freebsd/contrib/groff/man/groff_out.man

'\" e
.\" The above line should force the use of eqn as a preprocessor
.ig
groff_out.5

Last update: 13 Apr 2003

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

Copyright (C) 1989, 2001, 2002, 2003 Free Software Foundation, Inc.
rewritten from scrach 2001 by 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 AUTHORS, 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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.\" Number register to decide whether the commands `{' and `}' are used
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Unfortunately, old versions of groff used an illogical position change
after some D\~commands (Dp, DP, Dt).  If the number register
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.\" ----------------- Syntactical definitions
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.\" comments when escapes are switched off
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.c format: .unit <letter> <punctuation>
.de unit
.  BR \$@
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.c argument in italic with punctuation
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.  if (\n[.$] == 0) \
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.  IR \$@
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.c comma separated list of indexed variables
.de list1..n
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.  if (\n[.$] < 2) \
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.  if (\n[.$] < 4) \
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.  shift 4
.  ie t \{\
.    ie \B'\*[@index1]' \{\
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.    el \{\
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.      nop $\*[@arg2] sub \*[@index2]$)\$* \c
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.  el \{\
.    nop (\f[I]\*[@arg1]\*[@index1]\f[],\ \c
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.de D-command
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.\" End of macro definitions 
.
.
.\" --------------------------------------------------------------------
.\" Title
.\" --------------------------------------------------------------------
.
.TH GROFF_OUT @MAN5EXT@ "@MDATE@" "Groff Version @VERSION@"
.
.SH NAME
groff_out \- groff intermediate output format
.
.
.\" --------------------------------------------------------------------
.SH DESCRIPTION
.\" --------------------------------------------------------------------
.
This manual page describes the intermediate output format of the GNU
.BR roff (@MAN7EXT@)
text processing system.
.
This output is produced by a run of the GNU
.BR troff (@MAN1EXT@)
program before it is fed into a device postprocessor program.
.
.P
As the GNU roff processor
.BR groff (@MAN1EXT@)
is a wrapper program around troff that automatically calls a
postprocessor, this output does not show up normally.
.
This is why it is called
.I intermediate
within the
.I groff
.IR system .
.
The
.B groff
program provides the option
.B -Z
to inhibit postprocessing, such that the produced intermediate output
is sent to standard output just like calling
.B troff
manually.
.
.P
In this document, the term
.I troff output
describes what is output by the GNU troff program, while
.I intermediate output
refers to the language that is accepted by the parser that prepares
this output for the postprocessors.
.
This parser is smarter on whitespace and implements obsolete elements
for compatibility, otherwise both formats are the same.
.
The pre-groff roff versions are denoted as
.I classical
.IR troff .
.
.P
The main purpose of the intermediate output concept is to facilitate
the development of postprocessors by providing a common programming
interface for all devices.
.
It has a language of its own that is completely different from the
.BR groff (@MAN7EXT@)
language.
.
While the
.I groff
language is a high-level programming language for text processing, the
intermediate output language is a kind of low-level assembler language
by specifying all positions on the page for writing and drawing.
.
.P
The intermediate output produced by
.I groff
is fairly readable, while
.I classical troff
output was hard to understand because of strange habits that are
still supported, but not used any longer by
.I GNU
.IR troff .
.
.
.\" --------------------------------------------------------------------
.SH "LANGUAGE CONCEPTS"
.\" --------------------------------------------------------------------
.
During the run of
.BR troff , 
the roff input is cracked down to the information on what has to be
printed at what position on the intended device.
.
So the language of the intermediate output format can be quite small.
.
Its only elements are commands with or without arguments.
.
In this document, the term "command" always refers to the intermediate
output language, never to the roff language used for document
formatting.
.
There are commands for positioning and text writing, for drawing, and
for device controlling.
.
.
.\" --------------------------------------------------------------------
.SS "Separation"
.\" --------------------------------------------------------------------
.
.I Classical troff output
had strange requirements on whitespace.
.
The
.I groff
output parser, however, is smart about whitespace by making it
maximally optional.
.
The whitespace characters, i.e.\& the
.IR tab ,
.IR space ,
and
.I newline
characters, always have a syntactical meaning.
.
They are never printable because spacing within the output is always
done by positioning commands.
.
.P
Any sequence of
.I space
or
.I tab
characters is treated as a single
.B syntactical
.BR space .
.
It separates commands and arguments, but is only required when there
would occur a clashing between the command code and the arguments
without the space.
.
Most often, this happens when variable length command names,
arguments, argument lists, or command clusters meet.
.
Commands and arguments with a known, fixed length need not be
separated by syntactical space.
.
.P
A line break is a syntactical element, too.
.
Every command argument can be followed by whitespace, a comment, or a
newline character.
.
Thus a
.B syntactical line break
is defined to consist of optional syntactical space that is optionally
followed by a comment, and a newline character.
.
.P
The normal commands, those for positioning and text, consist of a
single letter taking a fixed number of arguments.
.
For historical reasons, the parser allows to stack such commands on
the same line, but fortunately, in groff intermediate output, every
command with at least one argument is followed by a line break, thus
providing excellent readability.
.
.P
The other commands \[em] those for drawing and device controlling \[em]
have a more complicated structure; some recognize long command names,
and some take a variable number of arguments.
.
So all
.B D
and
.B x
commands were designed to request a
.I syntactical line break
after their last argument.
.
Only one command,
.RB ` x\ X '
has an argument that can stretch over several lines, all other
commands must have all of their arguments on the same line as the
command, i.e.\& the arguments may not be splitted by a line break.
.
.P
Empty lines, i.e.\& lines containing only space and/or a comment, can
occur everywhere.
.
They are just ignored.
.
.
.\" --------------------------------------------------------------------
.SS "Argument Units"
.\" --------------------------------------------------------------------
.
Some commands take integer arguments that are assumed to represent
values in a measurement unit, but the letter for the corresponding
.I scale indicator
is not written with the output command arguments; see
.BR groff (@MAN7EXT@)
and the groff info file for more on this topic.
.
Most commands assume the scale indicator\~\c
.unit u ,
the basic unit of the device, some use\~\c
.unit z , 
the
.I scaled point unit
of the device, while others, such as the color commands expect plain
integers.
.
Note that these scale indicators are relative to the chosen device.
.
They are defined by the parameters specified in the device's
.I DESC
file; see
.BR groff_font (@MAN5EXT@).
.
.P
Note that single characters can have the eighth bit set, as can the
names of fonts and special characters.
.
The names of characters and fonts can be of arbitrary length.
.
A character that is to be printed will always be in the current font.
.
.P
A string argument is always terminated by the next whitespace
character (space, tab, or newline); an embedded
.B #
character is regarded as part of the argument, not as the beginning of
a comment command.
.
An integer argument is already terminated by the next non-digit
character, which then is regarded as the first character of the next
argument or command.
.
.
.\" --------------------------------------------------------------------
.SS "Document Parts"
.\" --------------------------------------------------------------------
A correct intermediate output document consists of two parts, the
prologue and the body.
.
.P
The task of the
.I prologue
is to set the general device parameters using three exactly specified
commands.
.
The
.I groff prologue
is guaranteed to consist of the following three lines (in that order):
.RS
.P
.B x\ T
.I device
.br
.B x\ res
.I n\ h\ v
.br
.B x init
.RE
.P
with the arguments set as outlined in the section
.BR "Device Control Commands" .
.
But the parser for the intermediate output format is able to swallow
additional whitespace and comments as well.
.
.P
The
.I body
is the main section for processing the document data.
.
Syntactically, it is a sequence of any commands different from the
ones used in the prologue.
.
Processing is terminated as soon as the first
.B x\ stop
command is encountered; the last line of any groff intermediate output
always contains such a command.
.
.P
Semantically, the body is page oriented.
.
A new page is started by a
.BR p \~command.
.
Positioning, writing, and drawing commands are always done within the
current page, so they cannot occur before the first
.BR p \~command.
.
Absolute positioning (by the
.B H
and
.BR V \~commands)
is done relative to the current page, all other positioning
is done relative to the current location within this page.
.
.
.\" --------------------------------------------------------------------
.SH "COMMAND REFERENCE"
.\" --------------------------------------------------------------------
.
This section describes all intermediate output commands, the classical
commands as well as the
.I groff
extensions.
.
.
.\" --------------------------------------------------------------------
.SS "Comment Command"
.\" --------------------------------------------------------------------
.
.TP
.BI # anything \[la]end_of_line\[ra]
A comment.
.
Ignore any characters from the
.BR # \~\c
character up to the next newline character.
.
.P
This command is the only possibility for commenting in the intermediate
output.
.
Each comment can be preceded by arbitrary
.I syntactical
.IR space ;
every command can be terminated by a comment.
.
.
.\" --------------------------------------------------------------------
.SS "Simple Commands"
.\" --------------------------------------------------------------------
.
The commands in this subsection have a command code consisting of a
single character, taking a fixed number of arguments.
.
Most of them are commands for positioning and text writing.
.
These commands are smart about whitespace.
.
Optionally,
.I syntactical space
can be inserted before, after, and between the command letter and its
arguments.
.
All of these commands are stackable, i.e., they can be preceded by
other simple commands or followed by arbitrary other commands on the
same line.
.
A separating syntactical space is only necessary when two integer
arguments would clash or if the preceding argument ends with a string
argument.
.
.
.if (\n[@USE_ENV_STACK] == 1) \{\
.command {
Open a new environment by copying the actual device configuration data
to the environment stack.
.
The current environment is setup by the device specification and
manipulated by the setting commands.
.
.
.command }
Close the actual environment (opened by a preceding
.BR { \~command)
and restore the previous environment from the environment
stack as the actual device configuration data.
.
\}              \" endif @USE_ENV_STACK
.
.
.command C xxx \[la]white_space\[ra]
Print a special groff character named
.argument xxx .
.
The trailing syntactical space or line break is necessary to allow
character names of arbitrary length.
.
The character is printed at the current print position;
the character's size is read from the font file.
.
The print position is not changed.
.
.
.command c c
Print character\~\c
.argument c
at the current print position;
the character's size is read from the font file.
.
The print position is not changed.
.
.
.command f n
Set font to font number\~\c
.argument n
(a non-negative integer).
.
.
.command H n
Move right to the absolute vertical position\~\c
.argument n
(a non-negative integer in basic units\~\c
.unit u )
relative to left edge of current page.
.
.
.command h n
Move
.argument n
(a non-negative integer) basic units\~\c
.unit u
horizontally to the right.
.
.I [54]
allows negative values for
.I n
also, but
.I groff
doesn't use this.
.
.
.command m "color_scheme \f[R][\f[]component .\|.\|.\f[R]]\f[]"
Set the color for text (glyphs), line drawing, and the outline of
graphic objects using different color schemes; the analoguous command
for the filling color of graphic objects is
.BR DF .
.
The color components are specified as integer arguments between 0 and
\n[@maxcolor].
.
The number of color components and their meaning vary for the
different color schemes.
.
These commands are generated by the groff escape sequence
.BR \*[@backslash]m .
.
No position changing.
.
These commands are a groff extension.
.
.
.RS
.
.command mc "cyan magenta yellow"
Set color using the CMY color scheme, having the 3\~color components
cyan, magenta, and yellow.
.
.
.command md
Set color to the default color value
(black in most cases).
.
No component arguments.
.
.
.command mg "gray"
Set color to the shade of gray given by the argument, an integer
between 0 (black) and \n[@maxcolor] (white).
.
.
.command mk "cyan magenta yellow black"
Set color using the CMYK color scheme, having the 4\~color components
cyan, magenta, yellow, and black.
.
.command mr "red green blue"
Set color using the RGB color scheme, having the 3\~color components
red, green, and blue.
.
.RE
.
.
.command N n
Print character with index\~\c
.argument n
(an integer, normally non-negative) of the current font.
.
The print position is not changed.
.
If
.B \-T\~html
is used, negative values are emitted also to indicate an unbreakable space
with given width.
.
For example,
.B N\~-193
represents an unbreakable space which has a width of 193u.
.
This command is a groff extension.
.
.
.command n b\ a
Inform the device about a line break, but no positioning is done by
this command.
.
In classical troff, the integer arguments
.argument b
and\~\c
.argument a
informed about the space before and after the current line to
make the intermediate output more human readable without performing
any action.
.
In groff, they are just ignored, but they must be provided for
compatibility reasons.
.
.
.command p n
Begin a new page in the outprint.
.
The page number is set to\~\c
.argument n .
.
This page is completely independent of pages formerly processed even
if those have the same page number.
.
The vertical position on the outprint is automatically set to\~0.
.
All positioning, writing, and drawing is always done relative to a
page, so a
.BR p \~command
must be issued before any of these commands.
.
.
.command s n
Set point size to
.argument n
scaled points
(this is unit\~\c
.unit z
in GNU
.BR troff ).
.
Classical troff used the unit
.I points
(\c
.unit p )
instead; see section
.BR COMPATIBILITY .
.
.
.command t xxx \[la]white_space\[ra]
.command+ t "xxx dummy_arg" \[la]white_space\[ra]
Print a word, i.e.\& a sequence of characters
.argument xxx
terminated by a space character or a line break; an optional second
integer argument is ignored (this allows the formatter to generate
an even number of arguments).
.
The first character should be printed at the current position, the
current horizontal position should then be increased by the width of
the first character, and so on for each character.
.
The widths of the characters are read from the font file, scaled for the
current point size, and rounded to a multiple of the horizontal
resolution.
.
Special characters cannot be printed using this command (use the
.B C
command for named characters).
.
This command is a groff extension; it is only used for devices whose
.I DESC
file contains the
.B tcommand
keyword; see
.BR groff_font (@MAN5EXT@).
.
.
.command u "n xxx" \[la]white_space\[ra]
Print word with track kerning.
.
This is the same as the
.B t
command except that after printing each character, the current
horizontal position is increased by the sum of the width of that
character and\~\c
.argument n
(an integer in
basic units\~\c
.unit u ).
This command is a groff extension; it is only used for devices whose
.I DESC
file contains the
.B tcommand
keyword; see
.BR groff_font (@MAN5EXT@).
.
.
.command V n
Move down to the absolute vertical position\~\c
.argument n
(a non-negative integer in basic units\~\c
.unit u )
relative to upper edge of current page.
.
.
.command v n
Move
.argument n
basic units\~\c
.unit u
down
.RI ( n
is a non-negative integer).
.
.I [54]
allows negative values for
.I n
also, but
.I groff
doesn't use this.
.
.
.command w
Informs about a paddable whitespace to increase readability.
.
The spacing itself must be performed explicitly by a move command.
.
.
.\" --------------------------------------------------------------------
.SS "Graphics Commands"
.\" --------------------------------------------------------------------
.
Each graphics or drawing command in the intermediate output starts
with the letter\~\c
.B D
followed by one or two characters that specify a subcommand; this
is followed by a fixed or variable number of integer arguments that
are separated by a single space character.
.
A
.BR D \ command
may not be followed by another command on the same line
(apart from a comment), so each
.BR D \ command
is terminated by a syntactical line break.
.
.P
.I troff
output follows the classical spacing rules (no space between command
and subcommand, all arguments are preceded by a single space
character), but the parser allows optional space between the command
letters and makes the space before the first argument optional.
.
As usual, each space can be any sequence of tab and space characters.
.
.P
Some graphics commands can take a variable number of arguments.
.
In this case, they are integers representing a size measured in basic
units\~\c
.unit u .
.
The arguments called
.list1..n h
stand for horizontal distances where positive means right, negative
left.
.
The arguments called
.list1..n v
stand for vertical distances where positive means down, negative up.
.
All these distances are offsets relative to the current location.
.
.P
Unless indicated otherwise, each graphics command directly corresponds
to a similar
.I groff
.B \*[@backslash]D
escape sequence; see
.BR groff (@MAN7EXT@).
.
.P
Unknown D\~commands are assumed to be device-specific.
.
Its arguments are parsed as strings; the whole information is then
sent to the postprocessor.
.
.P
In the following command reference, the syntax element
.I \[la]line_break\[ra]
means a
.I syntactical line break
as defined in section
.BR Separation .
.
.
.D-multiarg ~
Draw B-spline from current position to offset
.indexed_offset h 1 v 1 ,
then to offset
.indexed_offset h 2 v 2
if given, etc.\& up to
.indexed_offset h n v n .
This command takes a variable number of argument pairs;
the current position is moved to the terminal point of the drawn curve.
.
.
.Da-command
Draw arc from current position to
.indexed_offset h 1 v 1 \|+\|\c
.indexed_offset h 2 v 2
with center at
.indexed_offset h 1 v 1 ;
then move the current position to the final point of the arc.
.
.
.D-command C d
.D-command+ C d dummy_arg
Draw a solid circle using the current fill color with diameter\~\c
.argument d
(integer in basic units\~\c
.unit u )
with leftmost point at the current position; then move the current
position to the rightmost point of the circle.
.
An optional second integer argument is ignored (this allows to the
formatter to generate an even number of arguments).
.
This command is a groff extension.
.
.
.D-command c d
Draw circle line with diameter\~\c
.argument d
(integer in basic units\~\c
.unit u )
with leftmost point at the current position; then move the current
position to the rightmost point of the circle.
.
.
.D-command E "h v"
Draw a solid ellipse in the current fill color with a horizontal
diameter of\~\c
.argument h
and a vertical diameter of\~\c
.argument v
(both integers in basic units\~\c
.unit u )
with the leftmost point at the current position; then move to the
rightmost point of the ellipse.
.
This command is a groff extension.
.
.
.D-command e "h v"
Draw an outlined ellipse with a horizontal diameter of\~\c
.argument h
and a vertical diameter of\~\c
.argument v
(both integers in basic units\~\c
.unit u )
with the leftmost point at current position; then move to the
rightmost point of the ellipse.
.
.
.D-command F "color_scheme \f[R][\f[]component .\|.\|.\f[R]]\f[]"
Set fill color for solid drawing objects using different color
schemes; the analoguous command for setting the color of text, line
graphics, and the outline of graphic objects is
.BR m .
.
The color components are specified as integer arguments between 0 and
\n[@maxcolor].
.
The number of color components and their meaning vary for the
different color schemes.
.
These commands are generated by the groff escape sequences
.B \*[@backslash]D'F\ .\|.\|.'
and
.B \*[@backslash]M
(with no other corresponding graphics commands).
.
No position changing.
.
This command is a groff extension.
.
.
.RS
.
.D-command Fc "cyan magenta yellow"
Set fill color for solid drawing objects using the CMY color scheme,
having the 3\~color components cyan, magenta, and yellow.
.
.
.D-command Fd
Set fill color for solid drawing objects to the default fill color value
(black in most cases).
.
No component arguments.
.
.
.D-command Fg "gray"
Set fill color for solid drawing objects to the shade of gray given by
the argument, an integer between 0 (black) and \n[@maxcolor] (white).
.
.
.D-command Fk "cyan magenta yellow black"
Set fill color for solid drawing objects using the CMYK color scheme,
having the 4\~color components cyan, magenta, yellow, and black.
.
.D-command Fr "red green blue"
Set fill color for solid drawing objects using the RGB color scheme,
having the 3\~color components red, green, and blue.
.
.RE
.
.
.D-command f n
The argument
.argument n
must be an integer in the range -32767 to 32767.
.
.RS
.TP
.RI "0 \[<=] " n " \[<=] 1000"
Set the color for filling solid drawing objects to a shade of gray,
where 0 corresponds to solid white, 1000 (the default) to solid black,
and values in between to intermediate shades of gray; this is
obsoleted by command
.BR DFg .
.
.TP
.IR n " < 0 or " n " > 1000"
Set the filling color to the color that is currently being used for
the text and the outline, see command
.BR m .
For example, the command sequence
.
.nf
.ft CB
.RS
.RS
mg 0 0 \n[@maxcolor]
Df -1
.RE
.ft
.fi
.
sets all colors to blue.
.RE
.
.P
No position changing.
.
This command is a groff extension.
.
.RE
.
.
.D-command l "h v"
Draw line from current position to offset
.offset h v
(integers in basic units\~\c
.unit u );
then set current position to the end of the drawn line.
.
.
.D-multiarg p
Draw a polygon line from current position to offset
.offset h1 v1 ,
from there to offset
.offset h2 v2 ,
etc.\& up to offset
.offset hn vn ,
and from there back to the starting position.
.
.ie (\n[@STUPID_DRAWING_POSITIONING] == 1) \{\
For historical reasons, the position is changed by adding the sum of
all arguments with odd index to the actual horizontal position and the
even ones to the vertical position.
.
Although this doesn't make sense it is kept for compatibility.
.
\}
.el \{\
As the polygon is closed, the end of drawing is the starting point, so
the position doesn't change.
\}
.
This command is a groff extension.
.
.
.D-multiarg P
The same macro as the corresponding
.B Dp
command with the same arguments, but draws a solid polygon in the
current fill color rather than an outlined polygon.
.
.ie (\n[@STUPID_DRAWING_POSITIONING] == 1) \{\
The position is changed in the same way as with
.BR Dp .
\}
.el \
No position changing.
.
This command is a groff extension.
.
.
.D-command t n
Set the current line thickness to\~\c
.argument n
(an integer in basic units\~\c
.unit u )
if
.argument n >0;
if
.argument n =0
select the smallest available line thickness; if
.argument n <0
set the line thickness proportional to the point size (this is the
default before the first
.B Dt
command was specified).
.
.ie (\n[@STUPID_DRAWING_POSITIONING] == 1) \{\
For historical reasons, the horizontal position is changed by adding
the argument to the actual horizontal position, while the vertical
position is not changed.
.
Although this doesn't make sense it is kept for compatibility.
.
\}
.el \
No position changing.
.
This command is a groff extension.
.
.
.\" --------------------------------------------------------------------
.SS "Device Control Commands"
.\" --------------------------------------------------------------------
.
Each device control command starts with the letter
.B x
followed by a space character (optional or arbitrary space/\:tab in
groff) and a subcommand letter or word; each argument (if any) must be
preceded by a syntactical space.
.
All
.B x
commands are terminated by a
.IR "syntactical line break" ;
no device control command can be followed by another command on the same
line (except a comment).
.
.P
The subcommand is basically a single letter, but to increase
readability, it can be written as a word, i.e.\& an arbitrary sequence
of characters terminated by the next tab, space, or newline character.
.
All characters of the subcommand word but the first are simply ignored.
.
For example,
.I troff
outputs the initialization command
.B x\ i
as
.B x\ init
and the resolution command
.B x\ r
as
.BR "x\ res" .
.
But writings like
.B x\ i_like_groff
and
.B x\ roff_is_groff
resp.\& are accepted as well to mean the same commands.
.
.P
In the following, the syntax element
.I \[la]line_break\[ra]
means a
.I syntactical line break
as defined in section
.BR Separation .
.
.x-command F name
.xsub Filename
Use
.argument name
as the intended name for the current file in error reports.
.
This is useful for remembering the original file name when groff uses
an internal piping mechanism.
.
The input file is not changed by this command.
.
This command is a groff extension.
.
.
.x-command f "n\ s"
.xsub font
Mount font position\~\c
.argument n
(a non-negative integer) with font named\~\c
.argument s
(a text word),
cf.
.BR groff_font (@MAN5EXT@).
.
.
.x-command H n
.xsub Height
Set character height to\~\c
.argument n
(a positive integer in scaled points\~\c
.unit z ).
.
Classical troff used the unit
points (\c
.unit p )
instead; see section
.BR COMPATIBILITY .
.
.
.x-command i
.xsub init
Initialize device.
.
This is the third command of the prologue.
.
.
.x-command p
.xsub pause
Parsed but ignored.
.
The classical documentation reads
.I pause device, can be
.IR restarted .
.
.
.x-command r "n\ h\ v"
.xsub resolution
Resolution is\~\c
.argument n ,
while
.argument h
is the minimal horizontal motion, and
.argument v
the minimal vertical motion possible with this device; all arguments
are positive integers in basic units\~\c
.unit u
per inch.
.
This is the second command of the prologue.
.
.
.x-command S n
.xsub Slant
Set slant to\~\c
.argument n
degrees (an integer in basic units\~\c
.unit u ).
.
.
.x-command s
.xsub stop
Terminates the processing of the current file; issued as the last
command of any intermediate troff output.
.
.
.x-command t
.xsub trailer
Generate trailer information, if any.
.
In
.IR groff ,
this is actually just ignored.
.
.
.x-command T xxx
.xsub Typesetter
Set name of device to word
.argument xxx ,
a sequence of characters ended by the next whitespace character.
.
The possible device names coincide with those from the groff
.B -T
option.
.
This is the first command of the prologue.
.
.
.x-command u n
.xsub underline
Configure underlining of spaces.
.
If
.argument n
is\~1, start underlining of spaces;
if
.argument n
is\~0, stop underlining of spaces.
.
This is needed for the
.B cu
request in
.I nroff
mode and is ignored otherwise.
.
This command is a groff extension.
.
.
.x-command X anything
.xsub X-escape
Send string
.argument anything
uninterpreted to the device.
.
If the line following this command starts with a
.B +
character this line is interpreted as a continuation line in the
following sense.
.
The
.B +
is ignored, but a newline character is sent instead to the device, the
rest of the line is sent uninterpreted.
.
The same applies to all following lines until the first character of a
line is not a
.B +
character.
.
This command is generated by the
.I groff
escape sequence
.BR \*[@backslash]X .
.
The line-continuing feature is a groff extension.
.
.
.\" --------------------------------------------------------------------
.SS "Obsolete Command"
.\" --------------------------------------------------------------------
.
In
.I classical troff
output, the writing of a single character was mostly done by a very
strange command that combined a horizontal move and the printing of a
character.
.
It didn't have a command code, but is represented by a 3-character
argument consisting of exactly 2\~digits and a character.
.
.TP
.argument ddc
Move right
.argument dd
(exactly two decimal digits) basic units\~\c
.unit u ,
then print character\~\c
.argument c .
.
.RS
.P
In groff, arbitrary syntactical space around and within this command
is allowed to be added.
.
Only when a preceding command on the same line ends with an argument
of variable length a separating space is obligatory.
.
In
.I classical
.IR troff ,
large clusters of these and other commands were used, mostly without
spaces; this made such output almost unreadable.
.
.RE
.
.P
For modern high-resolution devices, this command does not make sense
because the width of the characters can become much larger than two
decimal digits.
.
In groff, this is only used for the devices
.BR X75 ,
.BR X75-12 ,
.BR X100 ,
and
.BR X100-12 .
.
For other devices,
the commands
.B t
and\~\c
.B u
provide a better functionality.
.
.
.\" --------------------------------------------------------------------
.SH "POSTPROCESSING"
.\" --------------------------------------------------------------------
.
The
.I roff
postprocessors are programs that have the task to translate the
intermediate output into actions that are sent to a device.
.
A device can be some piece of hardware such as a printer, or a software
file format suitable for graphical or text processing.
.
The
.I groff
system provides powerful means that make the programming of such
postprocessors an easy task.
.P
There is a library function that parses the intermediate output and
sends the information obtained to the device via methods of a class
with a common interface for each device.
.
So a
.I groff
postprocessor must only redefine the methods of this class.
.
For details, see the reference in section
.BR FILES .
.
.
.\" --------------------------------------------------------------------
.SH "EXAMPLES"
.\" --------------------------------------------------------------------
.
This section presents the intermediate output generated from the same
input for three different devices.
.
The input is the sentence
.I hell world
fed into groff on the command line.
.
.Topic
High-resolution device
.I ps
.
.RS
.
.P
.ShellCommand echo "hell world" | groff -Z -T ps
.
.P
.nf
.ft CB
x T ps
x res 72000 1 1
x init
p1
x font 5 TR
f5
s10000
V12000
H72000
thell
wh2500
tw
H96620
torld
n12000 0
x trailer
V792000
x stop
.ft P
.fi
.RE
.
.P
This output can be fed into the postprocessor
.BR grops (@MAN1EXT@)
to get its representation as a PostScript file.
.
.
.Topic
Low-resolution device
.I latin1
.
.RS
.
.P
This is similar to the high-resolution device except that the
positioning is done at a minor scale.
.
Some comments (lines starting with
.IR # )
were added for clarification; they were not generated by the
formatter.
.
.P
.ShellCommand echo "hell world" | groff -Z -T latin1
.
.P
.nf
.I # prologue
.ft CB
x T latin1
x res 240 24 40
x init
.I # begin a new page
.ft CB
p1
.I # font setup
.ft CB
x font 1 R
f1
s10
.I # initial positioning on the page
.ft CB
V40
H0
.I # write text `hell'
.ft CB
thell
.I # inform about a space, and do it by a horizontal jump
.ft CB
wh24
.I # write text `world'
.ft CB
tworld
.I # announce line break, but do nothing because ...
.ft CB
n40 0
.I # ... the end of the document has been reached
.ft CB
x trailer
V2640
x stop
.ft P
.fi
.RE
.
.P
This output can be fed into the postprocessor
.BR grotty (@MAN1EXT@)
to get a formatted text document.
.
.
.Topic
Classical style output
.
.RS
.
.P
As a computer monitor has a very low resolution compared to modern
printers the intermediate output for the X\~devices can use the
jump-and-write command with its 2-digit displacements.
.
.P
.ShellCommand echo "hell world" | groff -Z -T X100
.
.P
.nf
.ft CB
x T X100
x res 100 1 1
x init
p1
x font 5 TR
f5
s10
V16
H100
.I # write text with old-style jump-and-write command
.ft CB
ch07e07l03lw06w11o07r05l03dh7
n16 0
x trailer
V1100
x stop
.ft P
.fi
.RE
.
.P
This output can be fed into the postprocessor
.BR xditview (1x)
or
.BR gxditview (@MAN1EXT@)
for displaying in\~X.
.
.P
Due to the obsolete jump-and-write command, the text clusters in the
classical output are almost unreadable.
.
.
.\" --------------------------------------------------------------------
.SH "COMPATIBILITY"
.\" --------------------------------------------------------------------
.
The intermediate output language of the 
.I classical troff
was first documented in
.IR [97] .
.
The
.I groff
intermediate output format is compatible with this specification
except for the following features.
.Topic
The classical quasi device independence is not yet implemented.
.
.Topic
The old hardware was very different from what we use today.
.
So the groff devices are also fundamentally different from the ones in
classical troff.
.
For example, the classical PostScript device was called
.I post
and had a resolution of 720 units per inch,
while groff's
.I ps
device has a resolution of 72000 units per inch.
.
Maybe, by implementing some rescaling mechanism similar to the
classical quasi device independence, these could be integrated into
modern groff.
.
.Topic
The B-spline command
.B D~
is correctly handled by the intermediate output parser, but the
drawing routines aren't implemented in some of the postprocessor
programs.
.Topic
The argument of the commands
.B s
and
.B x H
has the implicit unit scaled point\~\c
.unit z
in groff, while classical troff had point (\c
.unit p ).
.
This isn't an incompatibility, but a compatible extension,
for both units coincide for all devices without a
.I sizescale
parameter, including all classical and the groff text devices.
.
The few groff devices with a sizescale parameter either did
not exist, had a different name, or seem to have had a different
resolution.
.
So conflicts with classical devices are very unlikely.
.
.ie (\n[@STUPID_DRAWING_POSITIONING] == 1) \{\
.Topic
The position changing after the commands
.BR Dp ,
.BR DP ,
and
.B Dt
is illogical, but as old versions of groff used this feature it is
kept for compatibility reasons.
.\}             \" @STUPID_DRAWING_POSITIONING
.el \{\
.Topic
Temporarily, there existed some confusion on the positioning after the
.B D
commands that are groff extensions.
.
This has been clarified by establishing the classical rule for all
groff drawing commands:
.
.RS
.P
.I The position after a graphic object has been drawn is at its end;
.I for circles and ellipses, the "end" is at the right side.
.RE
.
.P
From this, the positionings specified for the drawing commands above
follow quite naturally.
.\}             \" @STUPID_DRAWING_POSITIONING
.
.P
The differences between groff and classical troff are documented in
.BR groff_diff (@MAN7EXT@).
.
.
.\" --------------------------------------------------------------------
.SH "FILES"
.\" --------------------------------------------------------------------
.
.TP
.BI @FONTDIR@/dev name /DESC
Device description file for device
.IR name .
.
.TP
.IB \[la]groff_source_dir\[ra] /src/libs/libdriver/input.cpp
Defines the parser and postprocessor for the intermediate output.
.
It is located relative to the top directory of the
.I groff
source tree, e.g.
.IR @GROFFSRCDIR@ .
.
This parser is the definitive specification of the
.I groff
intermediate output format.
.
.
.\" --------------------------------------------------------------------
.SH "SEE ALSO"
.\" --------------------------------------------------------------------
.
A reference like
.BR groff (@MAN7EXT@)
refers to a manual page; here
.I groff
in section\~\c
.I @MAN7EXT@
of the man-page documentation system.
.
To read the example, look up section\~@MAN7EXT@ in your desktop help
system or call from the shell prompt
.
.RS
.P
.ShellCommand man @MAN7EXT@ groff
.RE
.
.P
For more details, see
.BR man (1).
.
.TP
.BR groff (@MAN1EXT@)
option
.B -Z
and further readings on groff.
.
.TP
.BR groff (@MAN7EXT@)
for details of the
.I groff
language such as numerical units and escape sequences.
.
.TP
.BR groff_font (@MAN5EXT@)
for details on the device scaling parameters of the
.B DESC
file.
.
.TP
.BR troff (@MAN1EXT@)
generates the device-independent intermediate output.
.
.TP
.BR roff (@MAN7EXT@)
for historical aspects and the general structure of roff systems.
.
.TP
.BR groff_diff (@MAN7EXT@)
The differences between the intermediate output in groff and classical
troff.
.
.P
.BR \%grodvi (@MAN1EXT@),
.BR \%grohtml (@MAN1EXT@),
.BR \%grolbp (@MAN1EXT@),
.BR \%grolj4 (@MAN1EXT@),
.BR \%grops (@MAN1EXT@),
.BR \%grotty (@MAN1EXT@)
.br
.RS
the groff postprocessor programs.
.RE
.
.P
For a treatment of all aspects of the groff system within a single
document, see the
.I groff info
.IR file .
.
It can be read within the integrated help systems, within
.BR emacs (1)
or from the shell prompt by
.
.RS
.ShellCommand info groff
.RE
.
.P
The
.I classical troff output language
is described in two AT&T Bell Labs CSTR documents available on-line at
.URL http://\:cm.bell-labs.com/\:cm/\:cs/\:cstr.html \
     "Bell Labs CSTR site" .
.
.TP
.I [CSTR #97]
.I A Typesetter-independent TROFF
by
.I Brian Kernighan
is the original and most concise documentation on the output language;
see
.URL http://\:cm.bell-labs.com/\:cm/\:cs/\:cstr/\:97.ps.gz CSTR\~#97 .
.
.TP
.I [CSTR\~#54]
The 1992 revision of the
.I Nroff/\:Troff User's Manual
by
.I J.\& F.\& Osanna
and
.I Brian Kernighan
isn't as concise as
.I [CSTR\~#97]
regarding the output language;
see
.URL http://\:cm.bell-labs.com/\:cm/\:cs/\:cstr/\:54.ps.gz CSTR\~#54 .
.
.
.\" --------------------------------------------------------------------
.SH "AUTHORS"
.\" --------------------------------------------------------------------
.
Copyright (C) 1989, 2001, 2002, 2003 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 with this package; it is also
available on-line at the
.URL http://\:www.gnu.org/\:copyleft/\:fdl.html "GNU copyleft site" .
.
.P
This document is part of
.IR groff ,
the GNU roff distribution.
.
It is based on a former version \- published under the GPL \- that
described only parts of the
.I groff
extensions of the output language.
.
It has been rewritten 2002 by
.MTO bwarken@mayn.de "Bernd Warken"
and is maintained by
.MTO wl@gnu.org "Werner Lemberg" .
.
.\" --------------------------------------------------------------------
.\" Emacs settings
.\" --------------------------------------------------------------------
.\"
.\" Local Variables:
.\" mode: nroff
.\" End: