Provided by: groff_1.21-7_i386 bug

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-
       specific 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
       system.   The  groff  program  provides  the  option  -Z   to   inhibit
       postprocessing,  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
       postprocessors.   This  parser  is smarter on whitespace and implements
       obsolete 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
       completely different from  the  groff(7)  language.   While  the  groff
       language  is a high-level programming language for text processing, the
       intermediate output language is a kind of low-level assembler  language
       by specifying all positions on the page for writing and drawing.

       The  pre-groff  roff  versions  are  denoted  as  classical troff.  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
       information  on what has to be printed at what position on the intended
       device.  So the language of the intermediate output format can be quite
       small.   Its  only elements are commands with or without arguments.  In
       this document, the term "command" always  refers  to  the  intermediate
       output   language,  never  to  the  roff  language  used  for  document
       formatting.  There are commands for positioning and text  writing,  for
       drawing, and for device controlling.

   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
       syntactical  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
       character.

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

       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 split 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
       values 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 (this is, glyphs).  The names  of
       glyphs  and  fonts  can  be of arbitrary length.  A glyph 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
       command.

   Document Parts
       A  correct  intermediate  output  document  consists  of two parts, the
       prologue 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
       Commands.   However,  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.
       Syntactically, 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  command.   Absolute  positioning  (by  the H and V commands) is done
       relative to the current page, all other positioning is done relative to
       the current 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
       integer  arguments would clash or if the preceding argument ends with a
       string argument.

       C xxx<white-space>
              Print a glyph  (special  character)  named  xxx.   The  trailing
              syntactical  space  or  line  break  is necessary to allow glyph
              names of arbitrary length.  The glyph is printed at the  current
              print  position;  the  glyph's  size is read from the font file.
              The print position is not changed.

       c c    Print glyph with single-letter  name  c  at  the  current  print
              position;  the  glyph'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
              generated   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  glyph with index n (an integer, normally non-negative) of
              the current font.   The  print  position  is  not  changed.   If
              -T html or -T xhtml is used, negative values are emitted also to
              indicate an unbreakable space with given  width.   For  example,
              N  -193  represents  an  unbreakable  space which has a width of
              193u.  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
              performing 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 xyz...<white-space>
       t xyz... dummy-arg<white-space>
              Print a word, i.e., a  sequence  of  glyphs  with  single-letter
              names  x,  y, z, etc., 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 glyph should be printed at the current  position,  the
              current  horizontal  position  should  then  be increased by the
              width of the first glyph, and so on for each glyph.  The  widths
              of the glyph are read from the font file, scaled for the current
              point  size,  and  rounded  to  a  multiple  of  the  horizontal
              resolution.  Special characters (glyphs with names longer than a
              single letter) cannot be printed using this command; use  the  C
              command for those glyphs.  This command is a groff extension; it
              is only used for devices whose DESC file contains  the  tcommand
              keyword; see groff_font(5).

       u n xyz...<white-space>
              Print  word  with  track  kerning.   This  is  the same as the t
              command except that  after  printing  each  glyph,  the  current
              horizontal position is increased by the sum of the width of that
              glyph 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
              command.

   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
       subcommand; this is followed by a fixed or variable number  of  integer
       arguments  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
       comment), so each D command is terminated by a syntactical line break.

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

       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 h arguments stand for horizontal distances where positive
       means right,  negative  left.   The  v  arguments  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
       postprocessor.

       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
              generated  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 inbetween 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
              reasons, the position is  changed  by  adding  the  sum  of  all
              arguments  with  odd index to the actual horizontal position and
              the even ones to the vertical position.  Although  this  doesn't
              make  sense  it  is  kept  for compatibility.  This command is a
              groff extension.

       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
              position,  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
       subcommand 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
       readability,  it  can be written as a word, i.e., an arbitrary sequence
       of characters terminated by the next tab, space, or newline  character.
       All characters of the subcommand word but the first are simply ignored.
       For example, 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 are accepted as well to mean the same commands.

       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
              arguments 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
              actually 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
              otherwise.  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, emitting a single glyph was mostly done by a
       very strange command that combined a horizontal move and  the  printing
       of  a  glyph.   It  didn't have a command code, but is represented 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 glyph with single-letter name 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
              separating 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 glyphs 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
       system provides powerful  means  that  make  the  programming  of  such
       postprocessors 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
       reference 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
       representation as a PostScript file.

       o Low-resolution device latin1

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

         shell> "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
       formatted 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> "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
       documented  in  [CSTR  #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
         classical 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
         implementing  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
         output 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
         classical and the groff text devices.  The few groff devices  with  a
         sizescale  parameter  either  did not exist, had a different name, or
         seem to have had a different resolution.  So conflicts with classical
         devices are very unlikely.

       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
         compatibility reasons.

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

FILES

       /usr/share/groff/1.21/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
              output.   It  is  located  relative  to the top directory of the
              groff source tree.  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
       section 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
              systems.

       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
       document, 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
              original and most  comprehensive  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.
              Ossanna and Brian Kernighan isn't as comprehensive 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, 2005, 2006, 2007, 2008,
       2009 Free Software Foundation, Inc.

       This document is distributed under the  terms  of  the  FDL  (GNU  Free
       Documentation  License) version 1.3 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 was rewritten
       in  2002  by  Bernd  Warken  and  is  maintained  by   Werner   Lemberg
       <wl@gnu.org>.