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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.	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
       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 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
       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.  [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
	      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).	  [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 h1, h2,  ...,  hn	 stand
       for  horizontal	distances  where  positive means right, negative left.
       The arguments called v1, v2, ..., vn 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 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
	      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 (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.

       · 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
	 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.

       · 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/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.
	      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 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		   Nov	2003			  GROFF_OUT(5)
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