
.TPx
.I n
is a numeric expression that evaluates to a non-negative integer.
.
.TPx
.I npl
is a numeric expression constituting a count of subsequent
.I productive
input lines;
that is,
those that directly produce formatted output.
.
Text lines produce output,
as do control lines containing requests like
.request .tl
or escape sequences like
.esc D .
.
Macro calls are not themselves productive,
but their interpolated contents can be.
.
.TPx
.I \[+-]N
is a numeric expression with a meaning dependent on its sign.
.RE
.LE
.
.
.P
If a numeric expression presented as
.I \[+-]N
starts with a
.squoted_char +
sign,
an increment in the amount of
.RI of\~ N
is applied to the value applicable to the request or escape sequence.
.
If it starts with a
.squoted_char \-
sign,
a decrement of magnitude
.I N
is applied instead.
.
Without a sign,
.I N
replaces any existing value.
.
A leading minus sign
.RI in\~ N
is always interpreted as a decrementation operator,
not an algebraic sign.
.
To assign a register a negative value or the negated value of another
register,
enclose it with its operand in
parentheses or subtract it from zero.
.
If a prior value does not exist
(the register was undefined),
an increment or decrement is applied as if to\~0.
.
.
.\" ====================================================================
.SH "Request short reference"
.\" ====================================================================
.
Not all details of request behavior are outlined here.
.
See the
.I groff
Texinfo manual or,
for features new to GNU
.IR troff , \" GNU
.MR groff_diff @MAN7EXT@ .
.
.
.P
.LS
.
.TPx
.REQ .ab
Abort processing;
exit with failure status.
.
.TPx
.REQ .ab message
Abort processing;
write
.I message
to the standard error stream and exit with failure status.
.
.
.TPx
.REQ .ad
Enable output line alignment and adjustment using the mode stored in
.BR \[rs]n[.j] .
.
.
.TPx
.REQ .ad c
Enable output line alignment and adjustment in mode
.I c
.RI ( c =\c
.BR b , c , l , n , r ).
.
Sets
.BR \[rs]n[.j] .
.
.
.TPx
.REQ .af "register c"
Assign format
.I c
to
.IR register ,
where
.I c
is
.RB \[lq] i \[rq],
.RB \[lq] I \[rq],
.RB \[lq] a \[rq],
.RB \[lq] A \[rq],
or a sequence of decimal digits whose quantity denotes the minimum width
in digits to be used when the register is interpolated.
.
.RB \[lq] i \[rq]
and
.RB \[lq] a \[rq]
indicate Roman numerals and basic Latin alphabetics,
respectively,
in the lettercase specified.
.
The default is
.BR 0 .
.
.TPx
.REQ .aln "new old"
Create alias
(additional name)
.I new
for existing register named
.IR old .
.
.TPx
.REQ .als "new old"
Create alias
(additional name)
.I new
for existing request,
string,
macro,
or diversion
.IR old .
.
.TPx
.REQ .am "macro"
Append to
.I macro
until
.B ..\&
is encountered.
.
.TPx
.REQ .am "macro end"
Append to
.I macro
until
.BI . end
is called.
.
.TPx
.REQ .am1 "macro"
Same as
.request .am
but with compatibility mode switched off during macro expansion.
.
.TPx
.REQ .am1 "macro end"
Same as
.request .am
but with compatibility mode switched off during macro expansion.
.
.TPx
.REQ .ami "macro"
Append to a macro whose name is contained in the string
.I macro
until
.B ..\&
is encountered.
.
.TPx
.REQ .ami "macro end"
Append to a macro indirectly.
.I macro
and
.I end
are strings whose contents are interpolated for the macro name and the
end macro,
respectively.
.
.TPx
.REQ .ami1 "macro"
Same as
.request .ami
but with compatibility mode switched off during macro expansion.
.
.TPx
.REQ .ami1 "macro end"
Same as
.request .ami
but with compatibility mode switched off during macro expansion.
.
.TPx
.REQ .as name
Create string
.I name
with empty contents;
no operation if
.I name
already exists.
.
.TPx
.REQ .as "name contents"
Append
.I contents
to string
.IR name .
.
.TPx
.REQ .as1 string
.TQ
.REQ .as1 "string contents"
As
.request .as ,
but with compatibility mode disabled when
.I contents
interpolated.
.
.TPx
.REQ .asciify "diversion"
Unformat ASCII characters, spaces, and some escape sequences in
.IR diversion .
.
.TPx
.REQ .backtrace
Write the state of the input stack to the standard error stream.
.
See the
.B \-b
option of
.MR groff @MAN1EXT@ .
.
.TPx
.REQ .bd font
Stop emboldening font
.I font.
.
.TPx
.REQ .bd "font n"
Embolden
.I font
by overstriking its glyphs offset by
.IR n \-1
units.
.
See
.register .b .
.\" XXX: negative values accepted; check AT&T troff
.
.TPx
.REQ .bd "special-font font"
Stop emboldening
.I special-font
when
.I font
is selected.
.
.TPx
.REQ .bd "special-font font n"
Embolden
.I special-font,
overstriking its glyphs offset by
.IR n \-1
units when
.I font
is selected.
.
See
.register .b .
.
.TPx
.REQ .blm
Unset blank line macro (trap).
.
Restore default handling of blank lines.
.
.
.TPx
.REQ .blm name
Set blank line macro (trap) to
.IR name .
.
.
.TPx
.REQ .box
Stop directing output to current diversion;
any pending output line is discarded.
.
.
.TPx
.REQ .box name
Direct output to diversion
.IR name ,
omitting a partially collected line.
.
.
.TPx
.REQ .boxa
Stop appending output to current diversion;
any pending output line is discarded.
.
.
.TPx
.REQ .boxa name
Append output to diversion
.IR name ,
omitting a partially collected line.
.
.
.TPx
.REQ .bp
Break page and start a new one.
.
.TPx
.REQ .bp "\[+-]N"
Break page,
starting a new one numbered
.IR \[+-]N .
.
.TPx
.REQ .br
Break output line.
.
.TPx
.REQ .brp
Break output line;
adjust if applicable.
.
.TPx
.REQ .break
Break out of a while loop.
.
.TPx
.REQ .c2
Reset no-break control character to
.dquoted_char \[aq] .
.
.TPx
.REQ .c2 "o"
Recognize ordinary character
.I o
as no-break control character.
.
.TPx
.REQ .cc
Reset control character to
.squoted_char . .
.
.TPx
.REQ .cc "o"
Recognize ordinary character
.I o
as the control character.
.
.TPx
.REQ .ce
Break,
center the output of the next productive input line without filling,
and break again.
.
.TPx
.REQ .ce npl
Break,
center the output of the next
.I npl
productive input lines without filling,
then break again.
.
If
.I npl
\[<=] 0,
stop centering.
.
.TPx
.REQ .cf file
Copy contents of
.I file
without formatting to the (top-level) diversion.
.
.TPx
.REQ .cflags "n c1 c2 \fR\&.\|.\|.\&\fP"
Assign properties encoded
.RI by\~ n
to characters
.IR c1 ,
.IR c2 ,
and so on.
.
.
.TPx
.REQ .ch name
Unplant page location trap
.IR name .
.
.
.TPx
.REQ .ch "name vpos"
Change page location trap
.I name
planted by
.request .wh
by moving its location to
.I vpos
(default scaling unit\~\c
.scaleindicator v ).
.
.
.TPx
.REQ .char "c contents"
Define ordinary or special character
.I c
as
.IR contents .
.
.TPx
.REQ .chop object
Remove the last character from the macro,
string,
or diversion
named
.IR object .
.
.TPx
.REQ .class "name c1 c2 \fR\&.\|.\|.\&\fP"
Define a (character) class
.I name
comprising the characters or range expressions
.IR c1 ,
.IR c2 ,
and so on.
.
.TPx
.REQ .close "stream"
Close the
.IR stream .
.
.
.TPx
.REQ .color
Enable output of color-related device-independent output commands.
.
.
.TPx
.REQ .color n
If
.I n
is zero,
disable output of color-related device-independent output commands;
otherwise,
enable them.
.\" XXX: Should probably interpret negative values as false.
.
.
.TPx
.REQ .composite "from to"
Map glyph name
.I from
to glyph name
.I to
while constructing a composite glyph name.
.
.TPx
.REQ .continue
Finish the current iteration of a while loop.
.
.TPx
.REQ .cp
Enable compatibility mode.
.
.TPx
.REQ .cp n
If
.I n
is zero,
disable compatibility mode,
otherwise enable it.
.
.TPx
.REQ .cs "font n m"
Set constant character width mode for
.I font
to
.IR n /36
ems with em
.IR m .
.\" XXX: m parameter needs more explanation.
.
.
.TPx
.REQ .cu
Continuously underline the output of the next productive input line.
.
.
.TPx
.REQ .cu npl
Continuously underline the output of the next
.I npl
productive input lines.
.
If
.IR npl =0,
stop continuously underlining.
.
.
.TPx
.REQ .da
Stop appending output to current diversion.
.
.
.TPx
.REQ .da name
Append output to diversion
.IR name .
.
.
.TPx
.REQ .de macro
Define or redefine
.I macro
until
.RB \[lq] ..\& \[rq]
occurs at the start of a control line in the current conditional block.
.
.
.TPx
.REQ .de "macro end"
Define or redefine
.I macro
until
.I end
is invoked or called at the start of a control line in the current
conditional block.
.
.
.TPx
.REQ .de1 "macro"
As
.request .de ,
but disable compatibility mode during macro expansion.
.
.TPx
.REQ .de1 "macro end"
As
.RB \[lq] .de
.IR "macro end" \[rq],
but disable compatibility mode during macro expansion.
.
.
.TPx
.REQ .defcolor "ident scheme color-component \f[R].\|.\|."
Define a color named
.I ident.
.
.I scheme
identifies a color space and determines the number of required
.IR color-component s;
it must be one of
.RB \[lq] rgb \[rq]
(three components),
.RB \[lq] cmy \[rq]
(three),
.RB \[lq] cmyk \[rq]
(four),
or
.RB \[lq] gray \[rq]
(one).
.
.RB \[lq] grey \[rq]
is accepted as a synonym of
.RB \[lq] gray \[rq].
.
The color components can be encoded as a single hexadecimal value
starting with
.B #
or
.BR ## .
.
The former indicates that each component is in the range 0\[en]255
(0\[en]FF),
the latter the range 0\[en]65,535 (0\[en]FFFF).
.
Alternatively,
each color component can be specified as a decimal fraction in the range
0\[en]1,
interpreted using a default scaling unit
.RB of\~\[lq] f \[rq],
which multiplies its value by 65,536
(but clamps it at 65,535).
.
Each output device has a color named
.RB \[lq] default \[rq],
which cannot be redefined.
.
A device's default stroke and fill colors are not necessarily the same.
.
.
.TPx
.REQ .dei "macro"
Define macro indirectly.
.
As
.request .de ,
but use interpolation of string
.I macro
as the name of the defined macro.
.
.
.TPx
.REQ .dei "macro end"
Define macro indirectly.
.
As
.request .de ,
but use interpolations of strings
.I macro
and
.I end
as the names of the defined and end macros.
.
.
.TPx
.REQ .dei1 "macro"
As
.request .dei ,
but disable compatibility mode during macro expansion.
.
.
.TPx
.REQ .dei1 "macro end"
As
.request ".dei\~\f[I]macro\~end\f[]" ,
but disable compatibility mode during macro expansion.
.
.TPx
.REQ .device "anything"
Write
.IR anything ,
read in copy mode,
to
.I @g@troff
output as a device control command.
.
An initial neutral double quote is stripped to allow embedding of
leading spaces.
.
.TPx
.REQ .devicem "name"
Write contents of macro or string
.I name
to
.I @g@troff
output as a device control command.
.
.TPx
.REQ .di
Stop directing output to current diversion.
.
.
.TPx
.REQ .di name
Direct output to diversion
.IR name .
.
.TPx
.REQ .do "name \fR\&.\|.\|.\&\fP"
Interpret the string,
request,
diversion,
or macro
.I name
(along with any arguments)
with compatibility mode disabled.
.
Compatibility mode is restored
(only if it was active)
when the
.I expansion
of
.I name
is interpreted.
.
.TPx
.REQ .ds name
Create empty string
.IR name .
.
.TPx
.REQ .ds "name contents"
Create a string
.I name
containing
.IR contents .
.
.TPx
.REQ .ds1 name
.TQ
.REQ .ds1 "name contents"
As
.request .ds ,
but with compatibility mode disabled when
.I contents
interpolated.
.
.TPx
.REQ .dt
Clear diversion trap.
.
.
.TPx
.REQ .dt "vertical-position name"
Set the diversion trap to macro
.I name
at
.I vertical-position
(default scaling unit\~\c
.scaleindicator v ).
.
.
.TPx
.REQ .ec
Recognize
.B \[rs]
as the escape character.
.
.
.TPx
.REQ .ec "o"
Recognize ordinary character
.I o
as the escape character.
.
.
.TPx
.REQ .ecr
Restore escape character saved with
.request .ecs .
.
.
.TPx
.REQ .ecs
Save the escape character.
.
.
.TPx
.REQ .el "anything"
Interpret
.I anything
as if it were an input line if the conditional expression of the
corresponding
.request .ie
request was false.
.
.
.TPx
.REQ .em name
Call macro
.I name
after the end of input.
.
.
.TPx
.REQ .eo
Disable the escape mechanism in interpretation mode.
.
.
.TPx
.REQ .ev
Pop environment stack,
returning to previous one.
.
.
.TPx
.REQ .ev "env"
Push current environment onto stack and switch to
.IR env .
.
.
.TPx
.REQ .evc "env"
Copy environment
.I env
to the current one.
.
.
.TPx
.REQ .ex
Exit with successful status.
.
.
.TPx
.REQ .fam
Set default font family to previous value.
.
.TPx
.REQ .fam "name"
Set default font family to
.IR name .
.
.TPx
.REQ .fc
Disable field mechanism.
.
.TPx
.REQ .fc "a"
Set field delimiter to\~\c
.I a
and pad glyph to space.
.
.TPx
.REQ .fc "a b"
Set field delimiter to\~\c
.I a
and pad glyph to\~\c
.IR b .
.
.TPx
.REQ .fchar "c contents"
Define fallback character (or glyph)
.I c
as
.IR contents .
.
.
.TPx
.REQ .fcolor
Restore previous fill color.
.
.
.TPx
.REQ .fcolor "c"
Set fill color to
.IR c .
.
.
.TPx
.REQ .fi
Enable filling of output lines;
a pending output line is broken.
.
Sets
.BR \[rs]n[.u] .
.
.
.TPx
.REQ .fl
Flush output buffer.
.
.TPx
.REQ .fp "pos id"
Mount font with font description file name
.I id
at non-negative
.RI position\~ n .
.
.TPx
.REQ .fp "pos id font-description-file-name"
Mount font with
.I font-description-file-name
as name
.I id
at non-negative
.RI position\~ n .
.
.TPx
.REQ .fschar "f c anything"
Define fallback character (or glyph)
.I c
for font
.I f
as string
.IR anything .
.
.TPx
.REQ .fspecial "font"
Reset list of special fonts for
.I font
to be empty.
.
.TPx
.REQ .fspecial "font s1 s2 \fR\&.\|.\|.\&\fP"
When the current font is
.IR font ,
then the fonts
.IR s1 ,
.IR s2 ,
\&.\|.\|.\&
are special.
.
.TPx
.REQ .ft
.TQ
.REQ ".ft P"
Select previous font mounting position
(abstract style or font);
same as
.esc f[]
or
.esc fP .
.
.TPx
.REQ .ft "font"
Select typeface
.I font,
which can be a
mounting position,
abstract style,
or font name;
same as
.esc[] f font
escape sequence.
.
.I font
cannot be
.BR P .
.
.TPx
.REQ .ftr "font1 font2"
Translate
.I font1
to
.IR font2 .
.
.TPx
.REQ .fzoom font
.TQ
.REQ .fzoom font\~\f[CB]0\f[]
Stop magnifying
.IR font .
.
.TPx
.REQ .fzoom "font z"
Set zoom factor for
.I font
.RI to\~ z
(in thousandths;
default:
1000).
.
.TPx
.REQ .gcolor
Restore previous stroke color.
.
.
.TPx
.REQ .gcolor "c"
Set stroke color to
.IR c .
.
.
.TPx
.REQ .hc
Reset the hyphenation character
.RB to\~ \[rs]%
(the default).
.
.TPx
.REQ .hc char
Change the hyphenation character
.RI to\~ char .
.
.TPx
.REQ .hcode "c1 code1 \fR[\fPc2 code2\fR] .\|.\|.\fP"
Set the hyphenation code of character
.I c1
to
.IR code1 ,
that of
.I c2
to
.IR code2 ,
and so on.
.
.TPx
.REQ .hla lang
Set the hyphenation language to
.IR lang .
.
.TPx
.REQ .hlm n
Set the maximum quantity of consecutive hyphenated lines to
.IR n .
.
.TPx
.REQ .hpf pattern-file
Read hyphenation patterns from
.IR pattern-file .
.
.TPx
.REQ .hpfa pattern-file
Append hyphenation patterns from
.IR pattern-file .
.
.TPx
.REQ .hpfcode "a b \fR[\fPc d\fR] .\|.\|.\fP"
Define mappings for character codes in hyphenation pattern files read
with
.request .hpf
and
.request .hpfa .
.
.TPx
.REQ .hw "word \fR.\|.\|.\fP"
Define hyphenation overrides for each
.I word;
a hyphen
.RB \[lq] \- \[rq]
indicates a hyphenation point.
.
.
.TPx
.REQ .hy
Set automatic hyphenation mode to
.BR 1 .
.
.
.TPx
.REQ .hy\~0
Disable automatic hyphenation;
same as
.BR .nh .
.
.
.TPx
.REQ .hy mode
Set automatic hyphenation mode to
.IR mode ;
see section \[lq]Hyphenation\[rq] below.
.
.
.TPx
.REQ .hym
Set the (right) hyphenation margin to
.B 0
(the default).
.
.TPx
.REQ .hym length
Set the (right) hyphenation margin to
.I length
(default scaling unit\~\c
.scaleindicator m ).
.
.TPx
.REQ .hys
Set the hyphenation space to
.B 0
(the default).
.
.TPx
.REQ .hys hyphenation-space
Suppress automatic hyphenation in adjustment modes
.RB \[lq] b \[rq]
or
.RB \[lq] n \[rq]
if the line can be justified with the addition of up to
.I hyphenation-space
to each inter-word space
(default scaling unit\~\c
.scaleindicator m ).
.
.
.TPx
.REQ .ie "cond-expr anything"
If
.I cond-expr
is true,
interpret
.I anything
as if it were an input line,
otherwise skip to a corresponding
.request .el
request.
.
.
.TPx
.REQ .if "cond-expr anything"
If
.I cond-expr
is true,
then interpret
.I anything
as if it were an input line.
.
.
.TPx
.REQ .ig
Ignore input
(except for side effects of
.B \[rs]R
on auto-incrementing registers)
until
.RB \[lq] ..\& \[rq]
occurs at the start of a control line in the current conditional block.
.
.
.TPx
.REQ .ig "end"
Ignore input
(except for side effects of
.B \[rs]R
on auto-incrementing registers)
until
.BI . end
is called at the start of a control line in the current conditional
block.
.
.TPx
.REQ .in
Set indentation amount to previous value.
.
.TPx
.REQ .in "\[+-]N"
Set indentation to
.I \[+-]N
(default scaling unit\~\c
.scaleindicator m ).
.
.TPx
.REQ .it
Cancel any pending input line trap.
.
.TPx
.REQ .it "npl name"
Set
(or replace)
an input line trap in the environment,
calling macro
.IR name ,
after the next
.I npl
productive input lines have been read.
.
Lines interrupted with the
.B \[rs]c
escape sequence are counted separately.
.
.TPx
.REQ .itc
Cancel any pending input line trap.
.
.TPx
.REQ .itc "npl name"
As
.request .it ,
except that input lines interrupted with the
.B \[rs]c
escape sequence are not counted.
.
.TPx
.REQ .kern
Enable pairwise kerning.
.
.TPx
.REQ .kern n
If
.I n
is zero,
disable pairwise kerning,
otherwise enable it.
.
.TPx
.REQ .lc
Unset leader repetition character.
.
.TPx
.REQ .lc "c"
Set leader repetition character
.RI to\~ c
(default:
.RB \[lq] . \[rq]).
.
.TPx
.REQ .length "reg anything"
Compute the number of characters of
.I anything
and store the count
in the register
.IR reg .
.
.
.TPx
.REQ .linetabs
Enable line-tabs mode
(calculate tab positions relative to beginning of output line).
.
.
.TPx
.REQ .linetabs\~0
Disable line-tabs mode.
.
.
.TPx
.REQ .lf n
Set number of next input line to
.IR n .
.\" XXX: negative values accepted; check AT&T troff
.
.TPx
.REQ .lf "n file"
Set number of next input line to
.I n
and input file name to
.IR file .
.
.TPx
.REQ .lg m
Set ligature mode to
.I m
.RB ( 0
= disable,
.B 1
= enable,
.B 2
= enable for two-letter ligatures only).
.\" XXX: negative values accepted (mapped to 1); check AT&T troff
.
.TPx
.REQ .ll
Set line length to previous value.
.
Does not affect a pending output line.
.
.TPx
.REQ .ll "\[+-]N"
Set line length to
.I \[+-]N
(default length
.scalednumber 6.5 i ,
default scaling unit\~\c
.scaleindicator m ).
.
Does not affect a pending output line.
.
.TPx
.REQ .lsm
Unset the leading space macro (trap).
.
Restore default handling of lines with leading spaces.
.
.TPx
.REQ .lsm name
Set the leading space macro (trap) to
.IR name .
.
.TPx
.REQ .ls
Change to the previous value of additional intra-line skip.
.
.TPx
.REQ .ls n
Set additional intra-line skip value to
.IR n ,
i.e.,
.IR n \-1
blank lines are inserted after each text output line.
.\" XXX: negative values accepted; check AT&T troff
.
.TPx
.REQ .lt
Set length of title lines to previous value.
.
.TPx
.REQ .lt "\[+-]N"
Set length of title lines
(default length
.scalednumber 6.5 i ,
default scaling unit\~\c
.scaleindicator m ).
.
.TPx
.REQ .mc
Cease writing margin character.
.
.TPx
.REQ .mc c
Begin writing margin
.RI character\~ c
to the right of each output line.
.
.TPx
.REQ .mc "c d"
Begin writing margin
.RI character\~ c
on each output line at
.RI distance\~ d
to the right of the right margin
(default distance
.scalednumber 10 p ,
default scaling unit\~\c
.scaleindicator m ).
.
.TPx
.REQ .mk
Mark vertical drawing position in an internal register;
see
.BR .rt .
.
.TPx
.REQ .mk register
Mark vertical drawing position in
.IR register .
.
.TPx
.REQ .mso "file"
As
.request .so ,
except that
.I file
is sought in the
.I tmac
directories.
.
.
.TPx
.REQ .msoquiet "file"
As
.request .mso ,
but no warning is emitted if
.I file
does not exist.
.
.
.TPx
.REQ .na
Disable output line adjustment.
.
.
.TPx
.REQ .ne
Break page if distance to next page location trap is less than one vee.
.
.TPx
.REQ .ne d
Break page if distance to next page location trap is less than distance
.I d
(default scaling unit\~\c
.scaleindicator v ).
.
.
.TPx
.REQ .nf
Disable filling of output lines;
a pending output line is broken.
.
Clears
.BR \[rs]n[.u] .
.
.
.TPx
.REQ .nh
Disable automatic hyphenation;
same as
.RB \[lq] ".hy 0" \[rq].
.
.TPx
.REQ .nm
Deactivate output line numbering.
.
.TPx
.REQ .nm \[+-]N
.TQ
.REQ .nm "\[+-]N m"
.TQ
.REQ .nm "\[+-]N m s"
.TQ
.REQ .nm "\[+-]N m s i"
Activate output line numbering:
number the next output line
.I \[+-]N,
writing numbers every
.I m
lines,
with
.I s
numeral widths
.RB ( \[rs]0 )
between the line number and the output
(default 1),
and indenting the line number by
.I i
numeral widths
(default 0).
.
.TPx
.REQ .nn
Suppress numbering of the next output line to be numbered with
.BR nm .
.
.TPx
.REQ .nn n
Suppress numbering of the next
.I n
output lines to be numbered with
.BR nm .
.
If
.IR n =0,
cancel suppression.
.\" XXX: negative values accepted; check AT&T troff
.
.
.TPx
.REQ .nop "anything"
Interpret
.I anything
as if it were an input line.
.
.TPx
.REQ .nr "reg \[+-]N"
Define or update register
.I reg
with value
.IR N .
.
.TPx
.REQ .nr "reg \[+-]N I"
Define or update register
.I reg
with value
.I N
and auto-increment
.IR I .
.
.TPx
.REQ .nroff
Make the conditional expressions
.B n
true and
.B t
false.
.
.TPx
.REQ .ns
Enable
.IR "no-space mode" ,
ignoring
.B .sp
requests until a glyph or
.B \[rs]D
primitive is output.
.
See
.BR .rs .
.
.TPx
.REQ .nx
Immediately jump to end of current file.
.
.TPx
.REQ .nx file
Stop formatting current file and begin reading
.I file.
.
.TPx
.REQ .open "stream file"
Open
.I file
for writing and associate the stream named
.I stream
with it.
.
Unsafe request;
disabled by default.
.
.TPx
.REQ .opena "stream file"
As
.request .open ,
but append to
.I file.
.
Unsafe request;
disabled by default.
.
.TPx
.REQ .os
Output vertical distance that was saved by the
.request .sv
request.
.
.TPx
.REQ .output contents
Emit
.I contents
directly to intermediate output,
allowing leading whitespace if
.I string
starts with
\&\f[CB]\[dq]\f[]
(which is stripped off).
.
.TPx
.REQ .pc
Reset page number character to\~\c
.squoted_char % .
.
.TPx
.REQ .pc "c"
Page number character.
.
.
.TPx
.REQ .pev
Report the state of the current environment followed by that of all
other environments to the standard error stream.
.
.TPx
.REQ .pi "program"
Pipe output to
.I program
.RI ( nroff
only).
.
Unsafe request;
disabled by default.
.
.TPx
.REQ .pl
Set page length to default
.scalednumber 11 i .
The current page length is stored in register
.BR .p .
.
.TPx
.REQ .pl "\[+-]N"
Change page length to
.I \[+-]N
(default scaling unit\~\c
.scaleindicator v ).
.
.TPx
.REQ .pm
Report,
to the standard error stream,
the names and sizes in bytes of
defined
macros,
strings,
and
diversions.
.
.TPx
.REQ .pn "\[+-]N"
Next page number
.IR N .
.
.TPx
.REQ .pnr
Write the names and contents of all defined registers to the standard
error stream.
.
.TPx
.REQ .po
Change to previous page offset.
.
The current page offset is available in register
.BR .o .
.
.TPx
.REQ .po "\[+-]N"
Page offset
.IR N .
.
.
.TPx
.REQ .ps
Return to previous type size.
.TPx
.
.
.REQ .ps "\[+-]N"
Set/increase/decrease the type size to/by
.I N
scaled points
(a non-positive resulting type size is set to 1\~u);
also see
.esc[] s \[+-]N .
.
.TPx
.REQ .psbb file
Retrieve the bounding box of the PostScript image found in
.I file,
which must conform to Adobe's Document Structuring Conventions (DSC).
.
See registers
.BR llx ,
.BR lly ,
.BR urx ,
.BR ury .
.
.TPx
.REQ .pso "command-line"
Execute
.I command-line
with
.MR popen 3
and interpolate its output.
.
Unsafe request;
disabled by default.
.
.TPx
.REQ .ptr
Report names and positions of all page location traps to the standard
error stream.
.
.
.TPx
.REQ .pvs
Change to previous post-vertical line spacing.
.
.TPx
.REQ .pvs "\[+-]N"
Change post-vertical line spacing according to
.I \[+-]N
(default scaling unit\~\c
.scaleindicator p ).
.
.TPx
.REQ .rchar "c1 c2 \fR.\|.\|.\&\fP"
Remove definition of each ordinary or special character
.IR c1 ,
.IR c2 ,
\&.\|.\|.\& defined by a
.request .char ,
.request .fchar ,
or
.request .schar
request.
.
.TPx
.REQ .rd "prompt"
Read insertion.
.
.TPx
.REQ .return
Return from a macro.
.
.TPx
.REQ .return "anything"
Return twice, namely from the macro at the current level and from the
macro one level higher.
.
.TPx
.REQ .rfschar "f c1 c2 \fR\&.\|.\|.\&\fP"
Remove the font-specific definitions of glyphs
.IR c1 ,
.IR c2 ,
\&.\|.\|.\& for
.RI font\~ f .
.
.TPx
.REQ .rj npl
Break,
right-align the output of the next productive input line without
filling,
then break again.
.
.TPx
.REQ .rj npl
Break,
right-align the output of the next
.I npl
productive input lines without filling,
then break again.
.
If
.I npl
\[<=] 0,
stop right-aligning.
.
.TPx
.REQ .rm "name"
Remove request, macro, diversion, or string
.IR name .
.
.TPx
.REQ .rn "old new"
Rename request, macro, diversion, or string
.I old
to
.IR new .
.
.TPx
.REQ .rnn "reg1 reg2"
Rename register
.I reg1
to
.IR reg2 .
.
.
.TPx
.REQ .rr ident
Remove register
.IR ident .
.
.
.TPx
.REQ .rs
Restore spacing;
disable no-space mode.
.
See
.BR .ns .
.
.TPx
.REQ .rt
Return
.I (upward only)
to vertical position marked by
.B .mk
on the current page.
.
.TPx
.REQ .rt N
Return
.I (upward only)
to vertical position
.I N
(default scaling
unit\~\c
.scaleindicator v ).
.\" XXX: negative values accepted; check AT&T troff
.
.TPx
.REQ .schar "c contents"
Define global fallback character (or glyph)\~\c
.I c
as
.IR contents .
.
.
.TPx
.REQ .shc
Reset the soft hyphen character to
.esc [hy] .
.
.
.TPx
.REQ .shc c
Set the soft hyphen character
.RI to\~ c .
.
.
.TPx
.REQ .shift n
In a macro definition,
left-shift arguments by
.IR n \~\c
positions.
.
.TPx
.REQ .sizes "s1 s2 \f[R].\|.\|.\&\f[] sn \f[R][\f[CB]0\f[]]"
Set available type sizes similarly to the
.B sizes
directive in a
.I DESC
file.
.
Each
.IR s i
is interpreted in units of scaled points (\c
.scaleindicator z ).
.
.
.TPx
.REQ .so file
Replace the request's control line with the contents of
.IR file ,
\[lq]sourcing\[rq] it.
.
.
.TPx
.REQ .soquiet file
As
.request .so ,
but no warning is emitted if
.I file
does not exist.
.
.
.TPx
.REQ .sp
Break and move the next text baseline down by one vee,
or until springing a page location trap.
.
.
.TPx
.REQ .sp dist
Break and move the next text baseline down by
.IR dist ,
or until springing a page location trap
(default scaling unit\~\c
.scaleindicator v ).
.
A negative
.I dist
will not reduce the position of the text baseline below zero.
.
Prefixing
.I dist
with the
.B \[or]
operator moves to a position relative to the page top for positive
.IR N ,
and the bottom if
.I N
is negative;
in all cases,
one line height (vee) is added
.RI to\~ dist .
.
.I dist
is ignored inside a diversion.
.
.
.TPx
.REQ .special
Reset global list of special fonts to be empty.
.
.TPx
.REQ .special "s1 s2 \fR\&.\|.\|.\&\fR"
Fonts
.IR s1 ,
.IR s2 ,
etc.\& are special and are searched for glyphs not in the
current font.
.
.TPx
.REQ .spreadwarn
Toggle the spread warning on and off (the default) without changing its
value.
.
.TPx
.REQ .spreadwarn N
Emit a
.B break
warning if the additional space inserted for each space between words in
an adjusted output line is greater than or equal to
.IR N .
.
A negative
.I N
is treated as 0.
.
The default scaling unit is\~\c
.scaleindicator m .
.
At startup,
.request .spreadwarn
is inactive and
.I N
is
.scalednumber "3 m" .
.\" XXX: negative values accepted; retain for future space-squeezing
.
.TPx
.REQ .ss n
Set minimal inter-word spacing to
.IR n \~12ths
of current font's space width.
.
.TPx
.REQ .ss "n m"
As
.RB \[lq] .ss\~\c
.IR n \[rq],
and set additional inter-sentence space to
.IR m \~12ths
of current font's space width.
.
.TPx
.REQ .stringdown stringvar
Replace each byte in the string named
.I stringvar
with its lowercase version.
.
.TPx
.REQ .stringup stringvar
Replace each byte in the string named
.I stringvar
with its uppercase version.
.
.TPx
.REQ .sty "n style"
Associate abstract
.I style
with font position
.IR n .
.
.TPx
.REQ .substring "str start \fR[\fPend\fR]\fP"
Replace the string named
.I str
with its substring bounded by the indices
.I start
and
.IR end ,
inclusive.
.
Negative indices count backwards from the end of the string.
.
.TPx
.REQ .sv
As
.request .ne ,
but save
.scalednumber "1 v"
for output with
.request .os
request.
.
.TPx
.REQ .sv d
As
.request .ne ,
but save distance
.I d
for later output with
.request .os
request
(default scaling unit\~\c
.scaleindicator v ).
.\" XXX: negative values accepted; check AT&T troff
.
.TPx
.REQ .sy "command-line"
Execute
.I command-line
with
.MR system 3 .
.
Unsafe request;
disabled by default.
.
.TPx
.REQ .ta "n1 n2 \fR\&.\|.\|.\&\fP n\fRn\fP \f[CB]T\f[] r1 r2 \
\fR\&.\|.\|.\&\fP r\fRn\fP"
Set tabs at positions
.IR n1 ,
.IR n2 ,
\&.\|.\|.\&,
.IR n n,
then set tabs at
.IR n n+ m \[tmu] r n+ r1
through
.IR n n+ m \[tmu] r n+ r n,
where
.I m
increments from 0,
1,
2,
\&.\|.\|.\& to the output line length.
.
Each
.IR n \~argument
can be prefixed with
.RB a\~\[lq] + \[rq]
to place the tab stop
.I ni
at a distance relative to the previous,
.IR n ( i \-1).
.
Each argument
.IR ni \~or\~ ri
can be suffixed with a letter to align text within the tab column
bounded by tab stops
.IR i \~and\~ i +1;
.RB \[lq] L \[rq]
for left-aligned
(the default),
.RB \[lq] C \[rq]
for centered,
and
.RB \[lq] R \[rq]
for right-aligned.
.
.br
.ne 4v \" XXX: should need only 2v
.TPx
.REQ .tag
.TQ
.REQ .taga
Reserved for internal use.
.
.TPx
.REQ .tc
Unset tab repetition character.
.
.TPx
.REQ .tc "c"
Set tab repetition character
.RI to\~ c
(default: none).
.
.TPx
.REQ .ti "\[+-]N"
Temporarily indent next output line
(default scaling unit\~\c
.scaleindicator m ).
.
.TPx
.REQ .tkf "font s1 n1 s2 n2"
Enable track kerning for
.IR font .
.
.TPx
.REQ .tl "\f[CB]\[aq]\f[]left\f[CB]\[aq]\f[]center\f[CB]\[aq]\f[]right\
\f[CB]\[aq]\f[]"
Format three-part title.
.
.TPx
.REQ .tm message
Write
.I message,
followed by a newline,
to the standard error stream.
.
.TPx
.REQ .tm1 message
As
.request .tm ,
but an initial neutral double quote in
.I message
is removed,
allowing it to contain leading spaces.
.
.TPx
.REQ .tmc message
As
.request .tm1 ,
without emitting a newline.
.
.TPx
.REQ .tr "abcd\fR\&.\|.\|.\&\fP"
Translate ordinary or special characters
.I a
to
.IR b ,
.I c
to
.IR d ,
and so on prior to output.
.
.TPx
.REQ .trf file
Transparently output the contents of
.I file.
.
Unlike
.request .cf ,
invalid input characters in
.I file
are rejected.
.
.TPx
.REQ .trin "abcd\fR\&.\|.\|.\&\fP"
As
.request .tr ,
except that
.request .asciify
ignores the translation when a diversion is interpolated.
.
.TPx
.REQ .trnt "abcd\fR\&.\|.\|.\&\fP"
As
.request .tr ,
except that translations are suppressed in the argument to
.esc ! .
.
.TPx
.REQ .troff
Make the conditional expressions
.B t
true and
.B n
false.
.
.TPx
.REQ .uf font
Set underline font used by
.request .ul
to
.I font.
.
.
.TPx
.REQ .ul
Underline
(italicize in
.I troff
mode)
the output of the next productive input line.
.
.
.TPx
.REQ .ul npl
Underline
(italicize in
.I troff
mode)
the output of the next
.I npl
productive input line.
.
If
.IR npl =0,
stop underlining.
.
.
.TPx
.REQ .unformat "diversion"
Unformat space characters and tabs in
.IR diversion ,
preserving font information.
.
.
.TPx
.REQ .vpt
Enable vertical position traps.
.
.
.TPx
.REQ .vpt\~0
Disable vertical position traps.
.
.
.TPx
.REQ .vs
Change to previous vertical spacing.
.
.TPx
.REQ .vs "\[+-]N"
Set vertical spacing to
.I \[+-]N
(default scaling unit\~\c
.scaleindicator p ).
.
.
.TPx
.REQ .warn
Enable all warning categories.
.
.
.TPx
.REQ .warn\~0
Disable all warning categories.
.
.
.TPx
.REQ .warn n
Enable warnings in categories whose codes sum
.RI to\~ n ;
.\" TODO: Move that table here, perhaps.
see
.MR @g@troff @MAN1EXT@ .
.
.
.TPx
.REQ .warnscale "su"
Set scaling unit used in certain warnings \" `output_warning()`
to
.I su
(one of
.BR u ,
.BR i ,
.BR c ,
.BR p ,
or
.BR P ;
default:
.BR i ).
.
.
.TPx
.REQ .wh vpos
Remove visible page location trap at
.I vpos
(default scaling unit\~\c
.scaleindicator v ).
.
.
.TPx
.REQ .wh "vpos name"
Plant macro
.I name
as page location trap at
.I vpos
(default scaling unit\~\c
.scaleindicator v ),
removing any visible trap already there.
.
.
.TPx
.REQ .while "cond-expr anything"
Repeatedly execute
.I anything
unless and until
.I cond-expr
evaluates false.
.
.
.TPx
.REQ .write "stream anything"
Write
.I anything
to the stream named
.IR stream .
.
.TPx
.REQ .writec "stream anything"
Similar to
.request .write
without emitting a final newline.
.
.TPx
.REQ .writem "stream xx"
Write contents of macro or string
.I xx
to the stream named
.IR stream .
.
.LE
.
.
.\" ====================================================================
.SH "Escape sequence short reference"
.\" ====================================================================
.
The escape sequences
.esc \[dq] ,
.esc # ,
.esc $ ,
.esc * ,
.esc ? ,
.esc a ,
.esc e ,
.esc n ,
.esc t ,
.esc g ,
.esc V ,
and
.escarg \& newline
are interpreted even in copy mode.
.
.
.P
.LS
.
.\" ========= comments =========
.
.TP
.ESC \[dq]
Comment.
.
Everything up to the end of the line is ignored.
.
.
.TP
.ESC #
Comment.
.
Everything up to and including the next newline is ignored.
.
.
.\" ========= strings =========
.
.TP
.ESC * s
Interpolate string with one-character
.RI name\~ s .
.
.
.TP
.ESC *( st
Interpolate string with two-character
.RI name\~ st .
.
.
.TP
.ESC[] * string
Interpolate string with name
.I string
(of arbitrary length).
.
.
.TP
.ESC[] * "string arg \fR\&.\|.\|.\fP"
Interpolate string with name
.I string
(of arbitrary length),
taking
.I arg
\&.\|.\|.\&
as arguments.
.
.
.\" ========= macro arguments =========
.
.TP
.ESC $0
Interpolate name by which currently executing macro was invoked.
.
.
.TP
.ESC $ n
Interpolate macro or string parameter
.RI numbered\~ n
.RI (1\|\[<=]\| n \|\[<=]\|9).
.
.
.TP
.ESC $( nn
Interpolate macro or string parameter
.RI numbered\~ nn
.RI (01\|\[<=]\| nn \|\[<=]\|99).
.
.TP
.ESC[] $ nnn
Interpolate macro or string parameter
.RI numbered\~ nnn
.RI ( nnn \|\[>=]\|1).
.
.
.TP
.ESC $*
Interpolate concatenation of all macro or string parameters,
separated by spaces.
.
.
.TP
.ESC $@
Interpolate concatenation of all macro or string parameters,
with each surrounded by double quotes and separated by spaces.
.
.
.TP
.ESC $\[ha]
Interpolate concatenation of all macro or string parameters
as if they were arguments to the
.request .ds
request.
.
.
.\" ========= escaped characters =========
.
.
.TP
.ESC \[aq]
is a synonym for
.esc [aa] ,
the acute accent special character.
.
.
.TP
.ESC \[ga]
is a synonym for
.esc [ga] ,
the grave accent special character.
.
.
.TP
.ESC \-
is a synonym for
.esc [\-] ,
the minus sign special character.
.
.
.TP
.ESC _
is a synonym for
.esc [ul] ,
the underrule special character.
.
.
.TP
.ESC %
Control hyphenation.
.
.
.TP
.ESC !
Transparent line.
.
The remainder of the input line is interpreted
(1) when the current diversion is read;
or
(2) if in the top-level diversion,
by the postprocessor
(if any).
.
.
.TP
.ESC? anything
Transparently embed
.IR anything ,
read in copy mode,
in a diversion,
or unformatted as an output comparand in a conditional expression.
.
.
.\" ========= spaces and fixed-width horizontal motions =========
.
.TP
.ESC \f[I]space
Move right one word space.
.
.
.TP
.ESC \[ti]
Insert an unbreakable,
adjustable space.
.
.
.TP
.ESC 0
Move right by the width of a numeral in the current font.
.
.
.TP
.ESC |
Move one-sixth em to the right on typesetters.
.
.
.TP
.ESC \[ha]
Move one-twelfth em to the right on typesetters.
.
.
.TP
.ESC &
Interpolate a dummy character.
.
.
.TP
.ESC )
Interpolate a dummy character that is transparent to end-of-sentence
recognition.
.
.
.TP
.ESC /
Apply italic correction.
.
Use between an immediately adjacent oblique glyph on the left and an
upright glyph on the right.
.
.
.TP
.ESC ,
Apply left italic correction.
.
Use between an immediately adjacent upright glyph on the left and an
oblique glyph on the right.
.
.
.TP
.ESC :
Non-printing break point
(similar to
.esc % ,
but never produces a hyphen glyph).
.
.
.TP
.ESC "" newline
Continue current input line on the next.
.
.
.\" ========= structuring =========
.
.TP
.ESC {
Begin conditional input.
.
.TP
.ESC }
End conditional input.
.
.\" ========= longer escape names =========
.
.TP
.ESC ( gl
Interpolate glyph with two-character name
.IR gl .
.
.
.TP
.ESC[] "" glyph
Interpolate glyph with name
.I glyph
(of arbitrary length).
.
.
.TP
.ESC[] "" "base-char comp \fR\&.\|.\|."
Interpolate composite glyph constructed from
.I base-char
and each component
.IR comp .
.
.
.TP
.ESC[] "" "\f[CB]char\f[]nnn"
Interpolate glyph of eight-bit encoded character
.IR nnn ,
where
.RI 0\|\[<=]\| nnn \|\[<=]\|255.
.
.
.TP
.ESC[] "" "\f[CB]u\f[]nnnn\f[R][\f[]n\f[R][\f[]n\f[R]]]"
Interpolate glyph of Unicode character with code point
.IR nnnn [ n [ n ]]
in uppercase hexadecimal.
.
.
.TP
.ESC[] "" "\f[CB]u\f[]base-char\f[R][\f[]\f[CB]_\f[]\
combining-component\f[R]].\|.\|."
Interpolate composite glyph from Unicode character
.I base-char
and
.IR combining-components .
.
.
.\" ========= alphabetical escape sequences =========
.
.TP
.ESC a
Interpolate a leader in copy mode.
.
.TP
.ESCq A anything
Interpolate 1 if
.I anything
is a valid identifier,
and\~0 otherwise.
.
.TP
.ESCq b string
Build bracket:
pile a sequence of glyphs corresponding to each character in
.I string
vertically,
and center it vertically on the output line.
.
.TP
.ESCq B anything
Interpolate 1 if
.I anything
is a valid numeric expression,
and\~0 otherwise.
.
.
.TP
.ESC c
Continue output line at next input line.
.
.
.TP
.ESCq C glyph
As
.esc[] "" glyph ,
but compatible with other
.I troff \" generic
implementations.
.
.
.TP
.ESC d
Move downward \[12]\~em on typesetters.
.\" XXX: No current groff nroff-mode output driver supports half-line
.\" motions.
.\" (\[12]\~line in
.\" .I nroff
.\" contingent on device support).
.
.
.TP
.ESCq D drawing-command
See subsection \[lq]Drawing commands\[rq] below.
.
.
.TP
.ESC e
Interpolate the escape character.
.
.
.TP
.ESC E
As
.esc e ,
but not interpreted in copy mode.
.
.TP
.ESC fP
Select previous font mounting position
(abstract style or font);
same as
.RB \[lq] .ft \[rq]
or
.RB \[lq] .ft\~P \[rq].
.
.TP
.ESC f F
Select font mounting position,
abstract style,
or font with one-character name or one-digit
.RI position\~ F .
.
.IR F \~cannot
be
.BR P .
.
.TP
.ESC f( ft
Select font mounting position,
abstract style,
or font with two-character name or two-digit
.RI position\~ ft .
.
.TP
.ESC[] f font
Select font mounting position,
abstract style,
or font with arbitrarily long name or position
.IR font .
.
.I font
cannot be
.BR P .
.
.TP
.ESC[] f ""
Select previous font mounting position
(abstract style or font).
.
.TP
.ESC F f
Set default font family to that with one-character
.RI name\~ f .
.
.TP
.ESC F( fm
Set default font family to that with two-character
.RI name\~ fm .
.
.TP
.ESC[] F fam
Set default font family to that with arbitrarily long name
.IR fam .
.
.TP
.ESC[] F ""
Set default font family to previous value.
.
.TP
.ESC g r
Interpolate format of register with one-character
.RI name\~ r .
.
.
.TP
.ESC g( rg
Interpolate format of register with two-character
.RI name\~ rg .
.
.
.TP
.ESC[] g reg
Interpolate format of register with arbitrarily long name
.IR reg .
.
.
.TP
.ESCq h N
Horizontally move the drawing position by
.IR N \~ems
(or specified units);
.B \[or]
may be used.
.
Positive motion is rightward.
.
.
.TP
.ESCq H N
Set height of current font to
.IR N \~scaled
points
(or specified units).
.
.
.TP
.ESC k r
Mark horizontal position in one-character register
.RI name\~ r .
.
.TP
.ESC k( rg
Mark horizontal position in two-character register
.RI name\~ rg .
.
.
.TP
.ESC[] k reg
Mark horizontal position in register with arbitrarily long
.RI name\~ reg .
.
.
.TP
.ESCq l N\/\f[R][\f[]c\f[R]]
Draw horizontal line of length
.I N
with character
.B c
(default:
.BR \[rs][ru] ;
default scaling unit\~\c
.scaleindicator m ).
.
.
.
.TP
.ESCq L N\/\f[R][\f[]c\f[R]]
Draw vertical line of length
.I N
with character
.B c
(default:
.BR \[rs][br] ;
default scaling unit\~\c
.scaleindicator v ).
.
.
.TP
.ESC m c
Set stroke color to that with one-character
.RI name\~ c .
.
.
.TP
.ESC m( cl
Set stroke color to that with two-character
.RI name\~ cl .
.
.
.TP
.ESC[] m color
Set stroke color to that with arbitrarily long
.RI name\~ color .
.
.
.TP
.ESC[] m ""
Restore previous stroke color.
.
.
.TP
.ESC M c
Set fill color to that with one-character
.RI name\~ c .
.
.
.TP
.ESC M( cl
Set fill color to that with two-character
.RI name\~ cl .
.
.
.TP
.ESC[] M color
Set fill color to that with arbitrarily long
.RI name\~ color .
.
.
.TP
.ESC[] M ""
Restore previous fill color.
.
.
.br
.ne 4v \" XXX: why not 3v?
.TP
.ESC n r
Interpolate contents of register with one-character
.RI name\~ r .
.
.
.TP
.ESC n( rg
Interpolate contents of register with two-character
.RI name\~ rg .
.
.
.TP
.ESC[] n reg
Interpolate contents of register with arbitrarily long
.RI name\~ reg .
.
.
.TP
.ESCq N n
Interpolate glyph with
.RI index\~ n
in the current font.
.
.TP
.ESCq o abc\f[R].\|.\|.\f[]
Overstrike centered glyphs of characters
.IR a ,
.IR b ,
.IR c ,
and so on.
.
.TP
.ESC O0
At the outermost suppression level,
disable emission of glyphs and geometric objects to the output
driver.
.
.
.TP
.ESC O1
At the outermost suppression level,
enable emission of glyphs and geometric objects to the output driver.
.
.
.TP
.ESC O2
At the outermost suppression level,
enable glyph and geometric primitive emission to the output driver and
write to the standard error stream the page number,
four bounding box registers enclosing glyphs written since the previous
.B \[rs]O
escape sequence,
the page offset,
line length,
image file name
(if any),
horizontal and vertical device motion quanta,
and input file name.
.
.
.TP
.ESC O3
Begin a nested suppression level.
.
.
.TP
.ESC O4
End a nested suppression level.
.
.
.TP
.ESC[] O "\f[CB]5\f[]Pfile"
At the outermost suppression level,
write the name
.I file
to the standard error stream at
.RI position\~ P ,
which must be one of
.BR l ,
.BR r ,
.BR c ,
or
.BR i .
.
.
.TP
.ESC p
Break output line at next word boundary;
adjust if applicable.
.
.
.TP
.ESC r
Move \[lq]in reverse\[rq] (upward) 1\~em.
.
.
.TP
.ESCq R "name\~\[+-]N"
Set,
increment,
or decrement register
.I name
.RI by\~ N .
.
.
.TP
.ESC s \[+-]N
Set/increase/decrease the type size to/by
.I N
scaled points.
.
.I N
must be a single digit;
0 restores the previous type size.
.
(In compatibility mode only,
a non-zero
.I N
must be in the range 4\[en]39.)
.
Otherwise,
as
.request .ps
request.
.
.
.TP
.ESC s( \[+-]N
.TQ
.fam C
.BI \es \[+-] ( N
.fam
Set/increase/decrease the type size to/by
.I N
scaled points;
.I N
is a two-digit number \[>=]1.
.
As
.request .ps
request.
.
.
.TP
.ESC[] s \[+-]N
.TQ
.fam C
.BI \es \[+-] [ N ]
.fam
.TQ
.ESCq s \[+-]N
.TQ
.fam C
.BI \es \[+-] \[aq] N \[aq]
.fam
Set/increase/decrease the type size to/by
.I N
scaled points.
.
As
.request .ps
request.
.
.
.TP
.ESCq S N
Slant output glyphs by
.I N
degrees;
the direction of text flow is positive.
.
.
.TP
.ESC t
Interpolate a tab in copy mode.
.
.
.TP
.ESC u
Move upward \[12]\~em on typesetters.
.\" XXX: No current groff nroff-mode output driver supports half-line
.\" motions.
.\" (\[12]\~line in
.\" .I nroff
.\" contingent on device support).
.
.
.TP
.ESCq v N
Vertically move the drawing position by
.IR N \~vees
(or specified units);
.B \[or]
may be used.
.
Positive motion is downward.
.
.
.TP
.ESC V e
Interpolate contents of environment variable with one-character
.RI name\~ e .
.
.
.TP
.ESC V( ev
Interpolate contents of environment variable with two-character
.RI name\~ ev .
.
.
.TP
.ESC[] V env
Interpolate contents of environment variable with arbitrarily long
.RI name\~ env .
.
.
.TP
.ESCq w anything
Interpolate width of
.IR anything ,
formatted in a dummy environment.
.
.
.TP
.ESCq x N
Increase vertical spacing of pending output line by
.IR N \~vees
(or specified units;
negative before,
positive after).
.
.TP
.ESCq X anything
Write
.I anything
to
.I @g@troff
output as a device control command.
.
Within
.IR anything ,
the escape sequences
.BR \[rs]& ,
.BR \[rs]) ,
.BR \[rs]% ,
and
.B \[rs]:
are ignored;
.BI \[rs] space
and
.B \[rs]\[ti]
are converted to single space characters;
and
.B \[rs]\[rs]
has its escape character stripped.
.
So that the basic Latin subset of the Unicode character
set can be reliably encoded in
.I anything,
the special character escape sequences
.BR \[rs]\- ,
.BR \[rs][aq] ,
.BR \[rs][dq] ,
.BR \[rs][ga] ,
.BR \[rs][ha] ,
.BR \[rs][rs] ,
and
.B \[rs][ti]
are mapped to basic Latin characters;
see
.MR groff_char @MAN7EXT@ .
.
For this transformation,
character translations and special character definitions are ignored.
.
.TP
.ESC Y n
Write contents of macro or string
.I n
to
.I @g@troff
output as a device control command.
.
.TP
.ESC Y( nm
Write contents of macro or string
.I nm
to
.I @g@troff
output as a device control command.
.
.TP
.ESC[] Y name
Write contents of macro or string
.I name
to
.I @g@troff
output as a device control command.
.
.TP
.ESC z c
Format character
.I c
with zero width\[em]without advancing the drawing position.
.
.TP
.ESCq Z anything
Save the drawing position,
format
.IR anything ,
then restore it.
.LE
.
.
.\" ====================================================================
.SS "Drawing commands"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Drawing
.\" commands".
Drawing commands direct the output device to render geometrical objects
rather than glyphs.
.
Specific devices may support only a subset,
or may feature additional ones;
consult the man page for the output driver in use.
.
Terminal devices in particular implement almost none.
.
.
.P
Rendering starts at the drawing position;
when finished,
the drawing position is left at the rightmost point of the object,
even for closed figures,
except where noted.
.
GNU
.I troff \" GNU
draws stroked (outlined) objects with the stroke color,
and shades filled ones with the fill color.
.
See section \[lq]Colors\[rq] above.
.
Coordinates
.I h
and
.I v
are horizontal and vertical motions relative to the drawing position
or previous point in the command.
.
The default scaling unit for horizontal measurements
(and diameters of circles)
.RB is\~ m ;
for vertical ones,
.BR v .
.
.
.P
Circles,
ellipses,
and polygons can be drawn stroked or filled.
.
These are independent properties;
if you want a filled,
stroked figure,
you must draw the same figure twice using each drawing command.
.
A filled figure is always smaller than an outlined one because the
former is drawn only within its defined area,
whereas strokes have a line thickness
(set with
.BR \[rs]D\[aq]t\[aq] ).
.
.
.P
.LS
.TP
.BI \[rs]D\[aq]\[ti]\~ "h1 v1"\~\c
.RI .\|.\|.\~ "hn vn"\c
.B \[aq]
Draw B-spline to each point in sequence,
leaving drawing position at
.RI ( hn ,\~ vn ).
.
.\" XXX: This is one case where a valid coordinate pair could be off the
.\" page (even negative) and we need to discuss this frankly.
.TP
.BI \[rs]D\[aq]a\~ "hc vc h v" \[aq]
Draw circular arc centered at
.RI ( hc ,\~ vc )
counterclockwise from the drawing position to a point
.RI ( h ,\~ v )
relative to the center.
.
.RI ( hc ,\~ vc )
is adjusted to the point nearest the perpendicular bisector of the arc's
chord.
.
.TP
.BI \[rs]D\[aq]c\~ "d" \[aq]
Draw circle of diameter
.I d
with its leftmost point at the drawing position.
.
.TP
.BI \[rs]D\[aq]C\~ "d" \[aq]
As
.BR \[rs]D\[aq]C\[aq] ,
but the circle is filled.
.
.TP
.BI \[rs]D\[aq]e\~ "h v" \[aq]
Draw ellipse of width
.I h
and height
.I v
with its leftmost point at the drawing position.
.
.\" How do we draw an ellipse with rotated axes?
.TP
.BI \[rs]D\[aq]E\~ "h v" \[aq]
As
.BR \[rs]D\[aq]e\[aq] ,
but the ellipse is filled.
.
.\" XXX: Df and dF are taken care of by \M and .defcolor.
.TP
.BI \[rs]D\[aq]l\~ "h v" \[aq]
Draw line from the drawing position to
.RI ( h ,\~ v ).
.
.TP
.BI \[rs]D\[aq]p\~ "h1 v1"\~\c
.RI .\|.\|.\~ "hn vn"\c
.B \[aq]
Draw polygon with vertices at drawing position and each point
in sequence.
.
GNU
.I troff \" GNU
closes the polygon by drawing a line from
.RI ( hn ,\~ vn )
back to the initial drawing position.
.
.\" XXX: This would be the "STUPID_DRAWING_POSITIONING" complained of in
.\" src/libs/libdriver/input.cpp.  It is neither the rightmost point
.\" of the figure nor the initial drawing position that GNU troff
.\" automatically returned to to close the figure.
Afterward,
the drawing position is left at
.RI ( hn ,\~ vn ).
.
.TP
.BI \[rs]D\[aq]P\~ "h1 v1"\~\c
.RI .\|.\|.\~ "hn vn"\c
.B \[aq]
As
.BR \[rs]D\[aq]p\[aq] ,
but the polygon is filled.
.
.TP
.BI \[rs]D\[aq]t\~ "n" \[aq]
Set stroke thickness of geometric objects to
.RI to\~ n
basic units.
.
A zero
.I n
selects the minimal supported thickness.
.
A negative
.I n
selects a thickness proportional to the type size;
this is the default.
.LE
.\" END Keep (roughly) parallel with groff.texi node "Drawing
.\" commands".
.
.
.\" ====================================================================
.SS "Device control commands"
.\" ====================================================================
.
The
.B .device
and
.B .devicem
requests,
and
.B \[rs]X
and
.B \[rs]Y
escape sequences,
enable documents to pass information directly to a postprocessor.
.
These are useful for
exercising device-specific capabilities that the
.I groff
language does not abstract or generalize;
such functions include the embedding of hyperlinks and image files.
.
Device-specific functions are documented in
each output driver's man page.
.
.
.\" ====================================================================
.SH Strings
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Strings".
.I groff
supports strings primarily for user convenience.
.
Conventionally,
if one would define a macro only to interpolate a small amount of text,
without invoking requests or calling any other macros,
one defines a string instead.
.
Only one string is predefined by the language.
.
.
.TPx
.STRING .T
Contains the name of the output device
(for example,
.RB \[lq] utf8 \[rq]
or
.RB \[lq] pdf \[rq] ).
.
.
.P
The
.request .ds
request creates a string with a specified name and contents.
.
If the identifier named by
.request .ds
already exists as an alias,
the target of the alias is redefined.
.
If
.request .ds
is called with only one argument,
the named string becomes empty.
.
Otherwise,
.I @g@troff
stores the remainder of the control line in copy mode;
see subsection \[lq]Copy mode\[rq] below.
.
.
.P
The
.esc *
escape sequence dereferences a string's name,
interpolating its contents.
.
If the name does not exist,
it is defined as empty,
nothing is interpolated,
and a warning in category
.RB \%\[lq] mac \[rq]
is emitted.
.
See section \[lq]Warnings\[rq] in
.MR @g@troff 1 .
.
The bracketed interpolation form accepts arguments that are handled as
macro arguments are;
see section \[lq]Calling macros\[rq] above.
.
In contrast to macro calls,
however,
if a closing bracket
.B ]
occurs in a string argument,
that argument must be enclosed in double quotes.
.
.B \[rs]*
is interpreted even in copy mode.
.
When defining strings,
argument interpolations must be escaped if they are to reference
parameters from the calling context;
see section \[lq]Parameters\[rq] below.
.
.
.P
An initial neutral double quote
.B \[dq]
in the string contents is stripped to allow embedding of leading spaces.
.
Any other
.B \[dq]
is interpreted literally,
but it is wise to use the special character escape sequence
.B \[rs][dq]
instead if the string might be interpolated as part of a macro argument;
see section \[lq]Calling macros\[rq] above.
.
Strings are not limited to a single input line of text.
.BI \[rs] newline
works just as it does elsewhere.
.
The resulting string is stored
.I without
the newlines.
.
Care is therefore required when interpolating strings while filling is
disabled.
.
It is not possible to embed a newline in a string that will be
interpreted as such when the string is interpolated.
.
To achieve that effect,
use
.B \[rs]*
to interpolate a macro instead.\" see @ref{Punning Names}.
.
.
.P
The
.request .as
request is similar to
.request .ds
but appends to a string instead of redefining it.
.
If
.request .as
is called with only one argument,
no operation is performed
(beyond dereferencing the string).
.
.
.P
Because strings are similar to macros,
they too can be defined to suppress AT&T
.I troff \" AT&T
compatibility mode enablement when interpolated;
see section \[lq]Compatibility mode\[rq] below.
.
The
.request .ds1
request defines a string that suspends compatibility mode when the
string is later interpolated.
.
.request .as1
is likewise similar to
.BR .as ,
with compatibility mode suspended when the appended portion of the
string is later interpolated.
.
.
.P
.B Caution:
Unlike other requests,
the second argument to these requests consumes the remainder of the
input line,
including trailing spaces.
.
Ending string definitions
(and appendments)
with a comment,
even an empty one,
prevents unwanted space from creeping into them during source document
maintenance.
.
.
.br
.ne 3v
.P
Several requests exist to perform rudimentary string operations.
.
Strings can be queried
(\c
.request .length )
and modified
(\c
.request .chop ,
.request .substring ,
.request .stringup ,
.request .stringdown ),
and their names can be manipulated through renaming,
removal,
and aliasing
(\c
.request .rn ,
.request .rm ,
.request .als).
.
.
.P
When a request,
macro,
string,
or diversion is aliased,
redefinitions and appendments \[lq]write through\[rq] alias names.
.
To replace an alias with a separately defined object,
you must use the
.B rm
request on its name first.
.\" END Keep (roughly) parallel with groff.texi node "Strings".
.
.
.\" ====================================================================
.SH Registers
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Registers".
In the
.I roff
language,
numbers can be stored in
.I registers.
.
Many built-in registers exist,
supplying anything from the date to details of formatting parameters.
.
You can also define your own.
.
See section \[lq]Identifiers\[rq] above for information on constructing
a valid name for a register.
.
.
.P
Define registers and update their values with the
.B nr
request or the
.B \[rs]R
escape sequence.
.
.
.P
Registers can also be incremented or decremented by a configured amount
at the time they are interpolated.
.
The value of the increment is specified with a third argument to the
.request .nr
request,
and a special interpolation syntax,
.BI \[rs]n \[+-]
is used to alter and then retrieve
the register's value.
.
Together,
these features are called
.IR auto-increment .
.
(A negative auto-increment can be
considered an \[lq]auto-decrement\[rq].)
.
.
.P
Many predefined registers are available.
.
In the following presentation,
the register interpolation syntax
.BI \[rs]n[ name ]
is used to refer to a register
.I name
to clearly distinguish it from a string or request
.IR name .
.
The register name space is separate from that used for requests,
macros,
strings,
and diversions.
.
Bear in mind that the symbols
.B \[rs]n[]
are
.I not
part of the register name.
.\" END Keep (roughly) parallel with groff.texi node "Registers".
.
.
.\" ====================================================================
.SS "Read-only registers"
.\" ====================================================================
.
Predefined registers whose identifiers start with a dot are read-only.
.
Many are Boolean-valued.
.
Some are string-valued,
meaning that they interpolate text.
.
A register name
(without the dot)
is often associated with a request of the same name;
exceptions are noted.
.
.
.P
.LS
.
.TP 15n
.REG .$
Count of arguments passed to currently interpolated macro or string.
.
.TP
.REG .a
Amount of extra post-vertical line space;
see
.esc x .
.
.TP
.REG .A
Approximate output is being formatted (Boolean-valued);
see
.I @g@troff
.B \-a
option.
.
.TP
.REG .b
Font emboldening offset;
see
.request .bd .
.
.TP
.REG .br
The normal control character was used to call the currently interpolated
macro (Boolean-valued).
.
.TP
.REG .c
Input line number;
see
.request .lf
and
.register \f[R]\[lq]\f[]c.\f[R]\[rq]\f[] .
.
.TP
.REG .C
Compatibility mode is enabled (Boolean-valued);
see
.request .cp .
.
Always false when processing
.request .do ;
see
.register .cp .
.
.TP
.REG .cdp
Depth of last glyph formatted in the environment;
.\" TODO: Give page a discussion of glyph properties and move this.
positive if glyph extends below the baseline.
.
.TP
.REG .ce
Count of output lines remaining to be centered.
.
.TP
.REG .cht
Height of last glyph formatted in the environment;
.\" TODO: Give page a discussion of glyph properties and move this.
positive if glyph extends above the baseline.
.
.TP
.REG .color
Color output is enabled (Boolean-valued).
.
.TP
.REG .cp
Within
.request .do ,
the saved value of compatibility mode;
see
.register .C .
.
.TP
.REG .csk
Skew of the last glyph formatted in the environment;
.\" TODO: Give page a discussion of glyph properties and move this.
skew is how far to the right of the center of a glyph the center of an
accent over that glyph should be placed.
.
.TP
.REG .d
Vertical drawing position in diversion.
.
.TP
.REG .ev
Name of environment (string-valued).
.
.TP
.REG .f
Mounting position of selected font;
see
.request .ft
and
.esc f .
.
.TP
.REG .F
Name of input file (string-valued);
see
.request .lf .
.
.TP
.REG .fam
Name of default font family (string-valued).
.
.TP
.REG .fn
Resolved name of selected font (string-valued);
see
.request .ft
and
.esc f .
.
.TP
.REG .fp
Next non-zero free font mounting position index.
.
.TP
.REG .g
Always true in GNU
.I troff \" GNU
(Boolean-valued).
.
.TP
.REG .h
Text baseline high-water mark on page or in diversion.
.
.TP
.REG .H
Horizontal motion quantum of output device in basic units.
.
.TP
.REG .height
Font height;
see
.esc H .
.
.TP
.REG .hla
Hyphenation language in environment (string-valued).
.
.TP
.REG .hlc
Count of immediately preceding consecutive hyphenated lines in
environment.
.
.TP
.REG .hlm
Maximum quantity of consecutive hyphenated lines allowed in environment.
.
.TP
.REG .hy
Automatic hyphenation mode in environment.
.
.TP
.REG .hym
Hyphenation margin in environment.
.
.TP
.REG .hys
Hyphenation space adjustment threshold in environment.
.
.TP
.REG .i
Indentation amount;
see
.request .in .
.
.TP
.REG .in
Indentation amount applicable to the pending output line;
see
.request .ti .
.
.TP
.REG .int
Previous output line was \[lq]interrupted\[rq] or continued with
.esc c
(Boolean-valued).
.
.TP
.REG .j
Adjustment mode encoded as an integer;
see
.request .ad
and
.request .na .
.
Do not interpret or perform arithmetic on its value.
.
.TP
.REG .k
Horizontal drawing position relative to indentation.
.
.TP
.REG .kern
Pairwise kerning is enabled (Boolean-valued).
.
.TP
.REG .l
Line length;
see
.request .ll .
.
.TP
.REG .L
Line spacing;
see
.request .ls .
.
.TP
.REG .lg
Ligature mode.
.
.TP
.REG .linetabs
Line-tabs mode is enabled (Boolean-valued).
.
.TP
.REG .ll
Line length applicable to the pending output line.
.
.TP
.REG .lt
Title length.
.
.TP
.REG .m
Stroke color (string-valued);
see
.request .gcolor
and
.esc m .
.
Empty if the stroke color is the default.
.
.TP
.REG .M
Fill color (string-valued);
see
.request .fcolor
and
.esc M .
.
Empty if the fill color is the default.
.
.TP
.REG .n
Length of formatted output on previous output line.
.
.TP
.REG .ne
Amount of vertical space required by last
.request .ne
that caused a trap to be sprung;
also see
.register .trunc .
.
.TP
.REG .nm
Output line numbering is enabled (Boolean-valued).
.
.TP
.REG .nn
Count of output lines remaining to have numbering suppressed.
.
.TP
.REG .ns
No-space mode is enabled (Boolean-valued).
.
.TP
.REG .o
Page offset;
see
.request .po .
.
.TP
.REG .O
Output suppression nesting level;
see
.esc O .
.
.TP
.REG .p
Page length;
see
.request .pl .
.
.TP
.REG .P
The page is selected for output (Boolean-valued);
see
.I @g@troff
.B \-o
option.
.
.TP
.REG .pe
Page ejection is in progress (Boolean-valued).
.
.TP
.REG .pn
Number of the next page.
.
.TP
.REG .ps
Type size in scaled points.
.
.TP
.REG .psr
Most recently requested type size in scaled points;
see
.request .ps
and
.esc s .
.
.TP
.REG .pvs
Post-vertical line spacing.
.
.TP
.REG .R
Count of available unused registers;
always 10,000 in GNU
.IR troff . \" GNU
.
.TP
.REG .rj
Count of lines remaining to be right-aligned.
.
.TP
.REG .s
Type size in points as a decimal fraction (string-valued);
see
.request .ps
and
.esc s .
.
.TP
.REG .slant
Slant of font in degrees;
see
.esc S .
.
.TP
.REG .sr
Most recently requested type size in points as a decimal fraction
(string-valued);
see
.request .ps
and
.esc s .
.
.TP
.REG .ss
Size of minimal inter-word space in twelfths of the space width of the
selected font.
.
.TP
.REG .sss
Size of additional inter-sentence space in twelfths of the space width
of the selected font.
.
.TP
.REG .sty
Selected abstract style (string-valued);
see
.request .ft
and
.esc f .
.
.TP
.REG .t
Distance to next vertical position trap;
see
.request .wh
and
.request .ch .
.
.TP
.REG .T
An output device was explicitly selected (Boolean-valued);
see
.I @g@troff
.B \-T
option.
.
.TP
.REG .tabs
Representation of tab settings suitable for use as argument to
.request .ta
(string-valued).
.
.TP
.REG .trunc
Amount of vertical space truncated by the most recently sprung
vertical position trap,
or,
if the trap was sprung by an
.request .ne ,
minus the amount of vertical motion produced by
.request .ne ;
also see
.register .ne .
.
.TP
.REG .u
Filling is enabled (Boolean-valued);
see
.request .fi
and
.request .nf .
.
.TP
.REG .U
Unsafe mode is enabled (Boolean-valued);
see
.I @g@troff
.B \-U
option.
.
.TP
.REG .v
Vertical line spacing;
see
.request .vs .
.
.TP
.REG .V
Vertical motion quantum of the output device in basic units.
.
.TP
.REG .vpt
Vertical position traps are enabled (Boolean-valued).
.
.TP
.REG .w
Width of previous glyph formatted in the environment.
.
.TP
.REG .warn
Sum of the numeric codes of enabled warning categories.
.
.TP
.REG .x
Major version number of the running
.I @g@troff
formatter.
.
.TP
.REG .y
Minor version number of the running
.I @g@troff
formatter.
.
.TP
.REG .Y
Revision number of the running
.I @g@troff
formatter.
.
.TP
.REG .z
Name of diversion (string-valued).
.
Empty if output is directed to the top-level diversion.
.
.TP
.REG .zoom
Zoom multiplier of current font
(in thousandths;
zero if no magnification);
see
.request .fzoom .
.LE
.
.
.\" ====================================================================
.SS "Writable predefined registers"
.\" ====================================================================
.
Several registers are predefined but also modifiable;
some are updated upon interpretation of certain requests or escape
sequences.
.
Date- and time-related registers are set to the local time as determined
by
.MR localtime 3
when the formatter launches.
.
This initialization can be overridden by
.I \%SOURCE_DATE_EPOCH
and
.IR TZ ;
see section \[lq]Environment\[rq] of
.MR groff @MAN1EXT@ .
.
.
.P
.LS
.
.TP 15n
.REG $$
Process ID of
.IR @g@troff .
.
.TP
.REG %
Page number.
.
.TP
.REG c.
Input line number.
.
.TP
.REG ct
Union of character types of each glyph rendered into dummy environment
by
.esc w .
.
.TP
.REG dl
Width of last closed diversion.
.
.TP
.REG dn
Height of last closed diversion.
.
.TP
.REG dw
Day of the week (1\[en]7;
1 is Sunday).
.
.TP
.REG dy
Day of the month (1\[en]31).
.
.TP
.REG hours
Count of hours elapsed since midnight (0\[en]23).
.
.TP
.REG hp
Horizontal drawing position relative to start of input line.
.
.TP
.REG llx
Lower-left
.I x
coordinate
(in PostScript units)
of PostScript image;
see
.request .psbb .
.
.TP
.REG lly
Lower-left
.I y
coordinate
(in PostScript units)
of PostScript image;
see
.request .psbb .
.
.TP
.REG ln
Output line number;
see
.request .nm .
.
.TP
.REG lsn
Count of leading spaces on input line.
.
.TP
.REG lss
Amount of horizontal space corresponding to leading spaces on input
line.
.
.TP
.REG minutes
Count of minutes elapsed in the hour (0\[en]59).
.
.TP
.REG mo
Month of the year (1\[en]12).
.
.TP
.REG nl
Vertical drawing position.
.
.TP
.REG opmaxx
.TP
.REG opmaxy
.TP
.REG opminx
.TP
.REG opminy
These four registers mark the top left- and bottom right-hand corners of
a rectangle encompassing all formatted output on the page.
.
They are reset to \-1 by
.B \[rs]O0
or
.BR \[rs]O1 .
.
.TP
.REG rsb
As
.register sb ,
adding maximum glyph height to measurement.
.
.TP
.REG rst
As
.register st ,
adding maximum glyph depth to measurement.
.
.TP
.REG sb
Maximum displacement of text baseline below its original position
after rendering into dummy environment by
.esc w .
.
.TP
.REG seconds
Count of seconds elapsed in the minute (0\[en]60). \" not 59; see POSIX
.
.TP
.REG skw
Skew of last glyph rendered into dummy environment by
.esc w .
.
.TP
.REG slimit
The maximum depth of
.IR @g@troff 's
internal input stack.
.
If \[<=]0,
there is no limit:
recursion can continue until available memory is exhausted.
.
The default is 1,000.
.
.TP
.REG ssc
Subscript correction of last glyph rendered into dummy environment by
.esc w .
.
.TP
.REG st
Maximum displacement of text baseline above its original position
after rendering into dummy environment by
.esc w .
.
.TP
.REG systat
Return value of
.I system()
function; see
.request .sy .
.
.TP
.REG urx
Upper-right
.I x
coordinate
(in PostScript units)
of PostScript image;
see
.request .psbb .
.
.TP
.REG ury
Upper-right
.I y
coordinate
(in PostScript units)
of PostScript image;
see
.request .psbb .
.
.TP
.REG year
Gregorian year.
.
.TP
.REG yr
Gregorian year minus 1900.
.LE
.
.
.\" ====================================================================
.SH "Using fonts"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Using Fonts".
In digital typography,
a
.I font
is a collection of characters in a specific typeface that a device can
render as glyphs at a desired size.
.
(Terminals and some output devices have fonts that render at only one or
two sizes.
.
As examples of the latter,
take the
.I groff
.B lj4
device's
Lineprinter,
and
.BR lbp 's
Courier and Elite faces.)
.
.
A
.I roff
formatter can change typefaces at any point in the text.
.
The basic faces are a set of
.I styles
combining upright and slanted shapes with normal and heavy stroke
weights:
.RB \[lq] R \[rq],
.RB \[lq] I \[rq],
.RB \[lq] B \[rq],
and
.RB \[lq] BI \[rq]\[em]\c
these stand for
.I roman,
.I bold,
.I italic,
and
.I bold-italic.
.
For linguistic text,
GNU
.I troff \" GNU
groups typefaces into
.I families
containing each of these styles.
.
(Font designers prepare families such that the styles share esthetic
properties.)
.
A
.I "text font"
is thus often a family combined with a style,
but it need not be:
consider the
.B ps
and
.B pdf
devices'
.B ZCMI
(Zapf Chancery Medium italic)\[em]\c
often,
no other style of Zapf Chancery Medium is provided.
.
On typesetting devices,
at least one
.I "special font"
is available,
comprising
.I unstyled
glyphs for mathematical operators and other purposes.
.
.
.P
Like AT&T
.I troff, \" AT&T
GNU
.I troff \" GNU
does not itself load or manipulate a digital font file;
.\" @footnote{Historically, the fonts @code{troff}s dealt with were not
.\" Free Software or, as with the Graphic Systems C/A/T, did not even
.\" exist in the digital domain.}
instead it
works with a
.I font description file
that characterizes it,
including its glyph repertoire and the
.I metrics
(dimensions) of each glyph.
.
This information permits the formatter to accurately place glyphs with
respect to each other.
.
Before using a font description,
the formatter associates it with a
.I "mounting position,"
a place in an ordered list of available typefaces.
.
So that a document need not be strongly coupled to a specific font
family,
in GNU
.I troff \" GNU
an output device can associate a style in the abstract sense with a
mounting position.
.
Thus the default family can be combined with a style dynamically,
producing a
.I "resolved font name."
.
.
.P
Fonts often have trademarked names,
and even Free Software fonts can require renaming upon modification.
.
.I groff
maintains a convention that a device's serif font family is given the
name
.B T
(\[lq]Times\[rq]),
its sans-serif family
.B H
(\[lq]Helvetica\[rq]),
and its
monospaced family
.B C
(\[lq]Courier\[rq]).
.
Historical inertia has driven
.IR groff 's
font identifiers to short uppercase abbreviations of font names,
as with
.BR TR ,
.BR TB ,
.BR TI ,
.BR TBI ,
and a special font
.BR S .
.
.
.P
The default family used with abstract styles can be changed at any time;
initially,
it
.RB is\~ T .
.
Typically,
abstract styles are arranged in the first four mounting positions in the
order shown above.
.
The default mounting position,
and therefore style,
is always
.B 1
.RB ( R ).
.
By issuing appropriate formatter instructions,
you can override these defaults before your document writes its first
glyph.
.
.
.P
Terminal output devices cannot change font families and lack special
fonts.
.
They support style changes by overstriking,
or by altering ISO\~6429/\:ECMA-48
.I "graphic renditions"
(character cell attributes).
.\" END Keep (roughly) parallel with groff.texi node "Using Fonts".
.
.
.\" ====================================================================
.SH Hyphenation
.\" ====================================================================
.
When filling,
.I groff
hyphenates words as needed at user-specified and automatically
determined hyphenation points.
.
Explicitly hyphenated words such as \[lq]mother-in-law\[rq] are always
eligible for breaking after each of their hyphens.
.
The hyphenation
.RB character\~ \[rs]%
and non-printing break
.RB point\~ \[rs]:
escape sequences may be used to control the hyphenation and breaking of
individual words.
.
The
.B .hw
request sets user-defined hyphenation points for specified words at any
subsequent occurrence.
.
Otherwise,
.I groff
determines hyphenation points automatically by default.
.
.
.P
Several requests influence automatic hyphenation.
.
Because conventions vary,
a variety of hyphenation modes is available to the
.B .hy
request;
these determine whether hyphenation will apply to a word prior to
breaking a line at the end of a page
(more or less;
see below for details),
and at which positions within that word automatically determined
hyphenation points are permissible.
.
The default is
.RB \[lq] 1 \[rq]
for historical reasons,
but this is not an appropriate value for the English hyphenation
patterns used by
.IR groff ;
localization macro files loaded by
.I troffrc
and macro packages often override it.
.
.
.TP
.B 0
disables hyphenation.
.
.
.TP
.B 1
enables hyphenation except after the first and before the last character
of a word.
.
.
.P
The remaining values \[lq]imply\[rq]
.BR 1 ;
that is,
they enable hyphenation under the same conditions as
.RB \[lq] ".hy 1" \[rq],
and then apply or lift restrictions relative to that basis.
.
.
.TP
.B 2
disables hyphenation of the last word on a page.
.
(Hyphenation is prevented if the next page location trap is closer to
the vertical drawing position than the next text baseline would be.
.
See section \[lq]Traps\[rq] below.)
.
.
.TP
.B 4
disables hyphenation before the last two characters of a word.
.
.
.TP
.B 8
disables hyphenation after the first two characters of a word.
.
.
.TP
.B 16
enables hyphenation before the last character of a word.
.
.
.TP
.B 32
enables hyphenation after the first character of a word.
.
.
.P
Apart from value\~2,
restrictions imposed by the hyphenation mode are
.I not
respected for words whose hyphenations have been specified with the
hyphenation character
.RB (\[lq] \|\[rs]% \[rq]
by default)
or the
.B .hw
request.
.
.
.P
Nonzero values are additive.
.
For example,
mode\~12 causes
.I groff
to hyphenate neither the last two nor the first two characters of a
word.
.
Some values cannot be used together because they contradict;
for instance,
values 4 and\~16,
and values 8 and\~32.
.
As noted,
it is superfluous to add\~1 to any non-zero even mode.
.
.
.br
.ne 2v
.P
The places within a word that are eligible for hyphenation are
determined by language-specific data
.RB ( .hla ,
.BR .hpf ,
and
.BR .hpfa )
and lettercase relationships
.RB ( .hcode
and
.BR .hpfcode ).
.
Furthermore,
hyphenation of a word might be suppressed due to a limit on
consecutive hyphenated lines
.RB ( .hlm ),
a minimum line length threshold
.RB ( .hym ),
or because the line can instead be adjusted with additional inter-word
space
.RB ( .hys ).
.
.
.\" ====================================================================
.SH Localization
.\" ====================================================================
.
The set of hyphenation patterns is associated with the hyphenation
language set by the
.B .hla
request.
.
The
.B .hpf
request is usually invoked by a localization file loaded by the
.I troffrc
file.
.
.I groff
provides localization files for several languages;
see
.MR groff_tmac @MAN5EXT@ .
.
.
.\" ====================================================================
.SH "Writing macros"
.\" ====================================================================
.
The
.B .de
request defines a macro named for its argument.
.
If that name already exists as an alias,
the target of the alias is redefined;
see section \[lq]Strings\[rq] above.
.
.I @g@troff
enters \[lq]copy mode\[rq]
(see below),
storing subsequent input lines as the definition.
.
If the optional second argument is not specified,
the definition ends with the control line
.RB \[lq] .. \[rq]\&
(two dots).
.
Alternatively,
a second argument names a macro whose call syntax ends the definition;
this \[lq]end macro\[rq] is then called normally.
.
Spaces or tabs are permitted after the first control character in the
line containing this ending token,
but a tab immediately after the token prevents its recognition as the
end of a macro definition.
.
Macro definitions can be nested if they use distinct end macros or if
their ending tokens are sufficiently escaped.
.
An end macro need not be defined until it is called.
.
This fact enables a nested macro definition to begin inside one macro
and end inside another.
.
.
.P
Variants of
.B .de
disable compatibility mode and/or indirect the names of the macros
specified for definition or termination:
these are
.BR .de1 ,
.BR .dei ,
and
.BR .dei1 .
.
Append to macro definitions with
.BR .am ,
.BR .am1 ,
.BR .ami ,
and
.BR .ami1 .
.
The
.BR .als ,
.BR .rm ,
and
.B .rn
requests create an alias of,
remove,
and rename a macro,
respectively.
.
.B .return
stops the execution of a macro immediately,
returning to the enclosing context.
.
.
.\" ====================================================================
.SS Parameters
.\" ====================================================================
.
Macro call and string interpolation parameters can be accessed using
escape sequences starting with
.RB \[lq] \|\[rs]$ \[rq].
.
The
.B \[rs]n[.$]
read-only register stores the count of parameters available to a macro
or string;
its value can be changed by the
.B .shift
request,
which dequeues parameters from the current list.
.
The
.B \[rs]$0
escape sequence interpolates the name by which a macro was called.
.
Applying string interpolation to a macro does not change this name.
.
.
.\" ====================================================================
.SS "Copy mode"
.\" ====================================================================
.
When
.I @g@troff
processes certain requests,
most importantly those which define or append to a macro or string,
it does so in
.IR "copy mode" :
it copies the characters of the definition into a dedicated storage
region,
interpolating the escape sequences
.BR \[rs]n ,
.BR \[rs]g ,
.BR \[rs]$ ,
.BR \[rs]* ,
.BR \[rs]V ,
and
.B \[rs]?\&
normally;
interpreting
.BI \[rs] newline
immediately;
discarding comments
.B \[rs]"
and
.BR \[rs]# ;
interpolating the current leader,
escape,
or tab character with
.BR \[rs]a ,
.BR \[rs]e ,
and
.BR \[rs]t ,
respectively;
and storing all other escape sequences in an encoded form.
.
The complement of copy mode\[em]a
.I roff
formatter's behavior when not defining or appending to a macro,
string,
or diversion\[em]where all macros are interpolated,
requests invoked,
and valid escape sequences processed immediately upon recognition,
can be termed
.IR "interpretation mode" .
.
.
.P
The escape character,
.B \[rs]
by default,
can escape itself.
.
This enables you to control whether a given
.BR \[rs]n ,
.BR \[rs]g ,
.BR \[rs]$ ,
.BR \[rs]* ,
.BR \[rs]V ,
or
.B \[rs]?\&
escape sequence is interpreted at the time the macro containing it is
defined,
or later when the macro is called.
.
.
.P
You can think of
.B \[rs]\[rs]
as a \[lq]delayed\[rq] backslash;
it is the escape character followed by a backslash from which the escape
character has removed its special meaning.
.
Consequently,
.B \[rs]\[rs]
is not an escape sequence in the usual sense.
.
In any escape sequence
.BI \[rs] X
that
.I @g@troff
does not recognize,
the escape character is ignored and
.IR X \~is
output.
.
An unrecognized escape sequence causes a warning in category
.RB \%\[lq] escape \[rq],
with two exceptions,
.B \[rs]\[rs]
being one.
.
The other is
.BR \[rs]. ,
which escapes the control character.
.
It is used to permit nested macro definitions to end without a named
macro call to conclude them.
.
Without a syntax for escaping the control character,
this would not be possible.
.
.I roff
documents should not use the
.B \[rs]\[rs]
or
.B \[rs].\&
character sequences outside of copy mode;
they serve only to obfuscate the input.
.
Use
.B \[rs]e
to represent the escape character,
.B \[rs][rs]
to obtain a backslash glyph,
and
.B \[rs]&
before
.B .\&
and
.B \[aq]
where
.I @g@troff
expects them as control characters if you mean to use them literally.
.
.
.br
.ne 2v
.P
Macro definitions can be nested to arbitrary depth.
.
In
.RB \[lq] \|\[rs]\[rs] \[rq],
each escape character is interpreted twice\[em]once in copy mode,
when the macro is defined,
and once in interpretation mode,
when the macro is called.
.
This fact leads to exponential growth in the quantity of escape
characters required to delay interpolation of
.BR \[rs]n ,
.BR \[rs]g ,
.BR \[rs]$ ,
.BR \[rs]* ,
.BR \[rs]V ,
and
.B \[rs]?\&
at each nesting level.
.
An alternative is to use
.BR \[rs]E ,
which represents an escape character that is not interpreted in copy
mode.
.
Because
.B \[rs].\&
is not a true escape sequence,
we can't use
.B \[rs]E
to keep
.RB \[lq] ..\& \[rq]
from ending a macro definition prematurely.
.
If the multiplicity of backslashes complicates maintenance,
use end macros.
.
.
.\" ====================================================================
.SH Traps
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Traps".
.I Traps
are locations in the output,
or conditions on the input that,
when reached or fulfilled,
call a specified macro.
.
A
.I "vertical position trap"
calls a macro when the formatter's vertical drawing position reaches or
passes,
in the downward direction,
a certain location on the output page or in a diversion.
.
Its applications include setting page headers and footers,
body text in multiple columns,
and footnotes.
.
These traps can occur at a given location on the page
.RB ( .wh ,\~ .ch );
at a given location in the current diversion
.RB ( .dt )\[em]together,
these are known as
vertical position traps,
which can be disabled and re-enabled
.RB ( .vpt ).
.
.
.P
A diversion is not formatted in the context of a page,
so it lacks page location traps;
instead it can have a
.I "diversion trap."
.
There can exist at most one such vertical position trap per diversion.
.
.
.P
Other kinds of trap can be planted
at a blank line
.RB ( .blm );
at a line with leading space characters
.RB ( .lsm );
after a certain number of productive input lines
.RB ( .it ,\~ .itc );
or at the end of input
.RB ( .em ).
.
Macros called by traps are passed no arguments.
.
Setting a trap is also called
.I planting
one.
.
It is said that a trap is
.I sprung
if its condition is fulfilled.
.\" END Keep (roughly) parallel with groff.texi node "Traps".
.
.
.br
.ne 5v
.P
Registers associated with trap management include
vertical position trap enablement status
.RB ( \[rs]n[.vpt] ),
distance to the next trap
.RB ( \[rs]n[.t] ),
amount of needed
.RB ( .ne -requested)
space that caused the most recent vertical position trap to be sprung
.RB ( \[rs]n[.ne] ),
amount of needed space truncated from the amount requested
.RB ( \[rs]n[.trunc] ),
page ejection status
.RB ( \[rs]n[.pe] ),
and
leading space count
.RB ( \[rs]n[.lsn] )
with its corresponding amount of motion
.RB ( \[rs]n[.lss] ).
.
.
.\" ====================================================================
.SS "Page location traps"
.\" ====================================================================
.
A
.I "page location trap"
is a vertical position trap that applies to
the page;
that is,
to undiverted output.
.
Many can be present;
manage them with
the
.B wh
and
.B ch
requests.
.
Non-negative page locations given to these requests set the trap
relative to the top of the page;
negative values set the trap relative to the bottom of the page.
.
It is not possible to plant a trap less than one basic unit from the
page bottom:
a location of \[lq]\-0\[rq] is interpreted as \[lq]0\[rq],
the top of the page.
.
An existing
.I visible
trap
(see below)
at the same location is removed;
this is
.BR .wh 's
sole function if its second argument is missing.
.
.
.P
A trap is sprung only if it is
.I visible,
meaning that its location is reachable on the page and it is not hidden
by another trap at the same location already planted there.
.
(A trap planted at \[lq]20i\[rq] or \[lq]\-30i\[rq] will not be sprung
on a page of length \[lq]11i\[rq].)
.
.
.P
A trap above the top or at or below the bottom of the page can be made
visible by either moving it into the page area or increasing the page
length so that the trap is on the page.
.
Negative trap values always use the
.I current
page length;
they are not converted to an absolute vertical position.
.
Use
.B .ptr
to dump page location traps to the standard error stream;
their positions are reported in basic units.
.
.
.br
.ne 6v
.\" ====================================================================
.SS "The implicit page trap"
.\" ====================================================================
.
An
.I implicit page trap
always exists in the top-level diversion;
it works like a trap in some ways but not others.
.
Its purpose is to eject the current page and start the next one.
.
It has no name,
so it cannot be moved or deleted with
.B wh
or
.B ch
requests.
.
You cannot hide it by placing another trap at its location,
and can move it only by redefining the page length with
.BR .pl .
.
Its operation is suppressed when vertical page traps are disabled with
the
.B vpt
request.
.
.
.\" ====================================================================
.SH Diversions
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Diversions".
In
.I roff
systems it is possible to format text as if for output,
but instead of writing it immediately,
one can
.I divert
the formatted text into a named storage area.
.
It is retrieved later by specifying its name after a control character.
.
The same name space is used for such
.I diversions
as for strings and macros;
see section \[lq]Identifiers\[rq] above.
.
Such text is sometimes said to be \[lq]stored in a macro\[rq],
but this coinage obscures the important distinction between macros and
strings on one hand and diversions on the other;
the former store
.I unformatted
input text,
and the latter capture
.I formatted
output.
.
Diversions also do not interpret arguments.
.
Applications of diversions include \[lq]keeps\[rq]
(preventing a page break from occurring at an inconvenient place by
forcing a set of output lines to be set as a group),
footnotes,
tables of contents,
and indices.
.
For orthogonality it is said that GNU
.I troff \" GNU
is in the
.I top-level diversion
if no diversion is active
(that is,
formatted output is being \[lq]diverted\[rq] immediately to the output
device.
.
.
.P
Dereferencing an undefined diversion will create an empty one of that
name and cause a warning in category
.B mac
to be emitted.
(see section \[lq]Warnings\[rq] in
.MR @g@troff @MAN1EXT@ ).
.
A diversion does not exist for the purpose of testing with the
.B d
conditional operator until its initial definition ends
(see subsection \[lq]Conditional expressions\[rq] above).
.\" The following requests are used to create and alter diversions.
.\" END Keep (roughly) parallel with groff.texi node "Diversions".
.
.
.P
The
.B di
request creates a diversion,
including any partially collected line.
.
.B da
appends to a diversion,
creating one if it does not already exist.
.
If the diversion's name already exists as an alias,
the target of the alias is replaced or appended to;
see section \[lq]Strings\[rq] above.
.
.B box
and
.B boxa
works similarly,
but ignore partially collected lines.
.
Call any of these macros again without an argument to end the diversion.
.
.
.br
.ne 2v
.P
Diversions can be nested.
.
The registers
.BR .d ,
.BR .z ,
.BR dn ,
and
.B dl
report information about the current
(or last closed)
diversion.
.
.B .h
is meaningful in diversions,
including the top level.
.
.
.P
The
.B \[rs]!\%
and
.B \[rs]?\%
escape sequences and
.B output
request escape from a diversion,
the first two to the enclosing level and the last to the top level.
.
This facility is termed
.IR "transparent embedding" .
.
.
.P
The
.B asciify
and
.B unformat
requests reprocess diversions.
.\" XXX: That's a weak statement.  What we need is a `for` request and
.\" a new conditional operator that tests whether an item in a node list
.\" is an (otherwise unrepresentable) node.  See Savannah #62264.
.
.
.\" ====================================================================
.SH "Punning names"
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Punning names".
Macros,
strings,
and diversions share a name space;
see section \[lq]Identifiers\[rq] above.
.
Internally,
the same mechanism is used to store them.
.
You can thus call a macro with string interpolation syntax and vice
versa.
.
Interpolating a string does not hide existing macro arguments.
.
The sequence
.B \[rs]\[rs]
can be placed at the end of a line in a macro definition or,
within a macro definition,
immediately after the interpolation of a macro as a string to suppress
the effect of a newline.
.\" END Keep (roughly) parallel with groff.texi node "Punning names".
.
.
.\" ====================================================================
.SH Environments
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Environments".
Environments store most of the parameters that control text processing.
.
A default environment named
.RB \[lq] 0 \[rq]
exists when
.I @g@troff
starts up;
it is modified by formatting-related requests and escape sequences.
.
.
.P
You can create new environments and switch among them.
.
Only one is current at any given time.
.
Active environments are managed using a
.I stack,
a data structure supporting \[lq]push\[rq] and \[lq]pop\[rq] operations.
.
The current environment is at the top of the stack.
.
The same environment name can be pushed onto the stack multiple times,
possibly interleaved with others.
.
Popping the environment stack does not destroy the current environment;
it remains accessible by name and can be made current again by pushing
it at any time.
.
Environments cannot be renamed or deleted,
and can only be modified when current.
.
To inspect the environment stack,
use the
.B pev
request;
see section \[lq]Debugging\[rq] below.
.
.
.P
Environments store the following information.
.
.
.IP \[bu] 2n
a partially collected line, if any
.
.
.IP \[bu]
data about the most recently output glyph and line
(registers
.BR .cdp ,
.BR .cht ,
.BR .csk ,
.BR .n ,
.BR .w )
.
.
.IP \[bu]
typeface parameters
(size,
family,
style,
height and slant,
inter-word and inter-sentence space sizes)
.
.
.IP \[bu]
page parameters
(line length,
title length,
vertical spacing,
line spacing,
indentation,
line numbering,
centering,
right-alignment,
underlining,
hyphenation parameters)
.
.
.IP \[bu]
filling enablement;
adjustment enablement and mode
.
.
.IP \[bu]
tab stops;
tab,
leader,
escape,
control,
no-break control,
hyphenation,
and
margin characters
.
.
.IP \[bu]
input line traps
.
.
.IP \[bu]
stroke and fill colors
.
.
.P
The
.B ev
request pushes to and pops from the environment stack,
while
.B evc
copies a named environment's contents to the current one.
.\" END Keep (roughly) parallel with groff.texi node "Environments".
.
.
.\" ====================================================================
.SH Underlining
.\" ====================================================================
.
In
.I RUNOFF
(see
.MR roff @MAN7EXT@ ),
underlining,
even of lengthy passages,
was straightforward because only fixed-pitch printing devices were
targeted.
.
Typesetter output posed a greater challenge.
.
There exists a
.I groff
request
.B .ul
(see above)
that underlines subsequent source lines on terminal devices,
but on typesetters,
it selects an italic font style instead.
.
.
The
.I ms
macro package
(see
.MR groff_ms @MAN7EXT@ )
offers a macro
.BR .UL ,
but it too produces the desired effect only on typesetters,
and has other limitations.
.
.
.P
One could adapt
.IR ms 's
approach to the construction of a macro as follows.
.
.RS
.EX
\&.de UNDERLINE
\&. ie n \[rs]\[rs]$1\[rs]f[I]\[rs]\[rs]$2\[rs]f[P]\[rs]\[rs]$3
\&. el \[rs]\[rs]$1\[rs]Z\[aq]\[rs]\[rs]$2\[aq]\[rs]v\[aq].25m\[aq]\
\[rs]D\[aq]l \[rs]w\[aq]\[rs]\[rs]$2\[aq]u 0\[aq]\[rs]v\[aq]\-.25m\
\[aq]\[rs]\[rs]$3
\&..
.EE
.RE
.
If
.MR doclifter 1
makes trouble, change the macro name
.B UNDERLINE
into some 2-letter word, like
.BR Ul .
.
Moreover,
change the form of the font selection escape sequence from
.B \[rs]f[P]
to
.BR \[rs]fP .
.
.
.\" ====================================================================
.SS "Underlining without macro definitions"
.\" ====================================================================
.
If one does not want to use macro definitions,
e.g.,
when
.I doclifter
gets lost,
use the following.
.
.RS
.EX
\&.ds u1 before
\&.ds u2 in
\&.ds u3 after
\&.ie n \[rs]*[u1]\[rs]f[I]\[rs]*[u2]\[rs]f[P]\[rs]*[u3]
\&.el \[rs]*[u1]\[rs]Z\[aq]\[rs]*[u2]\[aq]\[rs]v\[aq].25m\[aq]\[rs]D\
\[aq]l \[rs]w\[aq]\[rs]*[u2]\[aq]u 0\[aq]\[rs]v\[aq]\-.25m\[aq]\[rs]*\
[u3]
.EE
.RE
.
.ne 2v
When using
.IR doclifter ,
it might be necessary to change syntax forms such as
.B \e[xy]
and
.B \e*[xy]
to those supported by AT&T
.IR troff :
.B \e*(xy
and
.BR \e(xy ,
and so on.
.
.
.P
Then these lines could look like
.RS
.EX
\&.ds u1 before
\&.ds u2 in
\&.ds u3 after
\&.ie n \[rs]*[u1]\[rs]fI\[rs]*(u2\[rs]fP\[rs]*(u3
\&.el \[rs]*(u1\[rs]Z\[aq]\[rs]*(u2\[aq]\[rs]v\[aq].25m\[aq]\[rs]D\
\[aq]l \[rs]w\[aq]\[rs]*(u2\[aq]u 0\[aq]\[rs]v\[aq]\-.25m\[aq]\[rs]*(u3
.EE
.RE
.
.
.P
The result looks like
.RS
.ft CR
before
\z\[ul]i\
\z\[ul]n
after
.ft R
.RE
.
.
.\" ====================================================================
.SS "Underlining by overstriking with \e(ul"
.\" ====================================================================
.
The
.B \[rs]z
escape sequence writes a glyph without advancing the
drawing position,
enabling overstriking.
.
Thus,
.BI \[rs]z c \[rs](ul
formats
.I c
with an underrule glyph on top of it.
.
Video terminals implement the underrule by setting a character cell's
underline attribute,
so this technique works in both
.I nroff \" mode
and
.I troff \" mode
modes.
.
.
.P
Long words may then look intimidating in the input;
a clarifying approach might be to use the input line continuation escape
sequence
.BI \[rs] newline
to place each underlined character on its own input line.
.
Thus,
.
.RS
.EX
\&.nf
\[rs]&\[rs]fB: ${\[rs]fIvar\[rs]fR\[rs]c
\[rs]zo\[rs](ul\[rs]
\[rs]zp\[rs](ul\[rs]c
\[rs]&\[rs]fIvalue\[rs]fB}
\&.fi
.EE
.RE
.
produces
.
.RS
.EX
.BI ": ${" var \c
\zo\(ul\
\zp\(ul\c
.IB value }
.EE
.RE
.
as output.
.
.
.\" ====================================================================
.SH "Compatibility mode"
.\" ====================================================================
.
The differences between the
.I roff
language recognized by GNU
.I troff \" GNU
and that of AT&T
.IR troff , \" AT&T
as well as the device,
font,
and device-independent intermediate output formats described by
CSTR\~#54 are documented in
.MR groff_diff @MAN7EXT@ .
.
.I groff
provides an AT&T compatibility mode.
.
The
.request .cp
request and registers
.B .C
and
.B .cp
set and test the enablement of this mode.
.
.
.\" ====================================================================
.SH Debugging
.\" ====================================================================
.
.\" BEGIN Keep (roughly) parallel with groff.texi node "Debugging".
Preprocessors use the
.B .lf
request to preserve the identities of line numbers and names of input
files.
.
.I groff
emits a variety of error diagnostics and supports several categories of
warning;
the output of these can be selectively suppressed with
.B .warn
(and see the
.BR \-E ,
.BR \-w ,
and
.B \-W
options of
.MR @g@troff @MAN1EXT@ ).
.
A trace of the formatter's input processing stack can be emitted when
errors or warnings occur by means of
.MR @g@troff @MAN1EXT@ 's
.B \-b
option,
or produced on demand with the
.request .backtrace
request.
.
.BR .tm ,
.BR .tmc ,
and
.B .tm1
can be used to emit customized diagnostic messages or for
instrumentation while troubleshooting.
.
.B .ex
and
.B .ab
cause early termination with successful and error exit codes
respectively,
to halt further processing when continuing would be fruitless.
.
Examine the state of the formatter with requests that write lists of
defined names\[em]macros,
strings,
and
.RB diversions\[em]( .pm );
environments
.RB ( .pev ),
registers
.RB ( .pnr ),
and page location traps
.RB ( .ptr )
to the standard error stream.
.\" END Keep (roughly) parallel with groff.texi node "Debugging".
.
.
.\" ====================================================================
.SH Authors
.\" ====================================================================
.
This document was written by
by Trent A.\& Fisher,
Werner Lemberg,
and
.MT g.branden\:.robinson@\:gmail\:.com
G.\& Branden Robinson
.ME .
.
Section \[lq]Underlining\[rq] was primarily written by
.MT groff\-bernd\:.warken\-72@\:web\:.de
Bernd Warken
.ME .
.
.
.\" ====================================================================
.SH "See also"
.\" ====================================================================
.
.ne 2v
.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].
.
.
.br
.ne 4v
.P
\[lq]Troff User's Manual\[rq]
by Joseph F.\& Ossanna,
1976
(revised by Brian W.\& Kernighan,
1992),
AT&T Bell Laboratories Computing Science Technical Report No.\& 54,
widely called simply \[lq]CSTR\~#54\[rq],
documents the language,
device and font description file formats,
and device-independent output format
referred to collectively in
.I groff
documentation as
.RI \[lq]AT&T\~ troff \[rq].
.
.
.br
.ne 3v
.P
\[lq]A Typesetter-independent TROFF\[rq]
by Brian W.\& Kernighan,
1982,
AT&T Bell Laboratories Computing Science Technical Report No.\& 97
(CSTR\~#97),
provides additional insights into the
device and font description file formats
and device-independent output format.
.
.
.TP
.MR groff @MAN1EXT@
is the preferred interface to the
.I groff
system;
it manages the pipeline that carries a source document through
preprocessors,
the
.I @g@troff
formatter,
and an output driver to viewable or printable form.
.
It also exhaustively lists the man pages provided with the GNU
.I roff
system.
.
.
.TP
.MR groff_char @MAN7EXT@
discusses character encoding issues,
escape sequences that produce glyphs,
and enumerates
.IR groff 's
predefined special character escape sequences.
.
.
.TP
.MR groff_diff @MAN7EXT@
covers differences between the
GNU
.I troff \" GNU
formatter,
its device and font description file formats,
its device-independent output format,
and those of AT&T
.IR troff ,\" AT&T
whose design it reimplements.
.
.
.TP
.MR groff_font @MAN5EXT@
describes the formats of the files that describe devices
.RI ( DESC )
and fonts.
.
.
.TP
.MR groff_tmac @MAN5EXT@
surveys macro packages provided with
.IR groff ,
describes how documents can take advantage of them,
offers guidance on writing macro packages and using diversions,
and includes historical information on macro package naming conventions.
.
.
.TP
.MR roff @MAN7EXT@
presents a detailed history of
.I roff
systems and summarizes concepts common to them.
.
.
.\" Restore compatibility mode (for, e.g., Solaris 10/11).
.cp \n[*groff_groff_7_man_C]
.do rr *groff_groff_7_man_C
.
.
.\" Local Variables:
.\" fill-column: 72
.\" mode: nroff
.\" End:
.\" vim: set filetype=groff textwidth=72: