Provided by: groff_1.18.1.1-16_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.  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
       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.  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
       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 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 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
       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.  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
       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.  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.
       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
       #anythingend_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  special  groff  character  named  xxx.   The  trailing
              syntactical  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
              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 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
              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 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
              command  for  named  characters).   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 xxx〈white_space〉
              Print word with track kerning.   This  is  the  same  as  the  t
              command  except  that after printing each character, the current
              horizontal 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
              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 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
       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 \DF ...’  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
              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  resp.  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 (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, 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
       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 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
              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 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
       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.

       · 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.

       · 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> 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
       formatted 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
       documented 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
         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.

       · 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.

       · 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.

       · 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/1.18.1/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
              output.   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
       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.

       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 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  Users  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
       Documentation 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〉.