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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  postpro-
       cessors 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.

       o 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.

       o 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.

       o 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.

       o The classical quasi device independence is not	yet implemented.

       o 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.

       o 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.

       o 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.

       o 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	       28 February 2021			  GROFF_OUT(5)

NAME | DESCRIPTION | LANGUAGE CONCEPTS | COMMAND REFERENCE | POSTPROCESSING | EXAMPLES | COMPATIBILITY | FILES | SEE ALSO | AUTHORS

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