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GROFF_OUT(5)		      File Formats Manual		  GROFF_OUT(5)

NAME
       groff_out - groff intermediate output format

DESCRIPTION
       This  manual  page  describes the intermediate output format of the GNU
       roff(7) text processing system.	This output is produced	by  a  run  of
       the  GNU	 troff(1) program before it is fed into	a device postprocessor
       program.

       As the GNU roff processor groff(1) is a wrapper	program	 around	 troff
       that  automatically calls a postprocessor, this output does not show up
       normally.  This is why it is called intermediate	within the groff  sys-
       tem.   The groff	program	provides the option -Z to inhibit postprocess-
       ing, such that the produced intermediate	output	is  sent  to  standard
       output just like	calling	troff manually.

       In this document, the term troff	output describes what is output	by the
       GNU  troff  program,  while  intermediate output	refers to the language
       that is accepted	by the parser that prepares this output	for the	 post-
       processors.   This parser is smarter on whitespace and implements obso-
       lete elements for compatibility,	otherwise both formats are  the	 same.
       The pre-groff roff versions are denoted as classical troff.

       The  main  purpose  of the intermediate output concept is to facilitate
       the development of postprocessors by providing a	common programming in-
       terface for all devices.	 It has	a language of its  own	that  is  com-
       pletely different from the groff(7) language.  While the	groff language
       is  a high-level	programming language for text processing, the interme-
       diate output language is	a kind	of  low-level  assembler  language  by
       specifying all positions	on the page for	writing	and drawing.

       The  intermediate  output  produced  by groff is	fairly readable, while
       classical troff output was hard to understand because of	strange	habits
       that are	still supported, but not used any longer by GNU	troff.

LANGUAGE CONCEPTS
       During the run of troff,	the roff input is cracked down to the informa-
       tion 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 doc-
       ument, the term "command" always	refers to the intermediate output lan-
       guage,  never to	the roff language used for document formatting.	 There
       are commands for	positioning and	text writing, for drawing, and for de-
       vice controlling.

   Separation
       Classical troff output had strange  requirements	 on  whitespace.   The
       groff  output  parser,  however,	is smart about whitespace by making it
       maximally optional.  The	whitespace characters, i.e.  the  tab,	space,
       and  newline  characters,  always have a	syntactical meaning.  They are
       never printable because spacing within the output is always done	by po-
       sitioning commands.

       Any sequence of space or	tab characters is treated as a single  syntac-
       tical space.  It	separates commands and arguments, but is only required
       when  there would occur a clashing between the command code and the ar-
       guments 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.

       A line break is a syntactical element, too.  Every command argument can
       be  followed  by	whitespace, a comment, or a newline character.	Thus a
       syntactical line	break is defined to consist  of	 optional  syntactical
       space  that  is optionally followed by a	comment, and a newline charac-
       ter.

       The normal commands, those for positioning and text, consist of a  sin-
       gle letter taking a fixed number	of arguments.  For historical reasons,
       the  parser  allows to stack such commands on the same line, but	fortu-
       nately, in groff	intermediate output, every command with	at  least  one
       argument	 is  followed  by a line break,	thus providing excellent read-
       ability.

       The other commands -- those for drawing and device controlling --  have
       a  more	complicated  structure;	some recognize long command names, and
       some take a variable number of arguments.  So all D and x commands were
       designed	to request a syntactical line break after their	last argument.
       Only one	command, `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.

       Empty lines, i.e. lines containing only space and/or a comment, can oc-
       cur everywhere.	They are just ignored.

   Argument Units
       Some commands take integer arguments that are assumed to	represent val-
       ues  in	a measurement unit, but	the letter for the corresponding scale
       indicator is  not  written  with	 the  output  command  arguments;  see
       groff(7)	and the	groff info file	for more on this topic.	 Most commands
       assume the scale	indicator u, the basic unit of the device, some	use z,
       the  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 DESC file; see	groff_font(5).

       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.

       A string	argument is always terminated by the next whitespace character
       (space,	tab,  or newline); an embedded # 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 com-
       mand.

   Document Parts
       A correct intermediate output document consists of two parts, the  pro-
       logue and the body.

       The  task of the	prologue is to set the general device parameters using
       three exactly specified commands.  The groff prologue is	guaranteed  to
       consist of the following	three lines (in	that order):

	      x	T device
	      x	res n h	v
	      x	init

       with  the  arguments set	as outlined in the section Device Control Com-
       mands.  But the parser for the intermediate output format  is  able  to
       swallow additional whitespace and comments as well.

       The body	is the main section for	processing the document	data.  Syntac-
       tically,	 it is a sequence of any commands different from the ones used
       in the prologue.	 Processing is terminated as soon as the first	x stop
       command	is encountered;	the last line of any groff intermediate	output
       always contains such a command.

       Semantically, the body is page oriented.	 A new page is	started	 by  a
       p  command.  Positioning, writing, and drawing commands are always done
       within the current page,	so they	cannot occur before the	first  p  com-
       mand.   Absolute	positioning (by	the H and V commands) is done relative
       to the current page, all	other positioning is done relative to the cur-
       rent location within this page.

COMMAND	REFERENCE
       This section describes all intermediate output commands,	the  classical
       commands	as well	as the groff extensions.

   Comment Command
       #anything<end_of_line>
	      A	comment.  Ignore any characters	from the # character up	to the
	      next newline character.

       This command is the only	possibility for	commenting in the intermediate
       output.	 Each  comment can be preceded by arbitrary syntactical	space;
       every command can be terminated by a comment.

   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, syntactical space	can  be	 inserted  be-
       fore,  after, and between the command letter and	its arguments.	All of
       these commands are stackable, i.e., they	can be preceded	by other  sim-
       ple  commands or	followed by arbitrary other commands on	the same line.
       A separating syntactical	space is only necessary	when two integer argu-
       ments would clash or if the preceding argument ends with	a string argu-
       ment.

       C xxx<white_space>
	      Print a special groff character named xxx.  The trailing syntac-
	      tical 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.

       c c    Print character c	at the current print position; the character's
	      size is read from	the font file.	 The  print  position  is  not
	      changed.

       f n    Set font to font number n	(a non-negative	integer).

       H n    Move  right  to the absolute vertical position n (a non-negative
	      integer in basic units u)	relative to left edge of current page.

       h n    Move n (a	non-negative integer) basic units  u  horizontally  to
	      the  right.   [54]  allows negative values for n also, but groff
	      doesn't use this.

       m color_scheme [component ...]
	      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 DF.  The
	      color components are specified as	integer	 arguments  between  0
	      and  65536.   The	 number	 of color components and their meaning
	      vary for the different color schemes.  These commands are	gener-
	      ated by the groff	escape sequence	 \m.   No  position  changing.
	      These commands are a groff extension.

	      mc cyan magenta yellow
		     Set  color	using the CMY color scheme, having the 3 color
		     components	cyan, magenta, and yellow.

	      md     Set color to the  default	color  value  (black  in  most
		     cases).  No component arguments.

	      mg gray
		     Set  color	to the shade of	gray given by the argument, an
		     integer between 0 (black) and 65536 (white).

	      mk cyan magenta yellow black
		     Set color using the CMYK color scheme, having the 4 color
		     components	cyan, magenta, yellow, and black.

	      mr red green blue
		     Set color using the RGB color scheme, having the 3	 color
		     components	red, green, and	blue.

       N n    Print  character	with  index  n (a non-negative integer)	of the
	      current font.  The print position	is not changed.	 This  command
	      is a groff extension.

       n b a  Inform the device	about a	line break, but	no positioning is done
	      by  this	command.   In classical	troff, the integer arguments b
	      and a informed about the space before and	after the current line
	      to make the intermediate output more human readable without per-
	      forming any action.  In groff, they are just ignored,  but  they
	      must be provided for compatibility reasons.

       p n    Begin  a new page	in the outprint.  The page number is set to 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
	      p	command	must be	issued before any of these commands.

       s n    Set point	size to	n scaled points	(this is unit z	in GNU troff).
	      Classical	troff used the unit points (p)	instead;  see  section
	      COMPATIBILITY.

       t xxx<white_space>
       t xxx dummy_arg<white_space>
	      Print  a word, i.e. a sequence of	characters xxx terminated by a
	      space character or a line	break; an optional second integer  ar-
	      gument 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 C command for
	      named characters).  This command is a  groff  extension;	it  is
	      only used	for devices whose DESC file contains the tcommand key-
	      word; see	groff_font(5).

       u n xxx<white_space>
	      Print  word  with	track kerning.	This is	the same as the	t com-
	      mand except that after printing each character, the current hor-
	      izontal position is increased by the sum of the  width  of  that
	      character	 and n (an integer in basic units u).  This command is
	      a	groff extension; it is only used for devices whose  DESC  file
	      contains the tcommand keyword; see groff_font(5).

       V n    Move  down  to  the absolute vertical position n (a non-negative
	      integer in basic units u)	relative  to  upper  edge  of  current
	      page.

       v n    Move  n  basic units u down (n is	a non-negative integer).  [54]
	      allows negative values for n also, but groff doesn't use this.

       w      Informs about a paddable	whitespace  to	increase  readability.
	      The  spacing  itself must	be performed explicitly	by a move com-
	      mand.

   Graphics Commands
       Each graphics or	drawing	command	in the intermediate output starts with
       the letter D followed by	one or two characters that specify  a  subcom-
       mand;  this  is followed	by a fixed or variable number of integer argu-
       ments that are separated	by a single space character.  A	D command  may
       not  be followed	by another command on the same line (apart from	a com-
       ment), so each D	command	is terminated by a syntactical line break.

       troff output follows the	classical spacing rules	(no space between com-
       mand and	subcommand, all	arguments are preceded by a single space char-
       acter), but the parser allows optional space between the	 command  let-
       ters and	makes the space	before the first argument optional.  As	usual,
       each space can be any sequence of tab and space characters.

       Some  graphics  commands	 can  take a variable number of	arguments.  In
       this case, they are integers representing  a  size  measured  in	 basic
       units  u.   The	arguments  called h1, h2, ..., hn stand	for horizontal
       distances where positive	means right,  negative	left.	The  arguments
       called  v1,  v2,	 ...,  vn  stand for vertical distances	where positive
       means down, negative up.	 All these distances are offsets  relative  to
       the current location.

       Unless  indicated otherwise, each graphics command directly corresponds
       to a similar groff \D escape sequence; see groff(7).

       Unknown D commands are assumed to be  device-specific.	Its  arguments
       are  parsed as strings; the whole information is	then sent to the post-
       processor.

       In the following	command	reference,  the	 syntax	 element  <line_break>
       means a syntactical line	break as defined in section Separation.

       D~ h1 v1	h2 v2 ... hn vn<line_break>
	      Draw  B-spline from current position to offset (h1, v1), then to
	      offset (h2, v2) if given,	etc.  up  to  (hn, vn).	 This  command
	      takes  a variable	number of argument pairs; the current position
	      is moved to the terminal point of	the drawn curve.

       Da h1 v1	h2 v2<line_break>
	      Draw arc from current position to	(h1, v1)+(h2, v2) with	center
	      at  (h1, v1);  then move the current position to the final point
	      of the arc.

       DC d<line_break>
       DC d dummy_arg<line_break>
	      Draw a solid circle using	the current fill color with diameter d
	      (integer in basic	units 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 ar-
	      guments).	 This command is a groff extension.

       Dc d<line_break>
	      Draw circle line with diameter d (integer	in basic units u) with
	      leftmost point at	the current position; then  move  the  current
	      position to the rightmost	point of the circle.

       DE h v<line_break>
	      Draw a solid ellipse in the current fill color with a horizontal
	      diameter of h and	a vertical diameter of v (both integers	in ba-
	      sic  units  u)  with the leftmost	point at the current position;
	      then move	to the rightmost point of the ellipse.	 This  command
	      is a groff extension.

       De h v<line_break>
	      Draw  an	outlined ellipse with a	horizontal diameter of h and a
	      vertical diameter	of v (both integers in basic units u) with the
	      leftmost point at	current	position; then move to	the  rightmost
	      point of the ellipse.

       DF color_scheme [component ...]<line_break>
	      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 m.  The
	      color components are specified as	integer	 arguments  between  0
	      and  65536.   The	 number	 of color components and their meaning
	      vary for the different color schemes.  These commands are	gener-
	      ated by the groff	escape sequences \D'F ...'  and	 \M  (with  no
	      other  corresponding  graphics commands).	 No position changing.
	      This command is a	groff extension.

	      DFc cyan magenta yellow<line_break>
		     Set fill color for	solid drawing objects  using  the  CMY
		     color  scheme,  having  the  3 color components cyan, ma-
		     genta, and	yellow.

	      DFd <line_break>
		     Set fill color for	solid drawing objects to  the  default
		     fill color	value (black in	most cases).  No component ar-
		     guments.

	      DFg gray<line_break>
		     Set  fill color for solid drawing objects to the shade of
		     gray given	by the argument, an integer between 0  (black)
		     and 65536 (white).

	      DFk cyan magenta yellow black<line_break>
		     Set  fill	color for solid	drawing	objects	using the CMYK
		     color scheme, having the 4	 color	components  cyan,  ma-
		     genta, yellow, and	black.

	      DFr red green blue<line_break>
		     Set  fill	color  for solid drawing objects using the RGB
		     color scheme, having the 3	color components  red,	green,
		     and blue.

       Df n<line_break>
	      The argument n must be an	integer	in the range -32767 to 32767.

	      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
		     DFg.

	      n	< 0 or n > 1000
		     Set the filling color to the color	that is	currently  be-
		     ing  used	for  the  text and the outline,	see command m.
		     For example, the command sequence
			    mg 0 0 65536
			    Df -1
		     sets all colors to	blue.

	      No position changing.  This command is a groff extension.

       Dl h v<line_break>
	      Draw line	from current position to offset	 (h, v)	 (integers  in
	      basic  units  u);	 then  set  current position to	the end	of the
	      drawn line.

       Dp h1 v1	h2 v2 ... hn vn<line_break>
	      Draw a polygon line from current position	 to  offset  (h1, v1),
	      from  there  to offset (h2, v2), etc. up to offset (hn, vn), and
	      from there back to the starting position.	 For  historical  rea-
	      sons, 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.  This command is  a	 groff	exten-
	      sion.

       DP h1 v1	h2 v2 ... hn vn<line_break>
	      The same macro as	the corresponding Dp command with the same ar-
	      guments,	but  draws  a  solid polygon in	the current fill color
	      rather than an outlined polygon.	The position is	changed	in the
	      same way as with Dp.  This command is a groff extension.

       Dt n<line_break>
	      Set the current  line  thickness	to  n  (an  integer  in	 basic
	      units  u)	 if  n>0;  if  n=0  select the smallest	available line
	      thickness; if n<0	set the	line  thickness	 proportional  to  the
	      point  size (this	is the default before the first	Dt command was
	      specified).  For historical reasons, the horizontal position  is
	      changed  by  adding  the argument	to the actual horizontal posi-
	      tion, while the vertical position	is not changed.	 Although this
	      doesn't make sense it is kept for	compatibility.	 This  command
	      is a groff extension.

   Device Control Commands
       Each  device  control  command  starts  with the	letter x followed by a
       space character (optional or arbitrary space/tab	in groff) and  a  sub-
       command	letter	or  word; each argument	(if any) must be preceded by a
       syntactical space.  All x commands are terminated by a syntactical line
       break; no device	control	command	can be followed	by another command  on
       the same	line (except a comment).

       The  subcommand is basically a single letter, but to increase readabil-
       ity, it can be written as a word, i.e. an arbitrary sequence of charac-
       ters terminated by the next tab,	 space,	 or  newline  character.   All
       characters  of  the  subcommand	word but the first are simply ignored.
       For example, troff outputs the initialization command x i as x init and
       the resolution command x	r as x res.  But writings like	x i_like_groff
       and  x roff_is_groff  resp.  are	accepted as well to mean the same com-
       mands.

       In the following, the syntax element <line_break> means	a  syntactical
       line break as defined in	section	Separation.

       xF name<line_break>
	      (Filename	control	command)
	      Use  name	as the intended	name for the current file in error re-
	      ports.  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.

       xf n s<line_break>
	      (font control command)
	      Mount font position n (a non-negative integer) with font named s
	      (a text word), cf.  groff_font(5).

       xH n<line_break>
	      (Height control command)
	      Set  character  height  to  n  (a	 positive  integer  in	scaled
	      points z).  Classical troff used the unit	 points	 (p)  instead;
	      see section COMPATIBILITY.

       xi<line_break>
	      (init control command)
	      Initialize device.  This is the third command of the prologue.

       xp<line_break>
	      (pause control command)
	      Parsed but ignored.  The classical documentation reads pause de-
	      vice, can	be restarted.

       xr n h v<line_break>
	      (resolution control command)
	      Resolution is n, while h is the minimal horizontal motion, and v
	      the minimal vertical motion possible with	this device; all argu-
	      ments  are positive integers in basic units u per	inch.  This is
	      the second command of the	prologue.

       xS n<line_break>
	      (Slant control command)
	      Set slant	to n (an integer in basic units	u).

       xs<line_break>
	      (stop control command)
	      Terminates the processing	of the current	file;  issued  as  the
	      last command of any intermediate troff output.

       xt<line_break>
	      (trailer control command)
	      Generate	trailer	 information, if any.  In groff, this is actu-
	      ally just	ignored.

       xT xxx<line_break>
	      (Typesetter control command)
	      Set name of device to word xxx, a	sequence of  characters	 ended
	      by the next whitespace character.	 The possible device names co-
	      incide  with  those from the groff -T option.  This is the first
	      command of the prologue.

       xu n<line_break>
	      (underline control command)
	      Configure	underlining of spaces.	If n is	1,  start  underlining
	      of  spaces;  if  n  is  0,  stop underlining of spaces.  This is
	      needed for the cu	request	in nroff mode and  is  ignored	other-
	      wise.  This command is a groff extension.

       xX anything<line_break>
	      (X-escape	control	command)
	      Send  string  anything uninterpreted to the device.  If the line
	      following	this command starts with a + character	this  line  is
	      interpreted  as a	continuation line in the following sense.  The
	      +	is ignored, but	a newline character is sent instead to the de-
	      vice, the	rest of	the line is sent uninterpreted.	 The same  ap-
	      plies to all following lines until the first character of	a line
	      is  not  a  + character.	This command is	generated by the groff
	      escape sequence \X.  The line-continuing feature is a groff  ex-
	      tension.

   Obsolete Command
       In 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	repre-
       sented  by  a 3-character argument consisting of	exactly	2 digits and a
       character.

       ddc    Move right dd (exactly two decimal digits) basic units  u,  then
	      print character c.

	      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 sep-
	      arating space is obligatory.  In classical troff,	large clusters
	      of  these	 and  other commands were used,	mostly without spaces;
	      this made	such output almost unreadable.

       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  X75,
       X75-12,	X100,  and  X100-12.   For other devices, the commands t and u
       provide a better	functionality.

POSTPROCESSING
       The roff	postprocessors are programs that have the  task	 to  translate
       the  intermediate output	into actions that are sent to a	device.	 A de-
       vice can	be some	piece of hardware such as a  printer,  or  a  software
       file  format suitable for graphical or text processing.	The groff sys-
       tem provides powerful means that	make the  programming  of  such	 post-
       processors an easy task.

       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 groff postprocessor must
       only  redefine  the methods of this class.  For details,	see the	refer-
       ence in section FILES.

EXAMPLES
       This section presents the intermediate output generated from  the  same
       input  for  three  different  devices.	The input is the sentence hell
       world fed into groff on the command line.

        High-resolution device	ps

	 shell>	echo hell world	| groff	-Z -T ps

	 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

       This output can be fed into the postprocessor grops(1) to get its  rep-
       resentation as a	PostScript file.

        Low-resolution	device latin1

	 This  is  similar to the high-resolution device except	that the posi-
	 tioning is done at a minor scale.  Some comments (lines starting with
	 #) were added for clarification; they were not	generated by the  for-
	 matter.

	 shell>	echo hell world	| groff	-Z -T latin1

	 # prologue
	 x T latin1
	 x res 240 24 40
	 x init
	 # begin a new page
	 p1
	 # font	setup
	 x font	1 R
	 f1
	 s10
	 # initial positioning on the page
	 V40
	 H0
	 # write text `hell'
	 thell
	 # inform about	a space, and do	it by a	horizontal jump
	 wh24
	 # write text `world'
	 tworld
	 # announce line break,	but do nothing because ...
	 n40 0
	 # ... the end of the document has been	reached
	 x trailer
	 V2640
	 x stop

       This  output  can be fed	into the postprocessor grotty(1) to get	a for-
       matted text document.

        Classical style output

	 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.

	 shell>	echo hell world	| groff	-Z -T X100

	 x T X100
	 x res 100 1 1
	 x init
	 p1
	 x font	5 TR
	 f5
	 s10
	 V16
	 H100
	 # write text with old-style jump-and-write command
	 ch07e07l03lw06w11o07r05l03dh7
	 n16 0
	 x trailer
	 V1100
	 x stop

       This  output  can  be  fed  into	 the  postprocessor  xditview(1x)   or
       gxditview(1) for	displaying in X.

       Due  to	the  obsolete jump-and-write command, the text clusters	in the
       classical output	are almost unreadable.

COMPATIBILITY
       The intermediate	output language	of the classical troff was first docu-
       mented in [97].	The groff intermediate	output	format	is  compatible
       with this specification except for the following	features.

        The classical quasi device independence is not	yet implemented.

        The  old  hardware was	very different from what we use	today.	So the
	 groff devices are also	fundamentally different	from the ones in clas-
	 sical troff.  For example, the	classical PostScript device was	called
	 post and had a	resolution of 720 units	per inch, while	groff's	ps de-
	 vice has a resolution of 72000	units per inch.	 Maybe,	by  implement-
	 ing  some  rescaling  mechanism similar to the	classical quasi	device
	 independence, these could be integrated into modern groff.

        The B-spline command D~ is correctly handled by the intermediate out-
	 put parser, but the drawing routines aren't implemented  in  some  of
	 the postprocessor programs.

        The  argument	of the commands	s and x	H has the implicit unit	scaled
	 point z in groff, while classical troff had point (p).	 This isn't an
	 incompatibility, but a	compatible extension, for both units  coincide
	 for  all devices without a sizescale parameter, including all classi-
	 cal 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.

        The position changing after the commands Dp, DP, and Dt is illogical,
	 but as	old versions of	groff used this	feature	it is kept for compat-
	 ibility reasons.

       The differences between groff and classical  troff  are	documented  in
       groff_diff(7).

FILES
       /usr/local/share/groff/1.18.1/font/devname/DESC
	      Device description file for device name.

       <groff_source_dir>/src/libs/libdriver/input.cc
	      Defines  the  parser and postprocessor for the intermediate out-
	      put.  It is located relative to the top directory	of  the	 groff
	      source tree, e.g.	 @GROFFSRCDIR@.	 This parser is	the definitive
	      specification of the groff intermediate output format.

SEE ALSO
       A  reference  like groff(7) refers to a manual page; here groff in sec-
       tion 7 of the man-page documentation system.  To	read the example, look
       up section 7 in your desktop help system	or call	from the shell prompt

	      shell> man 7 groff

       For more	details, see man(1).

       groff(1)
	      option -Z	and further readings on	groff.

       groff(7)
	      for details of the groff language	such as	 numerical  units  and
	      escape sequences.

       groff_font(5)
	      for details on the device	scaling	parameters of the DESC file.

       troff(1)
	      generates	the device-independent intermediate output.

       roff(7)
	      for  historical  aspects	and the	general	structure of roff sys-
	      tems.

       groff_diff(7)
	      The differences between the intermediate	output	in  groff  and
	      classical	troff.

       grodvi(1), grohtml(1), grolbp(1), grolj4(1), grops(1), grotty(1)
	      the groff	postprocessor programs.

       For a treatment of all aspects of the groff system within a single doc-
       ument,  see  the	groff info file.  It can be read within	the integrated
       help systems, within emacs(1) or	from the shell prompt by
	      shell> info groff

       The classical troff output language is described	in two AT&T Bell  Labs
       CSTR documents available	on-line	at Bell	Labs CSTR site <http://
       cm.bell-labs.com/cm/cs/cstr.html>.

       [CSTR #97]
	      A	 Typesetter-independent	TROFF by Brian Kernighan is the	origi-
	      nal and most concise documentation on the	output language; see
	      CSTR #97 <http://cm.bell-labs.com/cm/cs/cstr/97.ps.gz>.

       [CSTR #54]
	      The 1992 revision	of the Nroff/Troff User's Manual by J. F.  Os-
	      anna  and	Brian Kernighan	isn't as concise as [CSTR #97] regard-
	      ing the output language; see CSTR	#54 <http://cm.bell-labs.com/
	      cm/cs/cstr/54.ps.gz>.

AUTHORS
       Copyright (C) 1989, 2001, 2002 Free Software Foundation,	Inc.

       This document is	distributed under the terms of the FDL (GNU Free Docu-
       mentation 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
       GNU copyleft site <http://www.gnu.org/copyleft/fdl.html>.

       This document is	part of	groff, the GNU roff distribution.  It is based
       on  a  former  version  - published under the GPL - that	described only
       parts of	the groff extensions of	the  output  language.	 It  has  been
       rewritten  2002	by Bernd Warken	<bwarken@mayn.de> and is maintained by
       Werner Lemberg <wl@gnu.org>.

Groff Version 1.18.1		 12 April 2025			  GROFF_OUT(5)

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