'\" e
.\" The above line should force the use of eqn as a preprocessor
.TH GROFF_DIFF 7 "7 November 2018" "Groff Version 1.22.3"
.SH NAME
groff_diff \- differences between GNU troff and classical troff
.
.\" groff_diff.man:
.\" Source file position: <groff_source>/man/groff_diff.man
.\" Installed position: <prefix>/share/man/man7/groff_diff.7
.
.
.de co
Copyright \[co] 1989-2014 Free Software Foundation, Inc.
.
.P
This file is part of groff, the GNU roff type-setting system.
.
It is the source of the man-page groff_diff(7).
.P
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
Front-Cover Texts, and with no Back-Cover Texts.
.P
A copy of the Free Documentation License is included as a file called
FDL in the main directory of the groff source package, it is also
available in the internet at
.UR http://\:www.gnu.org/\:copyleft/\:fdl.html
GNU FDL license
.UE .
..
.
.de au
This document was written by
.MT jjc@jclark.com
James Clark
.ME ,
was modified by
.MT wl@gnu.org
Werner Lemberg
.ME
and
.MT groff-bernd.warken-72@web.de
Bernd Warken
.ME .
..
.
.
.\" --------------------------------------------------------------------
.\" Local definitions
.\" --------------------------------------------------------------------
.
.\" define a string tx for the TeX logo
.ie t .ds tx T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X
.el   .ds tx TeX
.
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.
.\" ellipsis
.ds ellipsis \&.\|.\|.\&
.
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.\" --------------------------------------------------------------------
.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 freely available Unix\~7 of the 1970s, documented in
the
.I Troff User\[aq]s Manual
by
.I Ossanna
and
.IR Kernighan .
.
This includes the roff language as well as the intermediate output
format (troff output).
.
.
.P
The section
.I SEE ALSO
gives pointers to both the classical
.I roff
and the modern
.I groff
documentation.
.
.
.\" --------------------------------------------------------------------
.SH "GROFF LANGUAGE"
.\" --------------------------------------------------------------------
.
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 (glyphs), and colors can be of any length.
.
In escape sequences, additionally to the classical
\[oq]\fB(\fP\fIxx\fP\[cq] construction for a two-character glyph name,
you can use \[oq]\fB[\fP\,\fIxxx\/\fP\fB]\fP\[cq] for a name of
arbitrary length.
.
.TP
.BI \[rs][ xxx ]
Print the special character (glyph) called
.IR xxx .
.
.TP
.BI \[rs][ "comp1 comp2 \*[ellipsis]" ]
Print composite glyph consisting of multiple components.
.
Example: \[oq]\[rs][A\~ho]\[cq] is capital letter A with ogonek which
finally maps to glyph name \[oq]u0041_0328\[cq].
.
See the
.I groff info file
for details how a glyph name for a composite glyph is constructed, and
.BR groff_char (7)
for a list of glyph name components used in composite glyph names.
.
.TP
.BI \[rs]f[ xxx ]
Set font
.IR xxx .
.
Additionally,
.B \[rs]f[]
is a new syntax form equal to
.BR \[rs]fP ,
i.e., to return to the previous font.
.
.TP
.BI \[rs]*[ "xxx arg1 arg2 \*[ellipsis]" ]
Interpolate string
.IR xxx ,
taking
.IR arg1 ,
.IR arg2 ,
.IR \*[ellipsis] ,
as arguments.
.
.TP
.BI \[rs]n[ xxx ]
Interpolate number register
.IR xxx .
.
.
.\" --------------------------------------------------------------------
.SS "Fractional point sizes"
.\" --------------------------------------------------------------------
.
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\~\c
.B z
that has the effect of multiplying by sizescale.
.
Requests and escape sequences in troff interpret arguments that
represent a point size as being in units of scaled points, but they
evaluate each such argument using a default scale indicator of\~\c
.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 \[rs]H
escape sequence, and those variants of the
.B \[rs]s
escape sequence that take a numeric expression as their argument.
.
.
.P
For example, suppose sizescale is 1000; then a scaled point is
equivalent to a millipoint; the call
.B .ps\ 10.25
is equivalent to
.B .ps\ 10.25z
and so sets the point size to 10250 scaled points, which is equal to
10.25 points.
.
.
.P
The number register
.B \[rs]n[.s]
returns the point size in points as decimal fraction.
.
There is also a new number register
.B \[rs]n[.ps]
that returns the point size in scaled points.
.
.
.P
It would make no sense to use the
.BR z \~\c
scale indicator in a numeric expression whose default scale indicator
was neither
.B u
nor\~\c
.BR z ,
and so
.B troff
disallows this.
.
Similarly it would make no sense to use a scaling indicator other than
.B z
or\~\c
.B u
in a numeric expression whose default scale indicator was\~\c
.BR z ,
and so
.B troff
disallows this as well.
.
.P
There is also new scale indicator\~\c
.B s
which multiplies by the number of units in a scaled point.
.
So, for example,
.B \[rs]n[.ps]s
is equal to
.BR 1m .
Be sure not to confuse the
.B s
and
.BR z \~\c
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 the
.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\~\c
.IR e .
.
.
.\" --------------------------------------------------------------------
.SS "New escape sequences"
.\" --------------------------------------------------------------------
.
.TP
.BI \[rs]A' anything '
This expands to
.B 1
or\~\c
.BR 0 ,
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 returns\~\c
.B 0
if
.I anything
is empty.
.
This is useful if you want to look up user input in some sort of
associative table.
.
.TP
.BI \[rs]B' anything '
This expands to
.B 1
or\~\c
.BR 0 ,
depending on whether
.I anything
is or is not a valid numeric expression.
.
It returns\~\c
.B 0
if
.I anything
is empty.
.
.TP
.BI \[rs]C' xxx '
Typeset glyph named
.IR xxx .
Normally it is more convenient to use
.BI \[rs][ xxx ]\f[R].
But
.B \[rs]C
has the advantage that it is compatible with recent versions of
.SM UNIX
and is available in compatibility mode.
.
.TP
.B \[rs]E
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
.EX
\&.ds { \[rs]v'\-.3m'\[rs]s'\[rs]En[.s]*6u/10u'
\&.ds } \[rs]s0\[rs]v'.3m'
.EE
.RE
.
.IP
The use of
.B \[rs]E
ensures that these definitions work even if
.B \[rs]*{
gets interpreted in copy mode (for example, by being used in a macro
argument).
.RE
.
.TP
.BI \[rs]F f
.TQ
.BI \[rs]F( fm
.TQ
.BI \[rs]F[ fam ]
Change font family.
.
This is the same as the
.B fam
request.
.
.B \[rs]F[]
switches back to the previous font family (note that
.B \[rs]FP
won\[aq]t work; it selects font family \[oq]P\[cq] instead).
.
.TP
.BI \[rs]m x
.TQ
.BI \[rs]m( xx
.TQ
.BI \[rs]m[ xxx ]
Set drawing color.
.B \[rs]m[]
switches back to the previous color.
.
.TP
.BI \[rs]M x
.TQ
.BI \[rs]M( xx
.TQ
.BI \[rs]M[ xxx ]
Set background color for filled objects drawn with the
.BI \[rs]D' \*[ellipsis] '
commands.
.B \[rs]M[]
switches back to the previous color.
.
.TP
.BI \[rs]N' n '
Typeset the glyph with index\~\c
.I n
in the current font.
.IR n \~\c
can be any integer.
.
Most devices only have glyphs with indices between 0 and 255.
.
If the current font does not contain a glyph with that code,
special fonts are
.I not
searched.
.
The
.B \[rs]N
escape sequence can be conveniently used in conjunction with the
.B char
request, for example
.
.RS
.IP
.EX
\&.char \[rs][phone] \[rs]f(ZD\[rs]N'37'
.EE
.RE
.
.IP
The index of each glyph is given in the fourth column in the font
description file after the
.B charset
command.
.
It is possible to include unnamed glyphs in the font description
file by using a name of
.BR \-\-\- ;
the
.B \[rs]N
escape sequence is the only way to use these.
.
.TP
.BI \[rs]O n
.TQ
.BI \[rs]O[ n ]
Suppress troff output.
.
The escapes
.BR \[rs]O2 ,
.BR \[rs]O3 ,
.BR \[rs]O4 ,
and
.B \[rs]O5
are intended for internal use by
.BR \%grohtml .
.
.RS
.TP
.B \[rs]O0
Disable any ditroff glyphs from being emitted to the device driver,
provided that the escape occurs at the outer level (see
.B \[rs]O3
and
.BR \[rs]O4 ).
.
.TP
.B \[rs]O1
Enable output of glyphs, provided that the escape occurs at the outer
level.
.IP
.B \[rs]O0
and
.B \[rs]O1
also reset the registers
.BR \[rs]n[opminx] ,
.BR \[rs]n[opminy] ,
.BR \[rs]n[opmaxx] ,
and
.B \[rs]n[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 \[rs]O2
Provided that the escape occurs at the outer level, enable output of
glyphs and also write out to stderr the page number and four registers
encompassing the glyphs previously written since the last call to
.BR \[rs]O .
.
.TP
.B \[rs]O3
Begin a nesting level.
.
At start-up,
.B troff
is at outer level.
.
This is really an internal mechanism for
.B \%grohtml
while producing images.
.
They are generated by running the troff source through
.B troff
to the postscript device and
.B ghostscript
to produce images in PNG format.
.
The
.B \[rs]O3
escape starts a new page if the device is not html (to reduce the
possibility of images crossing a page boundary).
.
.TP
.B \[rs]O4
End a nesting level.
.
.TP
.BI \[rs]O5[ 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
.BR l ,
.BR r ,
.BR c ,
or
.B i
(left, right, centered, inline).
.
.I filename
is associated with the production of the next inline image.
.RE
.
.TP
.BI \[rs]R' name\ \[+-]n '
This has the same effect as
.
.RS
.IP
.BI .nr\  name\ \[+-]n
.RE
.
.TP
.BI \[rs]s( nn
.TQ
.BI \[rs]s\[+-]( nn
Set the point size to
.I nn
points;
.I nn
must be exactly two digits.
.
.TP
.BI \[rs]s[\[+-] n ]
.TQ
.BI \[rs]s\[+-][ n ]
.TQ
.BI \[rs]s'\[+-] n '
.TQ
.BI \[rs]s\[+-]' 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 \[rs]V x
.TQ
.BI \[rs]V( xx
.TQ
.BI \[rs]V[ xxx ]
Interpolate the contents of the environment variable
.IR xxx ,
as returned by
.BR getenv (3).
.B \[rs]V
is interpreted in copy mode.
.
.TP
.BI \[rs]Y x
.TQ
.BI \[rs]Y( xx
.TQ
.BI \[rs]Y[ xxx ]
This is approximately equivalent to
.BI \[rs]X'\[rs]*[ xxx ]'\f[R].
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 \[rs]X
to contain newlines).
.
The inclusion of newlines requires an extension to the UNIX troff
output format, and confuses drivers that do not know about this
extension.
.
.TP
.BI \[rs]Z' anything '
Print anything and then restore the horizontal and vertical position;
.I anything
may not contain tabs or leaders.
.
.TP
.B \[rs]$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 \[rs]$*
In a macro or string, the concatenation of all the arguments separated
by spaces.
.
.TP
.B \[rs]$@
In a macro or string, the concatenation of all the arguments with each
surrounded by double quotes, and separated by spaces.
.
.TP
.B \[rs]$^
In a macro, the representation of all parameters as if they were an
argument to the
.B ds
request.
.
.TP
.BI \[rs]$( nn
.TQ
.BI \[rs]$[ nnn ]
In a macro or string, this gives the
.IR nn -th
or
.IR nnn -th
argument.
.
Macros and strings can have an unlimited number of arguments.
.
.TP
.BI \[rs]? anything \[rs]?
When used in a diversion, this transparently embeds
.I anything
in the diversion.
.I anything
is read in copy mode.
.
When the diversion is reread,
.I anything
is interpreted.
.I anything
may not contain newlines; use
.B \[rs]!\&
if you want to embed newlines in a diversion.
.
The escape sequence
.B \[rs]?\&
is also recognized in copy mode and turned into a single internal
code; it is this code that terminates
.IR anything .
Thus
.
.RS
.IP
.EX
.ne 14v+\n(.Vu
\&.nr x 1
\&.nf
\&.di d
\&\[rs]?\[rs]\[rs]?\[rs]\[rs]\[rs]\[rs]?\[rs]\[rs]\[rs]\[rs]\[rs]\[rs]\[rs]\c
\&\[rs]nx\[rs]\[rs]\[rs]\[rs]?\[rs]\[rs]?\[rs]?
\&.di
\&.nr x 2
\&.di e
\&.d
\&.di
\&.nr x 3
\&.di f
\&.e
\&.di
\&.nr x 4
\&.f
.EE
.RE
.
.IP
prints\~\c
.BR 4 .
.
.TP
.B \[rs]/
This increases the width of the preceding glyph so that the
spacing between that glyph and the following glyph is
correct if the following glyph is a roman glyph.
.
.if t \{\
.  nop For example, if an italic\~f is immediately followed by a roman
.  nop right parenthesis, then in many fonts the top right portion of
.  nop the\~f overlaps the top left of the right parenthesis
.  nop producing \f[I]f\f[R]), which is ugly.
.  nop Inserting
.  B \[rs]/
.  nop produces
.  ie \n(.g \f[I]f\/\f[R])
.  el       \f[I]f\|\f[R])
.  nop and avoids this problem.
.\}
It is a good idea to use this escape sequence whenever an italic
glyph is immediately followed by a roman glyph without any
intervening space.
.
.TP
.B \[rs],
This modifies the spacing of the following glyph so that the
spacing between that glyph and the preceding glyph is
correct if the preceding glyph is a roman glyph.
.
.if t \{\
.  nop For example, inserting
.  B \[rs],
.  nop between the parenthesis and the\~f changes
.  nop \f[R](\f[I]f\f[R] to
.  ie \n(.g \f[R](\,\f[I]f\f[R].
.  el       \f[R](\^\f[I]f\f[R].
.\}
It is a good idea to use this escape sequence whenever a roman
glyph is immediately followed by an italic glyph without any
intervening space.
.
.TP
.B \[rs])
Like
.B \[rs]&
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 \[rs]\[ti]
This produces an unbreakable space that stretches like a normal
inter-word space when a line is adjusted.
.
.TP
.B \[rs]:
This causes the insertion of a zero-width break point.
.
It is equal to
.B \[rs]%
within a word but without insertion of a soft hyphen glyph.
.
.TP
.B \[rs]#
Everything up to and including the next newline is ignored.
.
This is interpreted in copy mode.
.
It is like
.B \[rs]"
except that
.B \[rs]"
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 are exactly equivalent.
.
If
.I yy
is undefined, a warning of type
.B reg
is generated, and the request is 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 are exactly equivalent (it is
similar to a hard rather than a soft link).
.
If
.I yy
is undefined, a warning of type
.B mac
is generated, and the request is 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 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.
.
To be more precise, a \[oq]compatibility save\[cq] token is inserted
at the beginning of the macro addition, and a \[oq]compatibility
restore\[cq] token at the end.
.
As a consequence, the requests
.BR am ,
.BR am1 ,
.BR de ,
and
.B de1
can be intermixed freely since the compatibility save/\:restore tokens
only affect the macro parts defined by
.B .am1
and
.BR .ds1 .
.
.TP
.BI .ami\  xx\ yy
Append to macro indirectly.
.
See the
.B dei
request below for more information.
.
.TP
.BI .ami1\  xx\ yy
Same as the
.B ami
request but compatibility mode is switched off during execution.
.
.TP
.BI .as1\  xx\ yy
Similar to
.BR .as ,
but compatibility mode is switched off during expansion.
.
To be more precise, a \[oq]compatibility save\[cq] token is inserted
at the beginning of the string, and a \[oq]compatibility restore\[cq]
token at the end.
.
As a consequence, the requests
.BR as ,
.BR as1 ,
.BR ds ,
and
.B ds1
can be intermixed freely since the compatibility save/\:restore tokens
only affect the (sub)strings defined by
.B as1
and
.BR ds1 .
.
.TP
.BI .asciify\  xx
This request \[oq]unformats\[cq] 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
are 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
.EX
.ne 7v+\n(.Vu
\&.tr @.
\&.di x
\&@nr n 1
\&.br
\&.di
\&.tr @@
\&.asciify x
\&.x
.EE
.RE
.
.IP
sets 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 is 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 does not
become part of the diversion (i.e., the diversion always starts with a
new line) but is 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 \[rs]p .
.
.TP
.BI .cflags\  "n c1 c2 \*[ellipsis]"
Characters
.IR c1 ,
.IR c2 ,
.IR \*[ellipsis] ,
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 is not broken at a character with this property
unless the characters on each side both have non-zero hyphenation
codes.
This can be overridden with value 64.
.
.IP 4
Lines can be broken after the character (initially characters
.B \-\[rs][hy]\[rs][em]
have this property); a line is not broken at a character with this
property unless the characters on each side both have non-zero
hyphenation codes.
This can be overridden with value 64.
.
.IP 8
The glyph associated with this character overlaps horizontally
(initially characters
.B \[rs][ul]\[rs][rn]\[rs][ru]\[rs][radicalex]\[rs][sqrtex]
have this property).
.
.IP 16
The glyph associated with this character overlaps vertically
(initially glyph
.B \[rs][br]
has this property).
.
.IP 32
An end-of-sentence character followed by any number of characters with
this property is treated as the end of a sentence if followed by a
newline or two spaces; in other words the character is transparent for
the purposes of end-of-sentence recognition; this is the same as having
a zero space factor in \*[tx] (initially characters
.B \[dq]')]*\[rs][dg]\[rs][rq]\[rs][cq]
have this property).
.
.IP 64
Ignore hyphenation code values of the surrounding characters.
Use this in combination with values 2 and\~4 (initially no characters
have this property).
.
.IP 128
Prohibit a line break before the character, but allow a line break after the
character.
This works only in combination with flags 256 and 512 and has no effect
otherwise.
.
.IP 256
Prohibit a line break after the character, but allow a line break before
the character.
This works only in combination with flags 128 and 512 and has no effect
otherwise.
.
.IP 512
Allow line break before or after the character.
This works only in combination with flags 128 and 256 and has no effect
otherwise.
.RE
.
.IP
Contrary to flag values 2 and\~4, the flags 128, 256, and 512 work
pairwise.
.
If, for example, the left character has value 512, and the right
character 128, no line break gets inserted.  If we use value\~6
instead for the left character, a line break after the character
can\[aq]t be suppressed since the right neighbour character
doesn\[aq]t get examined.
.
.TP
.BI .char\  c\ string
[This request can both define characters and glyphs.]
.
.IP
Define entity\~\c
.I c
to be
.IR string .
.
To be more precise, define (or even override) a groff entity which
can be accessed with name\~\c
.I c
on the input side, and which uses
.I string
on the output side.
.
Every time glyph\~\c
.I c
needs to be printed,
.I string
is processed in a temporary environment and the result is
wrapped up into a single object.
.
Compatibility mode is turned off and the escape character is
set to\~\c
.B \[rs]
while
.I string
is being processed.
.
Any emboldening, constant spacing or track kerning is applied to
this object rather than to individual glyphs in
.IR string .
.
.IP
A groff object defined by this request can be used just like a
normal glyph 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 glyph by the
.B lc
request; repeated patterns can be drawn with the glyph using the
.B \[rs]l
and
.B \[rs]L
escape sequences; words containing\~\c
.I c
can be hyphenated correctly, if the
.B hcode
request is used to give the object a hyphenation code.
.
.IP
There is a special anti-recursion feature: Use of glyph within the
glyph\[aq]s definition is handled like normal glyphs not defined with
.BR char .
.IP
A glyph definition can be removed with the
.B rchar
request.
.
.TP
.BI .chop\  xx
Chop the last element 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 .class\  "name c1 c2 \*[ellipsis]"
Assign
.I name
to a set of characters
.IR c1 ,
.IR c2 ,
.IR \*[ellipsis] ,
so that they can be referred to from other requests easily (currently
.B .cflags
only).
.
Character ranges (indicated by an intermediate \[oq]\-\[cq]) and
nested classes are possible also.
.
This is useful to assign properties to a large set of characters.
.
.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
.BI .composite\  glyph1\ glyph2
Map glyph name
.I glyph1
to glyph name
.I glyph2
if it is used in
.BI \[rs][ \*[ellipsis] ]
with more than one component.
.
.TP
.B .continue
Finish the current iteration of a while loop.
.
See also the
.B while
and
.B break
requests.
.
.TP
.BI .color\  n
If
.I n
is non-zero or missing, enable colors (this is the default), otherwise
disable them.
.
.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 recognized, and the
incompatibilities caused by long names do not arise.
.
.TP
.BI .defcolor\  xxx\ scheme\ color_components
Define color
.IR xxx .
.I scheme
can be one of the following values:
.B rgb
(three components),
.B cmy
(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\[en]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\[en]255 (which are
internally multiplied by\~257), the latter in the range 0\[en]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
.EX
\&.defcolor darkgreen rgb 0.1f 0.5f 0.2f
.EE
.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
.EX
\&.defcolor darkgreen rgb 0.1 0.5 0.2
.EE
.RE
.
.IP
The color named
.B default
(which is device-specific) can\[aq]t be redefined.
.
It is possible that the default color for
.B \[rs]M
and
.B \[rs]m
is not the same.
.
.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 .dei\  xx\ yy
Define macro indirectly.
.
The following example
.
.RS
.IP
.ne 2v+\n(.Vu
.EX
\&.ds xx aa
\&.ds yy bb
\&.dei xx yy
.EE
.RE
.
.IP
is equivalent to
.
.RS
.IP
.EX
\&.de aa bb
.EE
.RE
.
.TP
.BI .dei1\  xx\ yy
Similar to the
.B dei
request but compatibility mode is switched off during execution.
.
.TP
.BI .device\  anything
This is (almost) the same as the
.B \[rs]X
escape.
.I anything
is read in copy mode; a leading\~\c
.B \[dq]
is stripped.
.
.TP
.BI .devicem\  xx
This is the same as the
.B \[rs]Y
escape (to embed the contents of a macro into the intermediate
output preceded with \[oq]x\~X\[cq]).
.
.TP
.BI .do\  xxx
Interpret
.I .xxx
with compatibility mode disabled.
.
For example,
.
.RS
.
.IP
.EX
\&.do fam T
.EE
.
.P
would have the same effect as
.
.IP
.EX
\&.fam T
.EE
.
.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
.BI .ds1\  xx\ yy
Similar to
.BR .ds ,
but compatibility mode is switched off during expansion.
.
To be more precise, a \[oq]compatibility save\[cq] token is inserted
at the beginning of the string, and a \[oq]compatibility restore\[cq]
token at the end.
.
.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 \[oq] \[rs] \[cq]
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 is 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.
.
The value at start-up is \[oq]T\[cq].
.
See the description of the
.B sty
request for more information on font families.
.
.TP
.BI .fchar\  c\ string
Define fallback character (or glyph)\~\c
.I c
to be
.IR string .
.
The syntax of this request is the same as the
.B char
request; the only difference is that a glyph defined with
.B char
hides the glyph with the same name in the current font, whereas a
glyph defined with
.B fchar
is checked only if the particular glyph isn\[aq]t found in the current
font.
.
This test happens before checking special fonts.
.
.TP
.BI .fcolor\  c
Set the fill color to\~\c
.IR c .
If
.I c
is missing,
switch to the previous fill color.
.
.TP
.BI .fschar\  f\ c\ string
Define fallback character (or glyph)\~\c
.I c
for font\~\c
.I f
to be
.IR string .
.
The syntax of this request is the same as the
.B char
request (with an additional argument to specify the font); a glyph
defined with
.B fschar
is searched after the list of fonts declared with the
.B fspecial
request but before the list of fonts declared with
.BR .special .
.
.TP
.BI .fspecial\  "f s1 s2 \*[ellipsis]"
When the current font is\~\c
.IR f ,
fonts
.IR s1 ,
.IR s2 ,
.IR \*[ellipsis] ,
are special, that is, they are searched for glyphs not in
the current font.
.
Any fonts specified in the
.B special
request are searched after fonts specified in the
.B fspecial
request.
.
Without argument, reset the list of global special fonts to be empty.
.
.TP
.BI .ftr\  f\ g
Translate font\~\c
.I f
to\~\c
.IR g .
Whenever a font named\~\c
.I f
is referred to in an
.B \[rs]f
escape sequence, in the
.B F
and
.B S
conditional operators, or in the
.BR ft ,
.BR ul ,
.BR bd ,
.BR cs ,
.BR tkf ,
.BR special ,
.BR fspecial ,
.BR fp ,
or
.BR sty
requests, font\~\c
.I g
is used.
If
.I g
is missing, or equal to\~\c
.I f
then font\~\c
.I f
is not translated.
.
.TP
.BI .fzoom\  f\ zoom
Set zoom factor
.I zoom
for font\~\c
.IR f .
.I zoom
must a non-negative integer multiple of 1/1000th.
If it is missing or is equal to zero, it means the same as 1000, namely no
magnification.
.IR f \~\c
must be a real font name, not a style.
.
.TP
.BI .gcolor\  c
Set the glyph color to\~\c
.IR c .
If
.I c
is missing,
switch to the previous glyph color.
.
.TP
.BI .hcode\  "c1 code1 c2 code2 \*[ellipsis]"
Set the hyphenation code of character
.I c1
to
.I code1
and that of
.I c2
to
.IR code2 ,
and so on.
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 \%a\[en]z has a hyphenation code, which is
itself, and each upper-case letter \%A\[en]Z 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 to set up a default language.
.
.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 \[rs]%
are counted; explicit hyphens are not.
.
.TP
.BI .hpf\  file
Read hyphenation patterns from
.IR file ;
this is 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 (simple) \*[tx] patterns files.
.
More specifically, the following scanning rules are implemented.
.
.RS
.IP \[bu]
A percent sign starts a comment (up to the end of the line) even if
preceded by a backslash.
.
.IP \[bu]
No support for \[oq]digraphs\[cq] like
.BR \[rs]$ .
.
.IP \[bu]
.BI ^^ xx
.RI ( x
is 0\[en]9 or a\[en]f) and
.BI ^^ x
(character code of\~\c
.I x
in the range 0\[en]127) are recognized; other use of\~\c
.B ^
causes an error.
.
.IP \[bu]
No macro expansion.
.
.IP \[bu]
.B hpf
checks for the expression
.BR \[rs]patterns{ \*[ellipsis] }
(possibly with whitespace before and after the braces).
.
Everything between the braces is taken as hyphenation patterns.
.
Consequently,
.BR { \~\c
and\~\c
.B }
are not allowed in patterns.
.
.IP \[bu]
Similarly,
.BR \[rs]hyphenation{ \*[ellipsis] }
gives a list of hyphenation exceptions.
.
.IP \[bu]
.B \[rs]endinput
is recognized also.
.
.IP \[bu]
For backwards compatibility, if
.B \[rs]patterns
is missing, the whole file is treated as a list of hyphenation patterns
(only recognizing the
.BR % \~\c
character as the start of a comment).
.RE
.
.IP
Use the
.B hpfcode
request to map the encoding used in hyphenation patterns files to
.BR groff \[aq]s
input encoding.
.
By default, everything maps to itself except letters \[oq]A\[cq] to
\[oq]Z\[cq] which map to \[oq]a\[cq] to \[oq]z\[cq].
.
.IP
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; a second call replaces the old patterns with the new ones.
.
.TP
.BI .hpfa\  file
The same as
.B hpf
except that the hyphenation patterns from
.I file
are appended to the patterns already loaded in the current language.
.
.TP
.BI .hpfcode\  "a b c d \*[ellipsis]"
After reading a hyphenation patterns file with the
.B hpf
or
.B hpfa
request, convert all characters with character code\~\c
.I a
in the recently read patterns to character code\~\c
.IR b ,
character code\~\c
.I c
to\~\c
.IR d ,
etc.
.
Initially, all character codes map to themselves.
.
The arguments of
.B hpfcode
must be integers in the range 0 to\~255.
.
Note that it is even possible to use character codes which are invalid in
.B groff
otherwise.
.
.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 is not 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
.BR m .
The hyphenation margin is associated with the current environment.
.
The current hyphenation margin is available in the
.B \[rs]n[.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\[aq]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 \[rs]n[.hys]
register.
.
.TP
.BI .itc\  n\ macro
Variant of
.B .it
for which a line interrupted with
.B \[rs]c
counts as one input line.
.
.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
.EX
\&.ds x a\[rs]t\[rs]c
\&.ds y b\[rs]t\[rs]c
\&.ds z c
\&.ta 1i 3i
\&\[rs]*x
\&\[rs]*y
\&\[rs]*z
.EE
.RE
.
.IP
yields
.
.RS
.IP
.EX
a         b         c
.EE
.RE
.
.IP
In line-tabs mode, the same code gives
.
.RS
.IP
.EX
a         b                   c
.EE
.RE
.
.IP
Line-tabs mode is associated with the current environment; the
read-only number register
.B \[rs]n[.linetabs]
is set to\~1 if in line-tabs mode, and 0 otherwise.
.
.TP
.BI .lsm\  xx
Set the leading spaces macro to
.IR xx .
If there are leading spaces in an input line, it is invoked instead of
the usual troff behaviour; the leading spaces are removed.
Registers
.B \[rs]n[lsn]
and
.B \[rs]n[lss]
hold the number of removed leading spaces and the corresponding
horizontal space, respectively.
.
.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\[aq]t found,
.B mso
tries to include
.BI tmac. name
instead and vice versa.
.
A warning of type
.B file
is generated if
.I file
can\[aq]t be loaded, and the request is ignored.
.
.TP
.BI .nop \ anything
Execute
.IR anything .
This is similar to \[oq].if\ 1\[cq].
.
.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
.BI .output\  string
Emit
.I string
directly to the intermediate output (subject to copy-mode interpretation);
this is similar to
.B \[rs]!\&
used at the top level.
.
An initial double quote in
.I string
is stripped off to allow initial blanks.
.
.TP
.B .pev
Print the current environment and each defined environment state on
stderr.
.
.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\[aq]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 \[rs]n[llx] ,
.BR \[rs]n[lly] ,
.BR \[rs]n[urx] ,
and
.BR \[rs]n[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 .pvs \ \[+-]n
Set the post-vertical line space to\~\c
.IR n ;
default scale indicator is\~\c
.BR p .
.
This value is added to each line after it has been output.
.
With no argument, the post-vertical line space is set to its previous
value.
.
.IP
The total vertical line spacing consists of four components:
.B .vs
and
.B \[rs]x
with a negative value which are applied before the line is output, and
.B .pvs
and
.B \[rs]x
with a positive value which are applied after the line is output.
.
.TP
.BI .rchar\  "c1 c2 \*[ellipsis]"
Remove the definitions of glyphs
.IR c1 ,
.IR c2 ,
.I \*[ellipsis]
This undoes the effect of a
.B char
request.
.
.TP
.B .return
Within a macro, return immediately.
.
If called with an argument, return twice, namely from the current macro and
from the macro one level higher.
.
No effect otherwise.
.
.TP
.BI .rfschar\  "c1 c2 \*[ellipsis]"
Remove the font-specific definitions of glyphs
.IR c1 ,
.IR c2 ,
.I \*[ellipsis]
This undoes the effect of a
.B fschar
request.
.
.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 \[rs]n[.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 .schar\  c\ string
Define global fallback character (or glyph)\~\c
.I c
to be
.IR string .
.
The syntax of this request is the same as the
.B char
request; a glyph defined with
.B schar
is searched after the list of fonts declared with the
.B special
request but before the mounted special fonts.
.
.TP
.BI .shc\  c
Set the soft hyphen character to\~\c
.IR c .
If
.I c
is omitted, the soft hyphen character is set to the default
.BR \[rs][hy] .
The soft hyphen character is the glyph which is inserted when
a word is hyphenated at a line break.
.
If the soft hyphen character does not exist in the font of the
glyph immediately preceding a potential break point, then the line
is not 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
are no longer available.
.
If
.I n
is missing, arguments are shifted by\~1.
.
Shifting by negative amounts is currently undefined.
.
.TP
.BI .sizes\  s1\ s2\ \*[ellipsis]\ sn\  [0]
This command is similar to the
.B sizes
command of a
.B DESC
file.
.
It sets the available font sizes for the current font to
.IR s1 ,
.IR s2 ,
.IR \*[ellipsis]\| ,\~ sn
scaled points.
.
The list of sizes can be terminated by an optional\~\c
.BR 0 .
.
Each
.I si
can also be a range of sizes
.IR m \(en n .
.
Contrary to the font file command, the list can\[aq]t extend over more
than a single line.
.
.TP
.BI .special\  "s1 s2 \*[ellipsis]"
Fonts
.IR s1 ,
.IR s2 ,
.IR \*[ellipsis] ,
are special and are searched for glyphs not in the current
font.
.
Without arguments, reset the list of special fonts to be empty.
.
.TP
.BI .spreadwarn\  limit
Make
.B troff
emit a warning if the additional space inserted for each space between
words in an output line is larger or equal to
.IR limit .
.
A negative value is changed to zero; no argument toggles the warning on
and off without changing
.IR limit .
.
The default scaling indicator is\~\c
.BR m .
.
At startup,
.B spreadwarn
is deactivated, and
.I limit
is set to 3m.
.
For example,
.B .spreadwarn\ 0.2m
causes a warning if
.B troff
must add 0.2m or more for each interword space in a line.
.
This request is active only if text is justified to both margins (using
.BR .ad\ b ).
.
.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\~\c
.B R
and the current font family is\~\c
.BR T ,
then font
.BR TR
is 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 are applied instead to the
member of the current family corresponding to that style.
.
The default family can be set with the
.B \-f
command line option.
.
The
.B 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 named
.I xx
with the substring defined by the indices
.I n1
and
.IR n2 .
The first character in the string has index\~0.
.
If
.I n2
is omitted, it is taken to be equal to the string\[aq]s length.
.
If the index value
.I n1
or
.I n2
is negative, it is counted from the end of the string,
going backwards:
.
The last character has index\~\-1, the character before the last
character has index\~\-2, etc.
.
.TP
.BI .tkf\  f\ s1\ n1\ s2\ n2
Enable track kerning for font\~\c
.IR f .
When the current font is\~\c
.I f
the width of every glyph is 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 is increased by
.IR n1 ;
when it is greater than or equal to
.I s2
the width is 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
.B tm1
but without writing a final newline.
.
.TP
.BI .trf\  filename
Transparently output the contents of file
.IR filename .
Each line is output as if preceded by
.BR \[rs]! ;
however, the lines are not subject to copy-mode interpretation.
.
If the file does not end with a newline, then a newline is 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
.EX
\&.di x
\&.trf f
\&.di
.EE
.RE
.
.IP
Unlike with the
.B cf
request, the file cannot contain characters such as
.SM NUL
that are not valid troff input characters.
.
.TP
.BI .trin\  abcd
This is the same as the
.B tr
request except that the
.B asciify
request uses the character code (if any) before the character
translation.
.
Example:
.
.RS
.IP
.EX
\&.trin ax
\&.di xxx
\&a
\&.br
\&.di
\&.xxx
\&.trin aa
\&.asciify xxx
\&.xxx
.EE
.RE
.
.IP
The result is
.BR x\ a .
.
Using
.BR tr ,
the result would be
.BR x\ x .
.
.TP
.BI .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 \[rs]! .
For example,
.
.RS
.IP
.EX
\&.tr ab
\&.di x
\&\[rs]!.tm a
\&.di
\&.x
.EE
.RE
.
.IP
prints\~\c
.BR b ;
if
.B trnt
is used instead of
.B tr
it prints\~\c
.BR a .
.RE
.
.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 \[oq]unformats\[cq] 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
only handles 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.
.IR n \~\c
is the sum of the numbers associated with each warning that is to be
enabled; all other warnings are disabled.
.
The number associated with each warning is listed in
.BR troff (1).
.
For example,
.B .warn\~0
disables all warnings, and
.B .warn\~1
disables all warnings except that about missing glyphs.
.
If
.I n
is not given, all warnings are enabled.
.
.TP
.BI .warnscale\  si
Set the scaling indicator used in warnings to
.IR si .
.
Valid values for
.I si
are
.BR u ,
.BR i ,
.BR c ,
.BR p ,
and\~\c
.BR P .
.
At startup, it is set to\~\c
.BR i .
.
.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 \[rs]{
and the last line ends with
.BR \[rs]} .
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]
is stripped.
.
.TP
.BI .writec\  stream\ anything
Similar to
.B write
but without writing a final newline.
.
.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 escape sequences"
.\" --------------------------------------------------------------------
.
.TP
.BR \[rs]D' \*[ellipsis] '
All drawing commands of groff\[aq]s intermediate output are accepted.
.
See subsection
.B "Drawing Commands"
below for more information.
.
.
.\" --------------------------------------------------------------------
.SS "Extended requests"
.\" --------------------------------------------------------------------
.
.TP
.BI .cf\  filename
When used in a diversion, this embeds 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 .de\  xx\ yy
.TQ
.BI .am\  xx\ yy
.TQ
.BI .ds\  xx\ yy
.TQ
.BI .as\  xx\ yy
In compatibility mode, these requests behaves similar to
.BR .de1 ,
.BR .am1 ,
.BR .ds1 ,
and
.BR .as1 ,
respectively: A \[oq]compatibility save\[cq] token is inserted at the
beginning, and a \[oq]compatibility restore\[cq] token at the end,
with compatibility mode switched on during execution.
.
.TP
.BI .ev\  xx
If
.I xx
is not a number, this switches 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 are
created the first time that they are referenced.
.
.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
is 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 are added; if
two spaces follow the end of a sentence in the middle of a line, then
the second space is a sentence space.
.
Note that the behaviour of UNIX troff are 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 \*[ellipsis] nn " "T " "r1 r2 \*[ellipsis] rn"
Set tabs at positions
.IR n1 ,
.IR n2 ,
.IR \*[ellipsis] ,
.I nn
and then set tabs at
.IR nn \|+\| r1 ,
.IR nn \|+\| r2 ,
.IR \*[ellipsis] ,
.IR nn \|+\| rn
and then at
.IR nn \|+\| rn \|+\| r1 ,
.IR nn \|+\| rn \|+\| r2 ,
.IR \*[ellipsis] ,
.IR nn \|+\| rn \|+\| rn ,
and so on.
For example,
.
.RS
.IP
.EX
\&.ta T .5i
.EE
.
.P
sets tabs every half an inch.
.RE
.
.
.\" --------------------------------------------------------------------
.SS "New number registers"
.\" --------------------------------------------------------------------
.
The following read-only registers are available:
.
.TP
.B \[rs]n[.br]
Within a macro call, it is set to\~1 if the macro is called with the
\[oq]normal\[cq] control character (\[oq].\[cq] by default), and set
to\~0 otherwise.
.
This allows to reliably modify requests.
.
.RS
.IP
.ne 6v+\n(.Vu
.EX
\&.als bp*orig bp
\&.de bp
\&.tm before bp
\&.ie \[rs]\[rs]n[.br] .bp*orig
\&.el 'bp*orig
\&.tm after bp
\&..
.EE
.RE
.
.IP
Using this register outside of a macro makes no sense (it always returns
zero in such cases).
.
.TP
.B \[rs]n[.C]
1\~if compatibility mode is in effect, 0\~otherwise.
.
.TP
.B \[rs]n[.cdp]
The depth of the last glyph added to the current environment.
.
It is positive if the glyph extends below the baseline.
.
.TP
.B \[rs]n[.ce]
The number of lines remaining to be centered, as set by the
.B ce
request.
.
.TP
.B \[rs]n[.cht]
The height of the last glyph added to the current environment.
.
It is positive if the glyph extends above the baseline.
.
.TP
.B \[rs]n[.color]
1\~if colors are enabled, 0\~otherwise.
.
.TP
.B \[rs]n[.csk]
The skew of the last glyph added to the current environment.
.
The
.I skew
of a glyph is how far to the right of the center of a glyph
the center of an accent over that glyph should be placed.
.
.TP
.B \[rs]n[.ev]
The name or number of the current environment.
.
This is a string-valued register.
.
.TP
.B \[rs]n[.fam]
The current font family.
.
This is a string-valued register.
.
.TP
.B \[rs]n[.fn]
The current (internal) real font name.
.
This is a string-valued register.
.
If the current font is a style, the value of
.B \[rs]n[.fn]
is the proper concatenation of family and style name.
.
.TP
.B \[rs]n[.fp]
The number of the next free font position.
.
.TP
.B \[rs]n[.g]
Always\~1.
.
Macros should use this to determine whether they are running under GNU
troff.
.
.TP
.B \[rs]n[.height]
The current height of the font as set with
.BR \[rs]H .
.
.TP
.B \[rs]n[.hla]
The current hyphenation language as set by the
.B hla
request.
.
.TP
.B \[rs]n[.hlc]
The number of immediately preceding consecutive hyphenated lines.
.
.TP
.B \[rs]n[.hlm]
The maximum allowed number of consecutive hyphenated lines, as set by
the
.B hlm
request.
.
.TP
.B \[rs]n[.hy]
The current hyphenation flags (as set by the
.B hy
request).
.
.TP
.B \[rs]n[.hym]
The current hyphenation margin (as set by the
.B hym
request).
.
.TP
.B \[rs]n[.hys]
The current hyphenation space (as set by the
.B hys
request).
.
.TP
.B \[rs]n[.in]
The indentation that applies to the current output line.
.
.TP
.B \[rs]n[.int]
Set to a positive value if last output line is interrupted (i.e., if
it contains
.BR \[rs]c ).
.
.TP
.B \[rs]n[.kern]
1\~if pairwise kerning is enabled, 0\~otherwise.
.
.TP
.B \[rs]n[.lg]
The current ligature mode (as set by the
.B lg
request).
.
.TP
.B \[rs]n[.linetabs]
The current line-tabs mode (as set by the
.B linetabs
request).
.
.TP
.B \[rs]n[.ll]
The line length that applies to the current output line.
.
.TP
.B \[rs]n[.lt]
The title length as set by the
.B lt
request.
.
.TP
.B \[rs]n[.m]
The name of the current drawing color.
.
This is a string-valued register.
.
.TP
.B \[rs]n[.M]
The name of the current background color.
.
This is a string-valued register.
.
.TP
.B \[rs]n[.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 \[rs]n[.trunc]
register.
.
.TP
.B \[rs]n[.ns]
1\~if no-space mode is active, 0\~otherwise.
.
.TP
.B \[rs]n[.O]
The current output level as set with
.BR \[rs]O .
.
.TP
.B \[rs]n[.P]
1\~if the current page is in the output list set with
.BR \-o .
.
.TP
.B \[rs]n[.pe]
1\~during a page ejection caused by the
.B bp
request, 0\~otherwise.
.
.TP
.B \[rs]n[.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 \[rs]n[.ps]
The current point size in scaled points.
.
.TP
.B \[rs]n[.psr]
The last-requested point size in scaled points.
.
.TP
.B \[rs]n[.pvs]
The current post-vertical line space as set with the
.B pvs
request.
.
.TP
.B \[rs]n[.rj]
The number of lines to be right-justified as set by the
.B rj
request.
.
.TP
.B \[rs]n[.slant]
The slant of the current font as set with
.BR \[rs]S .
.
.TP
.B \[rs]n[.sr]
The last requested point size in points as a decimal fraction.
.
This is a string-valued register.
.
.TP
.B \[rs]n[.ss]
.TQ
.B \[rs]n[.sss]
These give the values of the parameters set by the first and second
arguments of the
.B ss
request.
.
.TP
.B \[rs]n[.sty]
The current font style.
.
This is a string-valued register.
.
.TP
.B \[rs]n[.tabs]
A string representation of the current tab settings suitable for use
as an argument to the
.B ta
request.
.
.TP
.B \[rs]n[.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 \[rs]n[.ne]
register.
.
.TP
.B \[rs]n[.U]
Set to\~1 if in safer mode and to\~0 if in unsafe mode (as given with
the
.B \-U
command line option).
.
.TP
.B \[rs]n[.vpt]
1\~if vertical position traps are enabled, 0\~otherwise.
.
.TP
.B \[rs]n[.warn]
The sum of the numbers associated with each of the currently enabled
warnings.
.
The number associated with each warning is listed in
.BR troff (1).
.
.TP
.B \[rs]n[.x]
The major version number.
.
For example, if the version number is 1.03, then
.B \[rs]n[.x]
contains\~1.
.
.TP
.B \[rs]n[.y]
The minor version number.
.
For example, if the version number is 1.03, then
.B \[rs]n[.y]
contains\~03.
.
.TP
.B \[rs]n[.Y]
The revision number of groff.
.
.TP
.B \[rs]n[.zoom]
The zoom value of the current font, in multiples of 1/1000th.
Zero if no magnification.
.
.TP
.B \[rs]n[llx]
.TQ
.B \[rs]n[lly]
.TQ
.B \[rs]n[urx]
.TQ
.B \[rs]n[ury]
These four read/\:write 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 \[rs]w
escape sequence:
.
.TP
.B \[rs]n[rst]
.TQ
.B \[rs]n[rsb]
Like the
.B st
and
.B sb
registers, but take account of the heights and depths of glyphs.
.
.TP
.B \[rs]n[ssc]
The amount of horizontal space (possibly negative) that should be
added to the last glyph before a subscript.
.
.TP
.B \[rs]n[skw]
How far to right of the center of the last glyph in the
.B \[rs]w
argument, the center of an accent from a roman font should be placed
over that glyph.
.
.P
Other available read/write number registers are:
.
.TP
.B \[rs]n[c.]
The current input line number.
.B \[rs]n[.c]
is a read-only alias to this register.
.
.TP
.B \[rs]n[hours]
The number of hours past midnight.
.
Initialized at start-up.
.
.TP
.B \[rs]n[hp]
The current horizontal position at input line.
.
.TP
.B \[rs]n[lsn]
.TQ
.B \[rs]n[lss]
If there are leading spaces in an input line, these registers
hold the number of leading spaces and the corresponding
horizontal space, respectively.
.
.TP
.B \[rs]n[minutes]
The number of minutes after the hour.
.
Initialized at start-up.
.
.TP
.B \[rs]n[seconds]
The number of seconds after the minute.
.
Initialized at start-up.
.
.TP
.B \[rs]n[systat]
The return value of the system() function executed by the last
.B sy
request.
.
.TP
.B \[rs]n[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 \[rs]n[year]
The current year.
.
Note that the traditional
.B troff
number register
.B \[rs]n[yr]
is the current year minus 1900.
.
.
.\" --------------------------------------------------------------------
.SS Miscellaneous
.\" --------------------------------------------------------------------
.
.B troff
predefines a single (read/write) string-based register,
.BR \[rs]*[.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 \[rs]n[.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 \[rs]n[.fp]
register; although
.B troff
does not enforce this strictly, it does 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\  \[rs]\[rs]$@
.P
is
.
.IP
.BI \[rs]\[rs]*[ xx ]\[rs]\[rs]
.
.P
If the font description file contains pairwise kerning information,
glyphs from that font are kerned.
.
Kerning between two glyphs can be inhibited by placing a
.B \[rs]&
between them.
.
.P
In a string comparison in a condition, characters that appear at
different input levels to the first delimiter character are not
recognized as the second or third delimiters.
.
This applies also to the
.B tl
request.
.
In a
.B \[rs]w
escape sequence, a character that appears at a different input level
to the starting delimiter character is not recognized as the
closing delimiter character.
.
The same is true for
.BR \[rs]A ,
.BR \[rs]b ,
.BR \[rs]B ,
.BR \[rs]C ,
.BR \[rs]l ,
.BR \[rs]L ,
.BR \[rs]o ,
.BR \[rs]X ,
and
.BR \[rs]Z .
.
When decoding a macro or string argument that is delimited by double
quotes, a character that appears at a different input level to the starting
delimiter character is not recognized as the closing delimiter
character.
.
The implementation of
.B \[rs]$@
ensures that the double quotes surrounding an argument appear at the
same input level, which is different to the input level of the
argument itself.
.
In a long escape name
.B ]
is not recognized as a closing delimiter except when it occurs at
the same input level as the opening\~\c
.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 (or glyph)
.IR ch
available;
.I ch
is either an
.SM ASCII
character or a glyph (special character)
.BI \[rs]N' xxx '\f[R],
.BI \[rs]( xx
or
.BI \[rs][ xxx ]\f[R];
the condition is also true if
.I ch
has been defined by the
.B char
request.
.
.TP
.BI .if\ F f
True if font\~\c
.I f
exists.
.
.BR f \~\c
is handled as if it was opened with the
.B ft
request (this is, font translation and styles are applied), without
actually mounting it.
.
.TP
.BI .if\ S s
True if style\~\c
.I s
has been registered.
.
Font translation is applied.
.
.P
The
.B tr
request can now map characters onto
.BR \[rs]\[ti] .
.
.P
The space width emitted by the
.B \[rs]|
and
.B \[rs]^
escape sequences can be controlled on a per-font basis.
If there is a glyph named
.B \[rs]|
or
.BR \[rs]^ ,
respectively (note the leading backslash), defined in the current font file,
use this glyph\[aq]s width instead of the default value.
.
.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
.EX
\&.if t \[rs]{\[rs]
\&.  de bar
\&.    nop Hello, I\[aq]m \[oq]bar\[cq].
\&.  .
\&.\[rs]}
.EE
.
.
.\" --------------------------------------------------------------------
.SH "INTERMEDIATE OUTPUT FORMAT"
.\" --------------------------------------------------------------------
.
This section describes the format output by GNU troff.
.
The output format used by GNU troff is very similar to that used
by Unix device-independent troff.
.
Only the differences are documented here.
.
.
.\" --------------------------------------------------------------------
.SS "Units"
.\" --------------------------------------------------------------------
.
The argument to the
.BR s \~\c
command is in scaled points (units of
.RI points/ n ,
where
.I n
is the argument to the
.B sizescale
command  in the DESC file).
.
The argument to the
.B x\ Height
command is also in scaled points.
.
.
.\" --------------------------------------------------------------------
.SS "Text Commands"
.\" --------------------------------------------------------------------
.
.TP
.BI N n
Print glyph with index\~\c
.I n
(a non-negative integer) of the current font.
.
.P
If the
.B tcommand
line is present in the DESC file, troff uses the following two
commands.
.
.TP
.BI t xxx
.I xxx
is any sequence of characters terminated by a space or a newline (to
be more precise, it is a sequence of glyphs which are accessed with
the corresponding characters); the first character should be printed at
the current position, the current horizontal position should be increased
by the width of the first character, and so on for each character.
.
The width of the glyph is that given in the font file,
appropriately scaled for the current point size, and rounded so that
it is a multiple of the horizontal resolution.
.
Special characters cannot be printed using this command.
.
.TP
.BI u n\ xxx
This is same as the
.BR t \~\c
command except that after printing each character, the current
horizontal position is increased by the sum of the width of that
character and\~\c
.IR n .
.
.P
Note that single characters can have the eighth bit set, as can the
names of fonts and special characters.
.
.P
The names of glyphs and fonts can be of arbitrary length; drivers
should not assume that they are only two characters long.
.
.P
When a glyph is to be printed, that glyph is always
in the current font.
.
Unlike device-independent troff, it is not necessary for drivers to
search special fonts to find a glyph.
.
.P
For color support, some new commands have been added:
.
.TP
\f[B]mc \f[I]cyan magenta yellow\f[R]
.TQ
\f[B]md\f[R]
.TQ
\f[B]mg \f[I]gray\f[R]
.TQ
\f[B]mk \f[I]cyan magenta yellow black\f[R]
.TQ
\f[B]mr \f[I]red green blue\f[R]
Set the color components of the current drawing color, using various
color schemes.
.
.B md
resets the drawing color to the default value.
.
The arguments are integers in the range 0 to 65536.
.
.P
The
.BR x \~\c
device control command has been extended.
.
.TP
\f[B]x u \f[I]n\f[R]
If
.I n
is\~1, start underlining of spaces.
.
If
.I n
is\~0, stop underlining of spaces.
.
This is needed for the
.B cu
request in nroff mode and is ignored otherwise.
.
.
.\" --------------------------------------------------------------------
.SS "Drawing Commands"
.\" --------------------------------------------------------------------
.
The
.B D
drawing command has been extended.
.
These extensions are not used by GNU pic if the
.B \-n
option is given.
.
.TP
\f[B]Df \f[I]n\/\f[R]\*[ic]\[rs]n
Set the shade of gray to be used for filling solid objects to
.IR n ;
.I n
must be an integer between 0 and 1000, where 0 corresponds solid white
and 1000 to solid black, and values in between correspond to
intermediate shades of gray.
.
This applies only to solid circles, solid ellipses and solid
polygons.
.
By default, a level of 1000 is used.
.
Whatever color a solid object has, it should completely obscure
everything beneath it.
.
A value greater than 1000 or less than\~0 can also be used: this means
fill with the shade of gray that is currently being used for lines and
text.
.
Normally this is black, but some drivers may provide a way of
changing this.
.
.IP
The corresponding
.BI \[rs]D'f \*[ellipsis] '
command shouldn\[aq]t be used since its argument is always rounded to an
integer multiple of the horizontal resolution which can lead to
surprising results.
.
.TP
\f[B]DC \f[I]\/d\f[R]\*[ic]\[rs]n
Draw a solid circle with a diameter of
.I d
with the leftmost point at the current position.
.
.TP
\f[B]DE \f[I]dx dy\/\f[R]\*[ic]\[rs]n
Draw a solid ellipse with a horizontal diameter of
.I dx
and a vertical diameter of
.I dy
with the leftmost point at the current position.
.EQ
delim $$
.EN
.
.TP
\f[B]Dp\f[R] $dx sub 1$ $dy sub 1$ $dx sub 2$ $dy sub 2$ $...$ $dx sub n$ $dy sub n$\[rs]n
Draw a polygon with, for $i = 1 ,..., n+1$, the
.IR i -th
vertex at the current position
.
$+ sum from j=1 to i-1 ( dx sub j , dy sub j )$.
.
At the moment, GNU pic only uses this command to generate triangles
and rectangles.
.
.TP
\f[B]DP\f[R] $dx sub 1$ $dy sub 1$ $dx sub 2$ $dy sub 2$ $...$ $dx sub n$ $dy sub n$\[rs]n
.
Like
.B Dp
but draw a solid rather than outlined polygon.
.
.TP
\f[B]Dt \f[I]n\/\f[R]\*[ic]\[rs]n
Set the current line thickness to
.IR n \~\c
machine units.
.
Traditionally Unix troff drivers use a line thickness proportional to
the current point size; drivers should continue to do this if no
.B Dt
command has been given, or if a
.B Dt
command has been given with a negative value of\~\c
.IR n .
A zero value of\~\c
.I n
selects the smallest available line thickness.
.
.P
A difficulty arises in how the current position should be changed after
the execution of these commands.
.
This is not of great importance since the code generated by GNU pic
does not depend on this.
.
Given a drawing command of the form
.IP
\f[B]\[rs]D'\f[I]c\f[R] $x sub 1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x sub n$ $y sub n$\f[B]'\f[R]
.
.P
where
.I c
is not one of
.BR c ,
.BR e ,
.BR l ,
.BR a ,
or\~\c
.BR \[ti] ,
Unix troff treats each of the $x sub i$ as a horizontal quantity,
and each of the $y sub i$ as a vertical quantity and assumes that
the width of the drawn object is $sum from i=1 to n x sub i$,
and that the height is $sum from i=1 to n y sub i$.
.
(The assumption about the height can be seen by examining the
.B st
and
.B sb
registers after using such a
.BR D \~\c
command in a
.B \[rs]w
escape sequence).
.
This rule also holds for all the original drawing commands with the
exception of
.BR De .
For the sake of compatibility GNU troff also follows this rule, even
though it produces an ugly result in the case of the
.B Dt
and
.BR Df ,
and, to a lesser extent,
.B DE
commands.
.
Thus after executing a
.BR D \~\c
command of the form
.IP
\f[B]D\f[I]c\f[R] $x sub 1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x sub n$ $y sub n$\[rs]n
.
.P
the current position should be increased by
.
$( sum from i=1 to n x sub i , sum from i=1 to n y sub i )$.
.
.P
Another set of extensions is
.
.TP
\f[B]DFc \f[I]cyan magenta yellow\f[R]\*[ic]\[rs]n
.TQ
\f[B]DFd\f[R]\*[ic]\[rs]n
.TQ
\f[B]DFg \f[I]gray\/\f[R]\*[ic]\[rs]n
.TQ
\f[B]DFk \f[I]cyan magenta yellow black\f[R]\*[ic]\[rs]n
.TQ
\f[B]DFr \f[I]red green blue\f[R]\*[ic]\[rs]n
Set the color components of the filling color similar to the
.BR m \~\c
commands above.
.
.P
The current position isn\[aq]t changed by those colour commands
(contrary to
.BR Df ).
.
.
.\" --------------------------------------------------------------------
.SS "Device Control Commands"
.\" --------------------------------------------------------------------
.
There is a continuation convention which permits the argument to the
.B x\ X
command to contain newlines: when outputting the argument to the
.B x\ X
command, GNU troff follows each newline in the argument with a
.B +
character (as usual, it terminates the entire argument with a
newline); thus if the line after the line containing the
.B x\ X
command starts with
.BR + ,
then the newline ending the line containing the
.B x\ X
command should be treated as part of the argument to the
.B x\ X
command, the
.B +
should be ignored, and the part of the line following the
.B +
should be treated like the part of the line following the
.B x\ X
command.
.
.P
The first three output commands are guaranteed to be:
.IP
.BI x\ T\  device
.br
.BI x\ res\  n\ h\ v
.br
.B x init
.
.
.\" --------------------------------------------------------------------
.SH INCOMPATIBILITIES
.\" --------------------------------------------------------------------
.
In spite of the many extensions, groff has retained compatibility to
classical troff to a large degree.
.
For the cases where the extensions lead to collisions, a special
compatibility mode with the restricted, old functionality was created
for groff.
.
.
.\" --------------------------------------------------------------------
.SS "Groff Language"
.\" --------------------------------------------------------------------
.
.I groff
provides a
.B compatibility mode
that allows to process roff code written for classical
.B troff
or for other implementations of roff in a consistent way.
.
.P
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 \[rs]n(.C
is\~1 if compatibility mode is on, 0\~otherwise.
.
.P
This became necessary because the GNU concept for long names causes
some incompatibilities.
.I Classical troff
interprets
.IP
.B .dsabcd
.
.P
as defining a string
.B ab
with contents
.BR cd .
In
.IR groff
mode, this is considered as a call of a macro named
.BR dsabcd .
.
.P
Also
.I classical troff
interprets
.B \[rs]*[
or
.B \[rs]n[
as references to a string or number register called\~\c
.B [
while
.I groff
takes this as the start of a long name.
.
.P
In
.IR "compatibility mode" ,
groff interprets these things in the traditional way; so long
names are not recognized.
.
.P
On the other hand, groff in
.I GNU native mode
does not allow to use the single-character escapes
.B \[rs]\[rs]
(backslash),
.B \[rs]|
(vertical bar),
.B \[rs]^
(caret),
.B \[rs]&
(ampersand),
.B \[rs]{
(opening brace),
.B \[rs]}
(closing brace),
.RB \[oq] \[rs]\  \[cq]
(space),
.B \[rs]'
(single quote),
.B \[rs]`
(backquote),
.B \[rs]\-
(minus),
.B \[rs]_
(underline),
.B \[rs]!\&
(bang),
.B \[rs]%
(percent),
and
.B \[rs]c
(character\~c) in names of strings, macros, diversions, number
registers, fonts or environments, whereas
.I classical troff
does.
.
.P
The
.B \[rs]A
escape sequence can be helpful in avoiding these escape sequences in
names.
.
.P
Fractional point sizes cause one noteworthy incompatibility.
.
In
.I classical
.IR troff ,
the
.B ps
request ignores scale indicators and so
.RS
.P
.B .ps\~10u
.RE
.
.P
sets the point size to 10\~points, whereas in groff native mode the
point size is set to 10\~scaled points.
.
.P
In
.IR groff ,
there is a fundamental difference between unformatted input
characters, and formatted output characters (glyphs).
.
Everything that affects how a glyph is output is
stored with the glyph; once a glyph has been
constructed it is unaffected by any subsequent requests that are
executed, including the
.BR bd ,
.BR cs ,
.BR tkf ,
.BR tr ,
or
.B fp
requests.
.
.P
Normally glyphs are constructed from input characters at
the moment immediately before the glyph is added to the current
output line.
.
Macros, diversions and strings are all, in fact, the same type of
object; they contain lists of input characters and glyphs
in any combination.
.
.P
Special characters can be both; before being added to the output, they
act as input entities, afterwards they denote glyphs.
.
.P
A glyph 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.
.
The following example makes things clearer.
.
.P
.RS
.EX
\&.di x
\[rs]\[rs]\[rs]\[rs]
\&.br
\&.di
\&.x
.EE
.RE
.
.P
With
.I GNU troff
this is printed as
.BR \[rs]\[rs] .
So each pair of input backslashes \&\[oq]\[rs]\[rs]\[cq] is turned
into a single output backslash glyph \&\[oq]\[rs]\[cq] and the
resulting output backslashes are not interpreted as escape characters
when they are reread.
.
.P
.I Classical troff
would interpret them as escape characters when they were reread and
would end up printing a single backslash \[oq]\[rs]\[cq].
.
.P
In GNU, the correct way to get a printable version of the backslash
character \[cq]\[rs]\[cq]
is the
.B \[rs](rs
escape sequence, but classical troff does not provide a clean feature
for getting a non-syntactical backslash.
.
A close method is the printable version of the current escape
character using the
.B \[rs]e
escape sequence; this works if the current escape character is not
redefined.
.
It works in both GNU mode and compatibility mode, while dirty tricks
like specifying a sequence of multiple backslashes do not work
reliably; for the different handling in diversions, macro definitions,
or text mode quickly leads to a confusion about the necessary number of
backslashes.
.
.P
To store an escape sequence in a diversion that is interpreted
when the diversion is reread, either the traditional
.B \[rs]!\&
transparent output facility or the
new
.B \[rs]?\&
escape sequence can be used.
.
.
.\" --------------------------------------------------------------------
.SS "Intermediate Output"
.\" --------------------------------------------------------------------
.
The groff intermediate output format is in a state of evolution.
.
So far it has some incompatibilities, but it is intended to establish
a full compatibility to the classical troff output format.
.
Actually the following incompatibilities exist:
.
.IP \[bu] 2m
The positioning after the drawing of the polygons conflicts with the
classical definition.
.
.IP \[bu] 2m
The intermediate output cannot be rescaled to other devices as
classical \[oq]device-independent\[cq] troff did.
.
.
.\" --------------------------------------------------------------------
.SH "SEE ALSO"
.\" --------------------------------------------------------------------
.
The
.I groff info
.IR file ,
cf.\&
.BR info (1)
presents all groff documentation within a single document.
.
.TP
.BR groff (1)
A list of all documentation around
.IR groff .
.
.TP
.BR groff (7)
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 using
.
.RS
.IP
.EX
man 7 groff
.EE
.RE
.
.TP
.BR roff (7)
A survey of
.I roff
systems, including pointers to further historical documentation.
.
.TP
.RI [ CSTR\~#54\/ ]
The
.I Nroff/\:Troff User\[aq]s Manual
by
.I J.\& F.\& Ossanna
of 1976 in the revision of
.I Brian Kernighan
of 1992, being the
.UR http://\:cm.bell-labs.com/\:cm/\:cs/\:cstr/\:54.ps.gz
classical troff documentation
.UE .
.
.
.\" --------------------------------------------------------------------
.SH COPYING
.\" --------------------------------------------------------------------
.co
.\" --------------------------------------------------------------------
.SH AUTHORS
.\" --------------------------------------------------------------------
.au
.
.
.\" --------------------------------------------------------------------
.\" Emacs variables
.\" --------------------------------------------------------------------
.
.\" Local Variables:
.\" mode: nroff
.\" End: