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GROFF_OUT(5)							  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 groff(1).	 This output is	produced by  a
       run  of	the GNU	troff(1) program.  It contains already all device-spe-
       cific information, but it is not	yet 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.
       Both formats can	be viewed directly with	gxditview(1).

       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 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 pre-groff roff versions are denoted as classical troff.  The	inter-
       mediate 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
       device 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
       positioning 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
       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.

       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
       occur 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
       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	 inte-
       ger  arguments  would  clash  or	 if the	preceding argument ends	with a
       string argument.

       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.   [CSTR  #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 (an integer,	normally non-negative)
	      of  the  current	font.	The print position is not changed.  If
	      -T html is used, negative	values are emitted also	to indicate an
	      unbreakable  space with given width.  For	example, N -193	repre-
	      sents an unbreakable space which has a width of 193u.  This com-
	      mand 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
	      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 C  com-
	      mand  for	named characters).  This command is a groff extension;
	      it is only used for devices whose	DESC file contains  the	 tcom-
	      mand keyword; 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).
	      [CSTR  #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
	      arguments).  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
	      basic  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,
		     magenta, and yellow.

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

	      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,
		     magenta, 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
		     being 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
	      arguments,  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 char-
       acters 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
	      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.

       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
	      device, 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 degrees (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
	      coincide 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
	      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	+ character.  This command is generated	by the
	      groff escape sequence \X.	  The  line-continuing	feature	 is  a
	      groff extension.

   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
       device  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 [CSTR #97].  The groff	intermediate output format is compati-
       ble 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
	 device	 has  a	 resolution of 72000 units per inch.  Maybe, by	imple-
	 menting 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/share/groff_font/devname/DESC
	      Device description file for device name.

       _groff_source_dir_/src/libs/libdriver/input.cpp
	      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.

       gxditview(1)
	      Viewer for the intermediate output.

       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.
	      Osanna and Brian	Kernighan  isn't  as  concise  as  [CSTR  #97]
	      regarding	the output language; see CSTR #54 <http://
	      cm.bell-labs.com/cm/cs/cstr/54.ps.gz>.

AUTHORS
       Copyright (C) 1989, 2001, 2002, 2003, 2004  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  and is maintained by	Werner Lemberg
       <wl@gnu.org>.

Groff Version 1.19.2		16 January 2014			  GROFF_OUT(5)

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

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