.ig
groff_diff.man

Last update : 9 Dec 2001

This file is part of groff, the GNU roff type-setting system.

Copyright (C) 2000, 2001 Free Software Foundation, Inc.
written by James Clark

modified by Werner Lemberg <wl@gnu.org>
            Bernd Warken <bwarken@mayn.de>

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with the
Invariant Sections being this .ig-section and AUTHOR, 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.
..
.
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.\" --------------------------------------------------------------------
.\" Title
.\" --------------------------------------------------------------------
.
.TH GROFF_DIFF @MAN7EXT@ "@MDATE@" "Groff Version @VERSION@"
.SH NAME
groff_diff \- differences between GNU troff and classical troff
.
.
.\" --------------------------------------------------------------------
.SH DESCRIPTION
.\" --------------------------------------------------------------------
.
This manual page describes the language differences between
.IR groff ,
the GNU
.I roff
text processing system and the classical
.I roff
formatter of the free Unix\~7 of the 1970s, documented in the
.I Troff User's Manual
by
.I Osanna
and
.IR Kernighan .
.
.P
The section
.I SEE ALSO
gives pointers to both the classical
.I roff
and the modern
.I groff
documentation.
.
.P
At the moment, this document is the place of the most actual documentation
with the
.I groff
system.
All novelties are first described here and will pervade into the other
documents only at a later stage.
This might be changed in the future.
.
.
.\" --------------------------------------------------------------------
.SH "NEW FEATURES"
.\" --------------------------------------------------------------------
.
In this section, all additional features of
.I groff
compared to the classical Unix\~7
.I troff
are described in detail.
.
.
.\" --------------------------------------------------------------------
.SS Long names
.\" --------------------------------------------------------------------
.
The names of number registers, fonts, strings/\:macros/\:diversions,
special characters, and colors can be of any length.
In escape sequences, additionally to the classical
.BI ( xx
construction for a two character name, you can use
.BI [ xxx ]
for a name of arbitrary length, for example in
.
.TP \w'\ef[xxx]'u+3n
.BI \e[ xxx ]
Print the special character called
.IR xxx .
.
.TP
.BI \ef[ xxx ]
Set font
.IR xxx .
.
.TP
.BI \e*[ xxx ]
Interpolate string
.IR xxx .
.
.TP
.BI \en[ xxx ]
Interpolate number register
.IR xxx .
.
.
.\" --------------------------------------------------------------------
.SS Fractional pointsizes
.\" --------------------------------------------------------------------
.
A
.I scaled point
is equal to
.B 1/sizescale
points, where
.B sizescale
is specified in the
.B DESC
file (1 by default).
There is a new scale indicator
.B z
that has the effect of multiplying by sizescale.
Requests and escape sequences in troff interpret arguments that represent a
pointsize as being in units of scaled points, but they evaluate each such
argument using a default scale indicator of
.BR z .
Arguments treated in this way are the argument to the
.B ps
request, the third argument to the
.B cs
request, the second and fourth arguments to the
.B tkf
request, the argument to the
.B \eH
escape sequence, and those variants of the
.B \es
escape sequence that take a numeric expression as their argument.
.
.P
For example, suppose sizescale is 1000; then a scaled point will be
equivalent to a millipoint; the request
.B .ps\~10.25
is equivalent to
.B .ps\~10.25z
and so sets the pointsize to 10250 scaled points, which is equal to
10.25 points.
.
.P
The number register
.B \en[.s]
returns the pointsize in points as decimal fraction.
There is also a new number register
.B \en[.ps]
that returns the pointsize in scaled points.
.
.P
It would make no sense to use the
.B z
scale indicator in a numeric expression whose default scale indicator was
neither
.B u
nor
.BR z ,
and so
.B troff
disallows this.
Similarly it would make no sense to use a scaling indicator other than
.B z
or
.B u
in a numeric expression whose default scale indicator was
.BR z ,
and so
.B troff
disallows this as well.
.
.P
There is also new scale indicator
.B s
which multiplies by the number of units in a scaled point.
So, for example,
.B \en[.ps]s
is equal to
.BR 1m .
Be sure not to confuse the
.B s
and
.B z
scale indicators.
.
.
.\" --------------------------------------------------------------------
.SS Numeric expressions
.\" --------------------------------------------------------------------
.
Spaces are permitted in a number expression within parentheses.
.
.P
.B M
indicates a scale of 100ths of an em.
.B f
indicates a scale of 65536 units, providing fractions for color
definitions with
.B defcolor
request.
For example, 0.5f = 32768u.
.
.TP
.IB e1 >? e2
The maximum of
.I e1
and
.IR e2 .
.
.TP
.IB e1 <? e2
The minimum of
.I e1
and
.IR e2 .
.
.TP
.BI ( c ; e )
Evaluate
.I e
using
.I c
as the default scaling indicator.
If
.I c
is missing, ignore scaling indicators in the evaluation of
.IR e .
.
.
.\" --------------------------------------------------------------------
.SS New escape sequences
.\" --------------------------------------------------------------------
.
.TP
.BI \eA' anything '
This expands to
.B 1
or
.B 0
resp., depending on whether
.I anything
is or is not acceptable as the name of a string, macro, diversion, number
register, environment, font, or color.
It will return\~\c
.B 0
if
.I anything
is empty.
This is useful if you want to lookup user input in some sort of associative
table.
.
.TP
.BI \eB' anything '
This expands to
.B 1
or
.B 0
resp., depending on whether
.I anything
is or is not a valid numeric expression.
It will return\~\c
.B 0
if
.I anything
is empty.
.
.TP
.BI \eC' xxx '
Typeset character named
.IR xxx .
Normally it is more convenient to use
.BI \e[ xxx ]\fR.
But
.B \eC
has the advantage that it is compatible with recent versions of
.SM UNIX
and is available in compatibility mode.
.
.TP
.B \eE
This is equivalent to an escape character, but it is not interpreted in
copy-mode.
For example, strings to start and end superscripting could be defined like
this
.
.RS
.IP
\&.ds { \ev'\-.3m'\es'\eEn[.s]*6u/10u'
.br
\&.ds } \es0\ev'.3m'
.
.P
The use of
.B \eE
ensures that these definitions will work even if
.B \e*{
gets interpreted in copy-mode (for example, by being used in a macro
argument).
.RE
.
.TP
.BI \em x
.TQ
.BI \em( xx
.TQ
.BI \em[ xxx ]
Set drawing color.
.B \emP
switches back to the previous color.
.
.TP
.BI \eM x
.TQ
.BI \eM( xx
.TQ
.BI \eM[ xxx ]
Set background color for filled objects drawn with the
.BI \eD' .\|.\|. '
commands.
.B \eMP
switches back to the previous color.
.
.TP
.BI \eN' n '
Typeset the character with code
.I n
in the current font.
.I n
can be any integer.
Most devices only have characters with codes between 0 and 255.
If the current font does not contain a character with that code, special
fonts will
.I not
be searched.
The
.B \eN
escape sequence can be conveniently used in conjunction with the
.B char
request, for example
.
.RS
.IP
.B
\&.char \e[phone] \ef(ZD\eN'37'
.RE
.
.IP
The code of each character is given in the fourth column in the font
description file after the
.B charset
command.
It is possible to include unnamed characters in the font description file by
using a name of
.BR \-\-\- ;
the
.B \eN
escape sequence is the only way to use these.
.
.TP
.BI \eO n
Suppressing troff output.
The escapes
.BR \e02 ,
.BR \eO3 ,
.BR \eO4 ,
and
.B \eO5
are intended for internal use by
.BR grohtml .
.
.TP
.B \eO0
Disable any ditroff glyphs from being emitted to the device driver, provided
that the escape occurs at the outer level (see
.B \eO3
and
.BR \eO4 ).
.
.TP
.B \eO1
Enable output of glyphs, provided that the escape occurs at the outer
level.
.IP
.B \eO0
and
.B \eO1
also reset the registers
.BR \en[opminx] ,
.BR \en[opminy] ,
.BR \en[opmaxx] ,
and
.B \en[opmaxy]
to\~-1.
These four registers mark the top left and bottom right hand corners of a
box which encompasses all written glyphs.
.
.TP
.B \eO2
Provided that the escape occurs at the outer level, enable output of glyphs
and also write out to stderr the page number and four registers encompassing
the glyphs previously written since the last call to
.BR \eO .
.
.TP
.B \eO3
Begin a nesting level.
This is really an internal mechanism for
.B grohtml
while producing images.
They are generated by running the troff source through troff to the
postscript device and ghostscript to produce images in PNG format.
The
.B \eO3
escape will start a new page if the device is not html (to reduce the
possibility of images crossing a page boundary).
.
.TP
.B \eO4
End a nesting level.
.TP
.BI \eO5[ Pfilename ]
This escape is
.B grohtml
specific.
Provided that this escape occurs at the outer nesting level, write
.I filename
to stderr.
The position of the image,
.IR P ,
must be specified and must be one of l, r, c or i (left, right, centered,
inline).
.I filename
will be associated with the production of the next inline image.
.
.TP
.BI \eR' name\ \(+-n '
This has the same effect as
.
.RS
.IP
.BI .nr\  name\ \(+-n
.RE
.
.TP
.BI \es( nn
.TQ
.BI \es\(+-( nn
Set the point size to
.I nn
points;
.I nn
must be exactly two digits.
.
.TP
.BI \es[\(+- n ]
.TQ
.BI \es\(+-[ n ]
.TQ
.BI \es'\(+- n '
.TQ
.BI \es\(+-' n '
Set the point size to
.I n
scaled points;
.I n
is a numeric expression with a default scale indicator of\~\c
.BR z .
.
.TP
.BI \eV x
.TQ
.BI \eV( xx
.TQ
.BI \eV[ xxx ]
Interpolate the contents of the environment variable
.IR xxx ,
as returned by
.BR getenv (3).
.B \eV
is interpreted in copy-mode.
.
.TP
.BI \eY x
.TQ
.BI \eY( xx
.TQ
.BI \eY[ xxx ]
This is approximately equivalent to
.BI \eX'\e*[ xxx ]'\fR.
However the contents of the string or macro
.I xxx
are not interpreted; also it is permitted for
.I xxx
to have been defined as a macro and thus contain newlines (it is not
permitted for the argument to
.B \eX
to contain newlines).
The inclusion of newlines requires an extension to the UNIX troff output
format, and will confuse drivers that do not know about this extension.
.
.TP
.BI \eZ' anything '
Print anything and then restore the horizontal and vertical position;
.I anything
may not contain tabs or leaders.
.
.TP
.B \e$0
The name by which the current macro was invoked.
.
The
.B als
request can make a macro have more than one name.
.
.TP
.B \e$*
In a macro, the concatenation of all the arguments separated by spaces.
.
.TP
.B \e$@
In a macro, the concatenation of all the arguments with each surrounded by
double quotes, and separated by spaces.
.
.TP
.BI \e$( nn
.TQ
.BI \e$[ nnn ]
In a macro, this gives the
.IR nn -th
or
.IR nnn -th
argument.
Macros can have an unlimited number of arguments.
.
.TP
.BI \e? anything \e?
When used in a diversion, this will transparently embed
.I anything
in the diversion.
.I anything
is read in copy mode.
When the diversion is reread,
.I anything
will be interpreted.
.I anything
may not contain newlines; use
.B \e!\&
if you want to embed newlines in a diversion.
The escape sequence
.B \e?\&
is also recognised in copy mode and turned into a single internal code; it
is this code that terminates
.IR anything .
Thus
.
.RS
.IP
.NE 14v+\n(.Vu
.ft B
.nf
\&.nr x 1
\&.nf
\&.di d
\e?\e\e?\e\e\e\e?\e\e\e\e\e\e\e\enx\e\e\e\e?\e\e?\e?
\&.di
\&.nr x 2
\&.di e
\&.d
\&.di
\&.nr x 3
\&.di f
\&.e
\&.di
\&.nr x 4
\&.f
.fi
.ft
.RE
.
.IP
will print\~\c
.BR 4 .
.
.TP
.B \e/
This increases the width of the preceding character so that the spacing
between that character and the following character will be correct if the
following character is a roman character.
.if t \{\
.  nop For example, if an italic f is immediately followed by a roman right
.  nop parenthesis, then in many fonts the top right portion of the f will
.  nop overlap the top left of the right parenthesis producing \fIf\fR)\fR,
.  nop which is ugly.
.  nop Inserting
.  B \e/
.  nop produces
.  ie \n(.g \fIf\/\fR)\fR
.  el       \fIf\|\fR)\fR
.  nop and avoids this problem.
.\}
It is a good idea to use this escape sequence whenever an italic character
is immediately followed by a roman character without any intervening space.
.
.TP
.B \e,
This modifies the spacing of the following character so that the spacing
between that character and the preceding character will correct if the
preceding character is a roman character.
.if t \{\
.  nop For example, inserting
.  B \e,
.  nop between the parenthesis and the f changes
.  nop \fR(\fIf\fR to
.  ie \n(.g \fR(\,\fIf\fR.
.  el       \fR(\^\fIf\fR.
.\}
It is a good idea to use this escape sequence whenever a roman
character is immediately followed by an italic character without any
intervening space.
.
.TP
.B \e)
Like
.B \e&
except that it behaves like a character declared with the
.B cflags
request to be transparent for the purposes of end-of-sentence recognition.
.
.TP
.B \e~
This produces an unbreakable space that stretches like a normal inter-word
space when a line is adjusted.
.
.TP
.B \e:
This causes the insertion of a zero-width break point.
It is equal to
.B \e%
but without insertion of a soft hyphen character.
.
.TP
.B \e#
Everything up to and including the next newline is ignored.
This is interpreted in copy mode.
It is like
.B \e"
except that
.B \e"
does not ignore the terminating newline.
.
.
.\" --------------------------------------------------------------------
.SS New requests
.\" --------------------------------------------------------------------
.
.TP
.BI .aln\  xx\ yy
Create an alias
.I xx
for number register object named
.IR yy .
The new name and the old name will be exactly equivalent.
If
.I yy
is undefined, a warning of type
.B reg
will be generated, and the request will be ignored.
.
.TP
.BI .als\  xx\ yy
Create an alias
.I xx
for request, string, macro, or diversion object named
.IR yy .
The new name and the old name will be exactly equivalent (it is similar to a
hard rather than a soft link).
If
.I yy
is undefined, a warning of type
.B mac
will be generated, and the request will be ignored.
The
.BR de ,
.BR am ,
.BR di ,
.BR da ,
.BR ds ,
and
.B as
requests only create a new object if the name of the macro, diversion or
string diversion is currently undefined or if it is defined to be a request;
normally they modify the value of an existing object.
.
.TP
.BI .am1\  xx\ yy
Similar to
.BR .am , 
but compatibility mode is switched off during execution.
On entry, the current compatibility mode is saved and restored at exit.
.
.TP
.BI .asciify\  xx
This request `unformats' the diversion
.I xx
in such a way that
.SM ASCII
and space characters (and some escape sequences) that were formatted and
diverted into
.I xx
will be treated like ordinary input characters when
.I xx
is reread.
Useful for diversions in conjunction with the
.B .writem
request.
It can be also used for gross hacks; for example, this
.
.RS
.IP
.NE 7v+\n(.Vu
.ft B
.nf
\&.tr @.
\&.di x
\&@nr n 1
\&.br
\&.di
\&.tr @@
\&.asciify x
\&.x
.fi
.RE
.
.IP
will set register\~\c
.B n
to\~1.
Note that glyph information (font, font size, etc.) is not preserved; use
.B .unformat
instead.
.
.TP
.B .backtrace
Print a backtrace of the input stack on stderr.
.
.TP
.BI .blm\  xx
Set the blank line macro to
.IR xx .
If there is a blank line macro, it will be invoked when a blank line
is encountered instead of the usual troff behaviour.
.
.TP
.BI .box\  xx
.TQ
.BI .boxa\  xx
These requests are similar to the
.B di
and
.B da
requests with the exception that a partially filled line will not become
part of the diversion (i.e., the diversion always starts with a new line)
but restored after ending the diversion, discarding the partially filled
line which possibly comes from the diversion.
.
.TP
.B .break
Break out of a while loop.
See also the
.B while
and
.B continue
requests.
Be sure not to confuse this with the
.B br
request.
.
.TP
.B .brp
This is the same as
.BR \ep .
.
.TP
.BI .cflags\  n\ c1\ c2\|.\|.\|.
Characters
.IR c1 ,
.IR c2 ,\|.\|.\|.
have properties determined by
.IR n ,
which is ORed from the following:
.
.RS
.IP 1
The character ends sentences (initially characters
.B .?!\&
have this property).
.
.IP 2
Lines can be broken before the character (initially no characters have this
property); a line will not be broken at a character with this property
unless the characters on each side both have non-zero hyphenation codes.
.
.IP 4
Lines can be broken after the character (initially characters
.B \-\e(hy\e(em
have this property); a line will not be broken at a character with this
property unless the characters on each side both have non-zero hyphenation
codes.
.
.IP 8
The character overlaps horizontally (initially characters
.B \e(ul\e(rn\e(ru
have this property);
.
.IP 16
The character overlaps vertically (initially character
.B \e(br
has this property);
.
.IP 32
An end-of-sentence character followed by any number of characters with
this property will be treated as the end of a sentence if followed by
a newline or two spaces; in other words the character is transparent
for the purposes of end-of-sentence recognition; this is the same as
having a zero space factor in \*(tx (initially characters
.B \(dq')]*\e(dg\e(rq
have this property).
.RE
.
.TP
.BI .char\  c\ string
Define character
.I c
to be
.IR string .
Every time character
.I c
needs to be printed,
.I string
will be processed in a temporary environment and the result will be wrapped
up into a single object.
Compatibility mode will be turned off and the escape character will be set
to
.B \e
while
.I string
is being processed.
Any emboldening, constant spacing or track kerning will be applied to this
object rather than to individual characters in
.IR string .
A character defined by this request can be used just like a normal character
provided by the output device.
In particular other characters can be translated to it with the
.B tr
request; it can be made the leader character by the
.B lc
request; repeated patterns can be drawn with the character using the
.B \el
and
.B \eL
escape sequences; words containing the character can be hyphenated
correctly, if the
.B hcode
request is used to give the character a hyphenation code.
There is a special anti-recursion feature: use of character within the
character's definition will be handled like normal characters not defined
with
.BR char .
A character definition can be removed with the
.B rchar
request.
.
.TP
.BI .chop\  xx
Chop the last character off macro, string, or diversion
.IR xx .
This is useful for removing the newline from the end of diversions that are
to be interpolated as strings.
.
.TP
.BI .close\  stream
Close the stream named
.IR stream ;
.I stream
will no longer be an acceptable argument to the
.B write
request.
See the
.B open
request.
.
.TP
.B .continue
Finish the current iteration of a while loop.
See also the
.B while
and
.B break
requests.
.
.TP
.BI .cp\  n
If
.I n
is non-zero or missing, enable compatibility mode, otherwise disable it.
In compatibility mode, long names are not recognised, and the
incompatibilities caused by long names do not arise.
.
.TP
.BI .defcolor\  xxx\ scheme\ color_components
Define color.
.I scheme
can be one of the following values:
.B rgb
(three components),
.B cym
(three components),
.B cmyk
(four components), and
.B gray
or
.B grey
(one component).
.
Color components can be given either as a hexadecimal string or as positive
decimal integers in the range 0-65535.
A hexadecimal string contains all color components concatenated; it must
start with either
.B #
or
.BR ## .
The former specifies hex values in the range 0-255 (which are internally
multiplied by\~257), the latter in the range 0-65535.
Examples: #FFC0CB (pink), ##ffff0000ffff (magenta).
A new scaling indicator\~\c
.B f
has been introduced which multiplies its value by 65536; this makes it
convenient to specify color components as fractions in the range 0 to\~1.
Example:
.
.RS
.IP
.B
\&.defcolor darkgreen rgb 0.1f 0.5f 0.2f
.RE
.
.IP
Note that
.B f
is the default scaling indicator for the
.B defcolor
request, thus the above statement is equivalent to
.
.RS
.IP
.B
\&.defcolor darkgreen rgb 0.1 0.5 0.2
.RE
.
.TP
.BI .dei\  xx\ yy
Define macro indirectly.
.
The following example
.
.RS
.IP
.NE 2v+\n(.Vu
.ft B
.nf
\&.ds xx aa
\&.ds yy bb
\&.dei xx yy
.fi
.RE
.
.IP
is equivalent to
.
.RS
.IP
.B
\&.de aa bb
.RE
.
.TP
.BI .de1\  xx\ yy
Similar to
.BR .de , 
but compatibility mode is switched off during execution.
On entry, the current compatibility mode is saved and restored at exit.
.
.TP
.BI .do\  xxx
Interpret
.I .xxx
with compatibility mode disabled.
For example,
.
.RS
.IP
.B
\&.do fam T
.P
would have the same effect as
.
.IP
.B
\&.fam T
.P
except that it would work even if compatibility mode had been enabled.
Note that the previous compatibility mode is restored before any files
sourced by
.I xxx
are interpreted.
.RE
.
.TP
.B .ecs
Save current escape character.
.
.TP
.B .ecr
Restore escape character saved with
.BR ecs .
Without a previous call to
.BR ecs ,
.RB ` \e '
will be the new escape character.
.
.TP
.BI .evc\  xx
Copy the contents of environment
.I xx
to the current environment.
No pushing or popping of environments will be done.
.
.TP
.BI .fam\  xx
Set the current font family to
.IR xx .
The current font family is part of the current environment.
If
.I xx
is missing, switch back to previous font family.
See the description of the
.B sty
request for more information on font families.
.
.TP
.BI .fspecial\  f\ s1\ s2\|.\|.\|.
When the current font is
.IR f ,
fonts
.IR s1 ,
.IR s2 ,\|.\|.\|.
will be special, that is, they will searched for characters not in the
current font.
Any fonts specified in the
.B special
request will be searched after fonts specified in the
.B fspecial
request.
.
.TP
.BI .ftr\  f\ g
Translate font
.I f
to
.IR g .
Whenever a font named
.I f
is referred to in an
.B \ef
escape sequence, or in the
.BR ft ,
.BR ul ,
.BR bd ,
.BR cs ,
.BR tkf ,
.BR special ,
.BR fspecial ,
.BR fp ,
or
.BR sty
requests, font
.I g
will be used.
If
.I g
is missing, or equal to
.I f
then font
.I f
will not be translated.
.
.TP
.BI .hcode \ c1\ code1\ c2\ code2\|.\|.\|.
Set the hyphenation code of character
.I c1
to
.I code1
and that of
.I c2
to
.IR code2 .
A hyphenation code must be a single input character (not a special
character) other than a digit or a space.
Initially each lower-case letter has a hyphenation code, which is itself,
and each upper-case letter has a hyphenation code which is the lower case
version of itself.
See also the
.B hpf
request.
.
.TP
.BI .hla\  lang
Set the current hyphenation language to
.IR lang .
Hyphenation exceptions specified with the
.B hw
request and hyphenation patterns specified with the
.B hpf
request are both associated with the current hyphenation language.
The
.B hla
request is usually invoked by the
.B troffrc
file.
.
.TP
.BI .hlm\  n
Set the maximum number of consecutive hyphenated lines to\~\c
.IR n .
If
.I n
is negative, there is no maximum.
The default value is\~\-1.
This value is associated with the current environment.
Only lines output from an environment count towards the maximum associated
with that environment.
Hyphens resulting from
.B \e%
are counted; explicit hyphens are not.
.
.TP
.BI .hpf\  file
Read hyphenation patterns from
.IR file ;
this will be searched for in the same way that
.IB name .tmac
is searched for when the
.BI \-m name
option is specified.
It should have the same format as the argument to the \epatterns primitive
in \*(tx; the letters appearing in this file are interpreted as hyphenation
codes.
A
.BR % \~\c
character in the patterns file introduces a comment that continues to the
end of the line.
The set of hyphenation patterns is associated with the current language set
by the
.B hla
request.
The
.B hpf
request is usually invoked by the
.B troffrc
file.
.
.TP
.BI .hym\  n
Set the
.I hyphenation margin
to\~\c
.IR n :
when the current adjustment mode is not\~\c
.BR b ,
the line will not be hyphenated if the line is no more than
.I n
short.
The default hyphenation margin is\~0.
The default scaling indicator for this request is\~\c
.IR m .
The hyphenation margin is associated with the current environment.
The current hyphenation margin is available in the
.B \en[.hym]
register.
.
.TP
.BI .hys\  n
Set the
.I hyphenation space
to\~\c
.IR n :
when the current adjustment mode is\~\c
.B b
don't hyphenate the line if the line can be justified by adding no more than
.I n
extra space to each word space.
The default hyphenation space is\~0.
The default scaling indicator for this request is\~\c
.BR m .
The hyphenation space is associated with the current environment.
The current hyphenation space is available in the
.B \en[.hys]
register.
.
.TP
.BI .kern\  n
If
.I n
is non-zero or missing, enable pairwise kerning, otherwise disable it.
.
.TP
.BI .length\  xx\ string
Compute the length of
.I string
and return it in the number register
.I xx
(which is not necessarily defined before).
.
.TP
.BI .linetabs\  n
If
.I n
is non-zero or missing, enable line-tabs mode, otherwise disable it
(which is the default).
In line-tabs mode, tab distances are computed relative to the (current)
output line.
Otherwise they are taken relative to the input line.
For example, the following
.
.RS
.IP
.NE 6v+\n(.Vu
.ft B
.nf
\&.ds x a\et\ec
\&.ds y b\et\ec
\&.ds z c
\&.ta 1i 3i
\e*x
\e*y
\e*z
.fi
.RE
.
.IP
yields
.
.RS
.IP
a         b         c
.RE
.
.IP
In line-tabs mode, the same code gives
.
.RS
.IP
a         b                   c
.RE
.
.IP
Line-tabs mode is associated with the current environment; the read-only
number register
.B \\en[.linetabs]
is set to\~1 if in line-tabs mode, and 0 otherwise.
.
.TP
.BI .mso\  file
The same as the
.B so
request except that
.I file
is searched for in the same directories as macro files for the the
.B \-m
command line option.
If the file name to be included has the form
.IB name .tmac
and it isn't found,
.B mso
tries to include
.BI tmac. name
instead and vice versa.
.
.TP
.BI .nop \ anything
Execute
.IR anything .
This is similar to `.if\ 1'.
.
.TP
.B .nroff
Make the
.B n
built-in condition true and the
.B t
built-in condition false.
This can be reversed using the
.B troff
request.
.
.TP
.BI .open\  stream\ filename
Open
.I filename
for writing and associate the stream named
.I stream
with it.
See also the
.B close
and
.B write
requests.
.
.TP 
.BI .opena\  stream\ filename
Like
.BR open ,
but if
.I filename
exists, append to it instead of truncating it.
.
.TP
.B .pnr
Print the names and contents of all currently defined number registers on
stderr.
.
.TP
.BI .psbb \ filename
Get the bounding box of a PostScript image
.IR filename .
This file must conform to Adobe's Document Structuring Conventions; the
command looks for a
.B \%%%BoundingBox
comment to extract the bounding box values.
After a successful call, the coordinates (in PostScript units) of the lower
left and upper right corner can be found in the registers
.BR \en[llx] ,
.BR \en[lly] ,
.BR \en[urx] ,
and
.BR \en[ury] ,
respectively.
If some error has occurred, the four registers are set to zero.
.
.TP
.BI .pso \ command
This behaves like the
.B so
request except that input comes from the standard output of
.IR command .
.
.TP
.B .ptr
Print the names and positions of all traps (not including input line
traps and diversion traps) on stderr.
.
Empty slots in the page trap list are printed as well, because they
can affect the priority of subsequently planted traps.
.
.TP
.BI .rchar\  c1\ c2\|.\|.\|.
Remove the definitions of characters
.IR c1 ,
.IR c2 ,\|.\|.\|.
This undoes the effect of a
.B char
request.
.
.TP
.B .return
Within a macro, return immediately.
No effect otherwise.
.
.TP
.B .rj
.TQ
.BI .rj\  n
Right justify the next
.IR n \~\c
input lines.
Without an argument right justify the next input line.
The number of lines to be right justified is available in the
.B \en[.rj]
register.
This implicitly does
.BR .ce \~0 .
The
.B ce
request implicitly does
.BR .rj \~0 .
.
.TP
.BI .rnn \ xx\ yy
Rename number register
.I xx
to
.IR yy .
.
.TP
.BI .shc\  c
Set the soft hyphen character to
.IR c .
If
.I c
is omitted, the soft hyphen character will be set to the default
.BR \e(hy .
The soft hyphen character is the character which will be inserted when a
word is hyphenated at a line break.
If the soft hyphen character does not exist in the font of the character
immediately preceding a potential break point, then the line will not be
broken at that point.
Neither definitions (specified with the
.B char
request) nor translations (specified with the
.B tr
request) are considered when finding the soft hyphen character.
.
.TP
.BI .shift\  n
In a macro, shift the arguments by
.I n
positions: argument\~\c
.I i
becomes argument
.IR i \- n ;
arguments 1 to\~\c
.I n
will no longer be available.
If
.I n
is missing, arguments will be shifted by\~1.
Shifting by negative amounts is currently undefined.
.
.TP
.BI .special\  s1\ s2\|.\|.\|.
Fonts
.IR s1 ,
.IR s2 ,
are special and will be searched for characters not in the current
font.
.
.TP
.BI .sty\  n\ f
Associate style\~\c
.I f
with font position\~\c
.IR n .
A font position can be associated either with a font or with a style.
The current font is the index of a font position and so is also either a
font or a style.
When it is a style, the font that is actually used is the font the name of
which is the concatenation of the name of the current family and the name of
the current style.
For example, if the current font is\~1 and font position\~1 is associated
with style
.B R
and the current font family is\~\c
.BR T ,
then font
.BR TR
will be used.
If the current font is not a style, then the current family is ignored.
When the requests
.BR cs ,
.BR bd ,
.BR tkf ,
.BR uf ,
or
.B fspecial
are applied to a style, then they will instead be applied to the member of
the current family corresponding to that style.
The default family can be set with the
.B \-f
option.
The styles command in the
.SM DESC
file controls which font positions (if any) are initially associated
with styles rather than fonts.
.
.TP
.BI .substring\  xx\ n1\  [ n2 ]
Replace the string in register
.I xx
with the substring defined by the indices
.I n1
and
.IR n2 .
The first character in the string has index one.
If
.I n2
is omitted, it is taken to be equal to the string's length.
If the index value
.I n1
or
.I n2
is negative or zero, it will be counted from the end of the string, going
backwards:
The last character has index\~0, the character before the last character has
index\~-1, etc.
.
.TP
.BI .tkf\  f\ s1\ n1\ s2\ n2
Enable track kerning for font
.IR f .
When the current font is
.I f
the width of every character will be increased by an amount between
.I n1
and
.IR n2 ;
when the current point size is less than or equal to
.I s1
the width will be increased by
.IR n1 ;
when it is greater than or equal to
.I s2
the width will be increased by
.IR n2 ;
when the point size is greater than or equal to
.I s1
and less than or equal to
.I s2
the increase in width is a linear function of the point size.
.
.TP
.BI .tm1\  string
Similar to the
.B tm
request,
.I string
is read in copy mode and written on the standard error, but an initial
double quote in
.I string
is stripped off to allow initial blanks.
.
.TP
.BI .tmc\  string
Similar to
.BR tm1
but without writing a final newline.
.
.TP
.BI .trf\  filename
Transparently output the contents of file
.IR filename .
Each line is output as it would be preceded by
.BR \e! ;
however, the lines are not subject to copy-mode interpretation.
If the file does not end with a newline, then a newline will be added.
For example, you can define a macro\~\c
.I x
containing the contents of file\~\c
.IR f ,
using
.
.RS
.IP
.NE 2v+\n(.Vu
.ft B
.nf
\&.di x
\&.trf f
\&.di
.fi
.RE
.
.IP
Unlike with the
.B cf
request, the file cannot contain characters such as
.SM NUL
that are not legal troff input characters.
.
.TP
.B .trnt abcd
This is the same as the
.B tr
request except that the translations do not apply to text that is
transparently throughput into a diversion with
.BR \e! .
For example,
.
.RS
.IP
.nf
.ft B
\&.tr ab
\&.di x
\e!.tm a
\&.di
\&.x
.fi
.ft
.RE
.
.IP
will print\~\c
.BR b ;
if
.B trnt
is used instead of
.B tr
it will print\~\c
.BR a .
.
.TP
.B .troff
Make the
.B n
built-in condition false, and the
.B t
built-in condition true.
This undoes the effect of the
.B nroff
request.
.
.TP
.BI .unformat\  xx
This request `unformats' the diversion
.IR xx .
Contrary to the
.B .asciify
request, which tries to convert formatted elements of the diversion back to
input tokens as much as possible,
.B .unformat
will only handle tabs and spaces between words (usually caused by spaces or
newlines in the input) specially.
The former are treated as if they were input tokens, and the latter are
stretchable again.
Note that the vertical size of lines is not preserved.
Glyph information (font, font size, space width, etc.) is retained.
Useful in conjunction with the
.B .box
and
.B .boxa
requests.
.
.TP
.BI .vpt\  n
Enable vertical position traps if
.I n
is non-zero, disable them otherwise.
Vertical position traps are traps set by the
.B wh
or
.B dt
requests.
Traps set by the
.B it
request are not vertical position traps.
The parameter that controls whether vertical position traps are enabled is
global.
Initially vertical position traps are enabled.
.
.TP
.BI .warn\  n
Control warnings.
.I n
is the sum of the numbers associated with each warning that is to be
enabled; all other warnings will be disabled.
The number associated with each warning is listed in the `Warnings' section.
For example,
.B .warn\~0
will disable all warnings, and
.B .warn\~1
will disable all warnings except that about missing characters.
If
.I n
is not given, all warnings will be enabled.
.
.TP
.BI .while \ c\ anything
While condition\~\c
.I c
is true, accept
.I anything
as input;
.IR c \~\c
can be any condition acceptable to an
.B if
request;
.I anything
can comprise multiple lines if the first line starts with
.B \e{
and the last line ends with
.BR \e} .
See also the
.B break
and
.B continue
requests.
.
.TP
.BI .write\  stream\ anything
Write
.I anything
to the stream named
.IR stream .
.I stream
must previously have been the subject of an
.B open
request.
.I anything
is read in copy mode;
a leading\~\c
.B \(dq
will be stripped.
.
.TP
.BI .writem\  stream\ xx
Write the contents of the macro or string
.I xx
to the stream named
.IR stream .
.I stream
must previously have been the subject of an
.B open
request.
.I xx
is read in copy mode.
.
.
.\" --------------------------------------------------------------------
.SS Extended requests
.\" --------------------------------------------------------------------
.
.TP
.BI .cf\  filename
When used in a diversion, this will embed in the diversion an object which,
when reread, will cause the contents of
.I filename
to be transparently copied through to the output.
.
In UNIX troff, the contents of
.I filename
is immediately copied through to the output regardless of whether there is a
current diversion; this behaviour is so anomalous that it must be considered
a bug.
.
.TP
.BI .ev\  xx
If
.I xx
is not a number, this will switch to a named environment called
.IR xx .
The environment should be popped with a matching
.B ev
request without any arguments, just as for numbered environments.
There is no limit on the number of named environments; they will be created
the first time that they are referenced.
.
.TP
.BI .fp\  n\ f1\ f2
The
.B fp
request has an optional third argument.
This argument gives the external name of the font, which is used for finding
the font description file.
The second argument gives the internal name of the font which is used to
refer to the font in troff after it has been mounted.
If there is no third argument then the internal name will be used as the
external name.
This feature allows you to use fonts with long names in compatibility mode.
.
.TP
.BI .ss\  m\ n
When two arguments are given to the
.B ss
request, the second argument gives the
.IR "sentence space size" .
If the second argument is not given, the sentence space size will be the
same as the word space size.
Like the word space size, the sentence space is in units of one twelfth of
the spacewidth parameter for the current font.
Initially both the word space size and the sentence space size are\~12.
Contrary to UNIX troff, GNU troff handles this request in nroff mode also; a
given value is then rounded down to the nearest multiple of\~12.
The sentence space size is used in two circumstances:
If the end of a sentence occurs at the end of a line in fill mode, then both
an inter-word space and a sentence space will be added; if two spaces follow
the end of a sentence in the middle of a line, then the second space will be
a sentence space.
Note that the behaviour of UNIX troff will be exactly that exhibited by GNU
troff if a second argument is never given to the
.B ss
request.
In GNU troff, as in UNIX troff, you should always follow a sentence with
either a newline or two spaces.
.
.TP
.BI .ta\  n1\ n2\|.\|.\|.nn \ T\  r1\ r2\|.\|.\|.\|rn
Set tabs at positions
.IR n1 ,
.IR n2 ,\|.\|.\|.\|,
.I nn
and then set tabs at
.IR nn + r1 ,
.IR nn + r2 ,\|.\|.\|.\|.\|,
.IR nn + rn
and then at
.IR nn + rn + r1 ,
.IR nn + rn + r2 ,\|.\|.\|.\|,
.IR nn + rn + rn ,
and so on.
For example,
.
.RS
.IP
.B
\&.ta T .5i
.P
will set tabs every half an inch.
.RE
.
.
.\" --------------------------------------------------------------------
.SS New number registers
.\" --------------------------------------------------------------------
.
The following read-only registers are available:
.
.TP
.B \en[.C]
1\~if compatibility mode is in effect, 0\~otherwise.
.
.TP
.B \en[.cdp]
The depth of the last character added to the current environment.
It is positive if the character extends below the baseline.
.
.TP
.B \en[.ce]
The number of lines remaining to be centered, as set by the
.B ce
request.
.
.TP
.B \en[.cht]
The height of the last character added to the current environment.
It is positive if the character extends above the baseline.
.
.TP
.B \en[.csk]
The skew of the last character added to the current environment.
The
.I skew
of a character is how far to the right of the center of a character the
center of an accent over that character should be placed.
.
.TP
.B \en[.ev]
The name or number of the current environment.
This is a string-valued register.
.
.TP
.B \en[.fam]
The current font family.
This is a string-valued register.
.
.TP
.B \en[.fp]
The number of the next free font position.
.
.TP
.B \en[.g]
Always\~1.
Macros should use this to determine whether they are running under GNU
troff.
.
.TP
.B \en[.hla]
The current hyphenation language as set by the
.B hla
request.
.
.TP
.B \en[.hlc]
The number of immediately preceding consecutive hyphenated lines.
.
.TP
.B \en[.hlm]
The maximum allowed number of consecutive hyphenated lines, as set by the
.B hlm
request.
.
.TP
.B \en[.hy]
The current hyphenation flags (as set by the
.B hy
request).
.
.TP
.B \en[.hym]
The current hyphenation margin (as set by the
.B hym
request).
.
.TP
.B \en[.hys]
The current hyphenation space (as set by the
.B hys
request).
.
.TP
.B \en[.in]
The indent that applies to the current output line.
.
.TP
.B \en[.int]
Set to a positive value if last output line is interrupted (i.e., if
it contains
.IR \ec ).
.
.TP
.B \en[.kern]
1\~if pairwise kerning is enabled, 0\~otherwise.
.
.TP
.B \en[.lg]
The current ligature mode (as set by the
.B lg
request).
.
.TP
.B \en[.linetabs]
The current line-tabs mode (as set by the
.B linetabs
request).
.
.TP
.B \en[.ll]
The line length that applies to the current output line.
.
.TP
.B \en[.lt]
The title length as set by the
.B lt
request.
.
.TP
.B \en[.ne]
The amount of space that was needed in the last
.B ne
request that caused a trap to be sprung.
Useful in conjunction with the
.B \en[.trunc]
register.
.
.TP
.B \en[.ns]
1\~if no-space mode is active, 0\~otherwise.
.
.TP
.B \en[.pn]
The number of the next page, either the value set by a
.B pn
request, or the number of the current page plus\~1.
.
.TP
.B \en[.ps]
The current pointsize in scaled points.
.
.TP
.B \en[.psr]
The last-requested pointsize in scaled points.
.
.TP
.B \en[.rj]
The number of lines to be right-justified as set by the
.B rj
request.
.
.TP
.B \en[.sr]
The last requested pointsize in points as a decimal fraction.
This is a string-valued register.
.
.TP
.B \en[.tabs]
A string representation of the current tab settings suitable for use as an
argument to the
.B ta
request.
.
.TP
.B \en[.trunc]
The amount of vertical space truncated by the most recently sprung vertical
position trap, or, if the trap was sprung by a
.B ne
request, minus the amount of vertical motion produced by the
.B ne
request.
In other words, at the point a trap is sprung, it represents the difference
of what the vertical position would have been but for the trap, and what the
vertical position actually is.
Useful in conjunction with the
.B \en[.ne]
register.
.
.TP
.B \en[.ss]
.TQ
.B \en[.sss]
These give the values of the parameters set by the first and second
arguments of the
.B ss
request.
.
.TP
.B \en[.vpt]
1\~if vertical position traps are enabled, 0\~otherwise.
.
.TP
.B \en[.warn]
The sum of the numbers associated with each of the currently enabled
warnings.
The number associated with each warning is listed in the `Warnings'
subsection.
.
.TP
.B \en[.x]
The major version number.
For example, if the version number is 1.03, then
.B \en[.x]
will contain\~1.
.
.TP
.B \en[.y]
The minor version number.
For example, if the version number is 1.03, then
.B \en[.y]
will contain\~03.
.
.TP
.B \en[.Y]
The revision number of groff.
.
.TP
.B \en[llx]
.TQ
.B \en[lly]
.TQ
.B \en[urx]
.TQ
.B \en[ury]
These four registers are set by the
.B \&.psbb
request and contain the bounding box values (in PostScript units) of a given
PostScript image.
.
.P
The following read/write registers are set by the
.B \ew
escape sequence:
.
.TP
.B \en[rst]
.TQ
.B \en[rsb]
Like the
.B st
and
.B sb
registers, but take account of the heights and depths of characters.
.
.TP
.B \en[ssc]
The amount of horizontal space (possibly negative) that should be added to
the last character before a subscript.
.
.TP
.B \en[skw]
How far to right of the center of the last character in the
.B \ew
argument, the center of an accent from a roman font should be placed
over that character.
.
.P
Other available read/write number registers are:
.
.TP
.B \en[c.]
The current input line number.
.B \en[.c]
is a read-only alias to this register.
.
.TP
.B \en[hp]
The current horizontal position at input line.
.
.TP
.B \en[systat]
The return value of the system() function executed by the last
.B sy
request.
.
.TP
.B \en[slimit]
If greater than\~0, the maximum number of objects on the input stack.
If less than or equal to\~0, there is no limit on the number of objects on
the input stack.
With no limit, recursion can continue until virtual memory is exhausted.
.
.TP
.B \en[year]
The current year.
.
Note that the traditional
.B troff
number register
.B \en[yr]
is the current year minus 1900.
.
.
.\" --------------------------------------------------------------------
.SS Miscellaneous
.\" --------------------------------------------------------------------
.
.B @g@troff
predefines a single (read/write) string-based register,
.BR \e*(.T ,
which contains the argument given to the
.B -T
command line option, namely the current output device (for example,
.I latin1
or
.IR ascii ).
Note that this is not the same as the (read-only) number register
.B \en[.T]
which is defined to be\~1 if
.B troff
is called with the
.B -T
command line option, and zero otherwise.
This behaviour is different to UNIX troff.
.
.P
Fonts not listed in the
.SM DESC
file are automatically mounted on the next available font position when they
are referenced.
If a font is to be mounted explicitly with the
.B fp
request on an unused font position, it should be mounted on the first unused
font position, which can be found in the
.B \en[.fp]
register; although
.B troff
does not enforce this strictly, it will not allow a font to be mounted at a
position whose number is much greater than that of any currently used
position.
.
.P
Interpolating a string does not hide existing macro arguments.
Thus in a macro, a more efficient way of doing
.
.IP
.BI . xx\  \e\e$@
.P
is
.
.IP
.BI \e\e*[ xx ]\e\e  
.
.P
If the font description file contains pairwise kerning information,
characters from that font will be kerned.
Kerning between two characters can be inhibited by placing a
.B \e&
between them.
.
.P
In a string comparison in a condition, characters that appear at different
input levels to the first delimiter character will not be recognised as the
second or third delimiters.
This applies also to the
.B tl
request.
In a
.B \ew
escape sequence, a character that appears at a different input level to the
starting delimiter character will not be recognised as the closing delimiter
character.
When decoding a macro argument that is delimited by double quotes, a
character that appears at a different input level to the starting delimiter
character will not be recognised as the closing delimiter character.
The implementation of
.B \e$@
ensures that the double quotes surrounding an argument will appear the same
input level, which will be different to the input level of the argument
itself.
In a long escape name
.B ]
will not be recognized as a closing delimiter except when it occurs at the
same input level as the opening
.BR ] .
In compatibility mode, no attention is paid to the input-level.
.
.P
There are some new types of condition:
.
.TP
.BI .if\ r xxx
True if there is a number register named
.IR xxx .
.
.TP
.BI .if\ d xxx
True if there is a string, macro, diversion, or request named
.IR xxx .
.
.TP
.BI .if\ m xxx
True if there is a color named
.IR xxx .
.
.TP
.BI .if\ c ch
True if there is a character
.IR ch
available;
.I ch
is either an
.SM ASCII
character or a special character
.BI \e( xx
or
.BI \e[ xxx ]\fR;
the condition will also be true if
.I ch
has been defined by the
.B char
request.
.
.P
The
.B tr
request can now map characters onto
.BR \e~ .
.
.P
It is now possible to have whitespace between the first and second dot (or
the name of the ending macro) to end a macro definition.
Example:
.
.IP
.NE 6v+\n(.Vu
.ft B
.nf
\&.de foo
\&.  nop Hello, I'm `foo'.
\&.  nop I will now define `bar'.
\&.  de bar
\&.    nop Hello, I'm `bar'.
\&.  .
\&..
.fi
.
.
.\" --------------------------------------------------------------------
.SH Incompatibilities
.\" --------------------------------------------------------------------
.
Long names cause some incompatibilities.
.
UNIX troff will interpret
.
.IP
.B
\&.dsabcd
.
.P
as defining a string
.B ab
with contents
.BR cd .
Normally, GNU troff will interpret this as a call of a macro named
.BR dsabcd .
Also UNIX troff will interpret
.B \e*[
or
.B \en[
as references to a string or number register called
.BR [ .
In GNU troff, however, this will normally be interpreted as the start of a
long name.
In
.I compatibility mode
GNU troff will interpret these things in the traditional way.
In compatibility mode, however, long names are not recognised.
Compatibility mode can be turned on with the
.B \-C
command line option, and turned on or off with the
.B cp
request.
The number register
.B \en[.C]
is\~1 if compatibility mode is on, 0\~otherwise.
.
.P
GNU troff does not allow the use of the escape sequences
.BR \e\e\e|\e^\e&\e}\e{\e (space) \e'\e`\e-\e_\e!\e%\ec
in names of strings, macros, diversions, number registers, fonts or
environments; UNIX troff does.
The
.B \eA
escape sequence may be helpful in avoiding use of these escape sequences in
names.
.
.P
Fractional pointsizes cause one noteworthy incompatibility.
In UNIX troff the
.B ps 
request ignores scale indicators and so
.
.IP
.B .ps\ 10u
.
.P
will set the pointsize to 10 points, whereas in GNU troff it will set the
pointsize to 10 scaled points.
.
.P
In GNU troff there is a fundamental difference between unformatted, input
characters, and formatted, output characters.
Everything that affects how an output character will be output is stored
with the character; once an output character has been constructed it is
unaffected by any subsequent requests that are executed, including
.BR bd ,
.BR cs ,
.BR tkf ,
.BR tr ,
or
.B fp
requests.
Normally output characters are constructed from input characters at the
moment immediately before the character is added to the current output line.
Macros, diversions and strings are all, in fact, the same type of object;
they contain lists of input characters and output characters in any
combination.
An output character does not behave like an input character for the purposes
of macro processing; it does not inherit any of the special properties that
the input character from which it was constructed might have had.
For example,
.
.IP
.NE 4v+\n(.Vu
.ft B
.nf
\&.di x
\e\e\e\e
\&.br
\&.di
\&.x
.ft
.fi
.
.P
will print
.B \e\e
in GNU troff; each pair of input
.BR \e s
is turned into one output
.B \e
and the resulting output
.BR \e s
are not interpreted as escape characters when they are reread.
UNIX troff would interpret them as escape characters when they were reread
and would end up printing one
.BR \e .
The correct way to obtain a printable
.B \e
is to use the
.B \ee
escape sequence: this will always print a single instance of the current
escape character, regardless of whether or not it is used in a diversion; it
will also work in both GNU troff and UNIX troff.
If you wish for some reason to store in a diversion an escape sequence that
will be interpreted when the diversion is reread, you can either use the
traditional
.B \e!\&
transparent output facility, or, if this is unsuitable, the new
.B \e?\&
escape sequence.
.
.
.\" --------------------------------------------------------------------
.SH AUTHOR
.\" --------------------------------------------------------------------
.
Copyright (C) 1989, 2001 Free Software Foundation, Inc.
.
.P
This document is distributed under the terms of the FDL (GNU Free
Documentation License) version 1.1 or later.
.
You should have received a copy of the FDL on your system, it is also
available on-line at the
.URL "GNU copyleft site" http://\:www.gnu.org/\:copyleft/\:fdl.html .
.
This document was written by James Clark, with modifications by
.URL "Werner Lemberg" mailto:wl@gnu.org
and
.URL "Bernd Warken" mailto:bwarken@mayn.de
.
.P
This document is part of
.IR groff ,
the GNU roff distribution.
Formerly, the informations of this document were kept in the manual page
.BR troff (@MAN1EXT@).
Only the parts dealing with the language aspects of the different
.I roff
systems were carried over into this document.
The
.I troff
command line options and warnings are still available in
.BR @g@troff (@MAN1EXT@).
.
.
.\" --------------------------------------------------------------------
.SH "SEE ALSO"
.\" --------------------------------------------------------------------
.
.TP
.BR roff (@MAN7EXT@)
An overview over
.I groff
and other
.I roff
systems, including pointers to further related documentation.
.
.TP
.BR groff (@MAN7EXT@)
A description of the
.I groff
language, including a short, but complete reference of all predefined
requests, registers, and escapes of plain
.IR groff .
From the command line, this is called by
.BR man\~7\~groff .
.
.P
The
.I groff info
.IR file ,
cf.\&
.BR info (@MAN1EXT@),
presents all groff documentation within a single document.
.
.P
The classical
.I troff
documentation is available on-line at
.URL "Bell Labs CSTR site" http://\:cm.bell-labs.com/\:cm/\:cs/\:cstr.html .
This includes as
.I CSTR #54
the
.I Nroff/\:Troff User's Manual
by
.I J. F. Osanna
of 1976 in the revision of
.I Brian Kernighan
of 1992, being the
.URL "classical troff documentation" \
http://\:cm.bell-labs.com/\:cm/\:cs/\:cstr/\:54.ps.gz .
.
.
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