GROFF_OUT(5)                                                      GROFF_OUT(5)



NAME
       groff_out - groff intermediate output format

DESCRIPTION
       This  manual  page  describes the intermediate output format of the GNU
       roff(7) text processing system groff(1).  This output is produced by  a
       run  of  the GNU troff(1) program.  It contains already all device-spe-
       cific information, but it is not yet fed into  a  device  postprocessor
       program.

       As  the  GNU  roff processor groff(1) is a wrapper program around troff
       that automatically calls a postprocessor, this output does not show  up
       normally.   This is why it is called intermediate within the groff sys-
       tem.  The groff program provides the option -Z to inhibit  postprocess-
       ing,  such  that  the  produced intermediate output is sent to standard
       output just like calling troff manually.

       In this document, the term troff output describes what is output by the
       GNU  troff  program,  while  intermediate output refers to the language
       that is accepted by the parser that prepares this output for the  post-
       processors.   This parser is smarter on whitespace and implements obso-
       lete elements for compatibility, otherwise both formats are  the  same.
       Both formats can be viewed directly with gxditview(1).

       The  main  purpose  of the intermediate output concept is to facilitate
       the development of postprocessors by  providing  a  common  programming
       interface  for  all devices.  It has a language of its own that is com-
       pletely different from the groff(7) language.  While the groff language
       is  a high-level programming language for text processing, the interme-
       diate output language is a kind  of  low-level  assembler  language  by
       specifying all positions on the page for writing and drawing.

       The pre-groff roff versions are denoted as classical troff.  The inter-
       mediate output produced by groff is fairly  readable,  while  classical
       troff  output was hard to understand because of strange habits that are
       still supported, but not used any longer by GNU troff.

LANGUAGE CONCEPTS
       During the run of troff, the roff input is cracked down to the informa-
       tion on what has to be printed at what position on the intended device.
       So the language of the intermediate output format can be  quite  small.
       Its only elements are commands with or without arguments.  In this doc-
       ument, the term "command" always refers to the intermediate output lan-
       guage,  never to the roff language used for document formatting.  There
       are commands for positioning and text writing,  for  drawing,  and  for
       device controlling.

   Separation
       Classical  troff  output  had  strange requirements on whitespace.  The
       groff output parser, however, is smart about whitespace  by  making  it
       maximally  optional.   The whitespace characters, i.e., the tab, space,
       and newline characters, always have a syntactical  meaning.   They  are
       never  printable  because  spacing  within the output is always done by
       positioning commands.

       Any sequence of space or tab characters is treated as a single  syntac-
       tical space.  It separates commands and arguments, but is only required
       when there would occur a clashing between  the  command  code  and  the
       arguments  without  the  space.  Most often, this happens when variable
       length command names, arguments, argument lists,  or  command  clusters
       meet.   Commands  and  arguments with a known, fixed length need not be
       separated by syntactical space.

       A line break is a syntactical element, too.  Every command argument can
       be  followed  by whitespace, a comment, or a newline character.  Thus a
       syntactical line break is defined to consist  of  optional  syntactical
       space  that  is optionally followed by a comment, and a newline charac-
       ter.

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

       The  other commands -- those for drawing and device controlling -- have
       a more complicated structure; some recognize long  command  names,  and
       some take a variable number of arguments.  So all D and x commands were
       designed to request a syntactical line break after their last argument.
       Only  one  command, `x X' has an argument that can stretch over several
       lines, all other commands must have all of their arguments on the  same
       line  as the command, i.e., the arguments may not be splitted by a line
       break.

       Empty lines, i.e., lines containing only space and/or  a  comment,  can
       occur everywhere.  They are just ignored.

   Argument Units
       Some commands take integer arguments that are assumed to represent val-
       ues in a measurement unit, but the letter for the  corresponding  scale
       indicator  is  not  written  with  the  output  command  arguments; see
       groff(7) and the groff info file for more on this topic.  Most commands
       assume the scale indicator u, the basic unit of the device, some use z,
       the scaled point unit of the device, while others, such  as  the  color
       commands  expect  plain integers.  Note that these scale indicators are
       relative to the chosen device.  They  are  defined  by  the  parameters
       specified in the device's DESC file; see groff_font(5).

       Note  that  single  characters  can have the eighth bit set, as can the
       names of fonts and special characters.  The  names  of  characters  and
       fonts  can  be  of arbitrary length.  A character that is to be printed
       will always be in the current font.

       A string argument is always terminated by the next whitespace character
       (space,  tab,  or newline); an embedded # character is regarded as part
       of the argument, not as the beginning of a comment command.  An integer
       argument  is  already terminated by the next non-digit character, which
       then is regarded as the first character of the next  argument  or  com-
       mand.

   Document Parts
       A  correct intermediate output document consists of two parts, the pro-
       logue and the body.

       The task of the prologue is to set the general device parameters  using
       three  exactly specified commands.  The groff prologue is guaranteed to
       consist of the following three lines (in that order):

              x T device
              x res n h v
              x init

       with the arguments set as outlined in the section Device  Control  Com-
       mands.   But  the  parser for the intermediate output format is able to
       swallow additional whitespace and comments as well.

       The body is the main section for processing the document data.  Syntac-
       tically,  it is a sequence of any commands different from the ones used
       in the prologue.  Processing is terminated as soon as the first  x stop
       command  is encountered; the last line of any groff intermediate output
       always contains such a command.

       Semantically, the body is page oriented.  A new page is  started  by  a
       p  command.  Positioning, writing, and drawing commands are always done
       within the current page, so they cannot occur before the first  p  com-
       mand.   Absolute positioning (by the H and V commands) is done relative
       to the current page, all other positioning is done relative to the cur-
       rent location within this page.

COMMAND REFERENCE
       This  section describes all intermediate output commands, the classical
       commands as well as the groff extensions.

   Comment Command
       #anything<end_of_line>
              A comment.  Ignore any characters from the # character up to the
              next newline character.

       This command is the only possibility for commenting in the intermediate
       output.  Each comment can be preceded by arbitrary  syntactical  space;
       every command can be terminated by a comment.

   Simple Commands
       The  commands  in  this  subsection have a command code consisting of a
       single character, taking a fixed number of arguments.  Most of them are
       commands  for  positioning  and text writing.  These commands are smart
       about  whitespace.   Optionally,  syntactical  space  can  be  inserted
       before,  after,  and between the command letter and its arguments.  All
       of these commands are stackable, i.e., they can be  preceded  by  other
       simple  commands  or  followed  by arbitrary other commands on the same
       line.  A separating syntactical space is only necessary when two  inte-
       ger  arguments  would  clash  or  if the preceding argument ends with a
       string argument.

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

       c c    Print character c at the current print position; the character's
              size  is  read  from  the  font file.  The print position is not
              changed.

       f n    Set font to font number n (a non-negative integer).

       H n    Move right to the absolute vertical position n  (a  non-negative
              integer in basic units u) relative to left edge of current page.

       h n    Move n (a non-negative integer) basic units  u  horizontally  to
              the  right.   [CSTR  #54] allows negative values for n also, but
              groff doesn't use this.

       m color_scheme [component ...]
              Set the color for text (glyphs), line drawing, and  the  outline
              of graphic objects using different color schemes; the analoguous
              command for the filling color of graphic  objects  is  DF.   The
              color  components  are  specified as integer arguments between 0
              and 65536.  The number of color  components  and  their  meaning
              vary for the different color schemes.  These commands are gener-
              ated by the groff escape sequence  \m.   No  position  changing.
              These commands are a groff extension.

              mc cyan magenta yellow
                     Set  color using the CMY color scheme, having the 3 color
                     components cyan, magenta, and yellow.

              md     Set color to the  default  color  value  (black  in  most
                     cases).  No component arguments.

              mg gray
                     Set  color to the shade of gray given by the argument, an
                     integer between 0 (black) and 65536 (white).

              mk cyan magenta yellow black
                     Set color using the CMYK color scheme, having the 4 color
                     components cyan, magenta, yellow, and black.

              mr red green blue
                     Set  color using the RGB color scheme, having the 3 color
                     components red, green, and blue.

       N n    Print character with index n (an integer, normally non-negative)
              of  the  current  font.   The print position is not changed.  If
              -T html is used, negative values are emitted also to indicate an
              unbreakable  space with given width.  For example, N -193 repre-
              sents an unbreakable space which has a width of 193u.  This com-
              mand is a groff extension.

       n b a  Inform the device about a line break, but no positioning is done
              by this command.  In classical troff, the  integer  arguments  b
              and a informed about the space before and after the current line
              to make the intermediate output more human readable without per-
              forming  any  action.  In groff, they are just ignored, but they
              must be provided for compatibility reasons.

       p n    Begin a new page in the outprint.  The page number is set to  n.
              This  page is completely independent of pages formerly processed
              even if those have the same page number.  The vertical  position
              on  the  outprint  is  automatically set to 0.  All positioning,
              writing, and drawing is always done relative to  a  page,  so  a
              p command must be issued before any of these commands.

       s n    Set point size to n scaled points (this is unit z in GNU troff).
              Classical troff used the unit points (p)  instead;  see  section
              COMPATIBILITY.

       t xxx<white_space>
       t xxx dummy_arg<white_space>
              Print a word, i.e., a sequence of characters xxx terminated by a
              space character or a line  break;  an  optional  second  integer
              argument  is  ignored  (this allows the formatter to generate an
              even number  of  arguments).   The  first  character  should  be
              printed at the current position, the current horizontal position
              should then be increased by the width of  the  first  character,
              and  so on for each character.  The widths of the characters are
              read from the font file, scaled for the current point size,  and
              rounded  to  a  multiple  of the horizontal resolution.  Special
              characters cannot be printed using this command (use the C  com-
              mand  for named characters).  This command is a groff extension;
              it is only used for devices whose DESC file contains  the  tcom-
              mand keyword; see groff_font(5).

       u n xxx<white_space>
              Print  word  with track kerning.  This is the same as the t com-
              mand except that after printing each character, the current hor-
              izontal  position  is  increased by the sum of the width of that
              character and n (an integer in basic units u).  This command  is
              a  groff  extension; it is only used for devices whose DESC file
              contains the tcommand keyword; see groff_font(5).

       V n    Move down to the absolute vertical position  n  (a  non-negative
              integer  in  basic  units  u)  relative to upper edge of current
              page.

       v n    Move n basic  units  u  down  (n  is  a  non-negative  integer).
              [CSTR  #54] allows negative values for n also, but groff doesn't
              use this.

       w      Informs about a paddable  whitespace  to  increase  readability.
              The  spacing  itself must be performed explicitly by a move com-
              mand.

   Graphics Commands
       Each graphics or drawing command in the intermediate output starts with
       the  letter  D followed by one or two characters that specify a subcom-
       mand; this is followed by a fixed or variable number of  integer  argu-
       ments  that are separated by a single space character.  A D command may
       not be followed by another command on the same line (apart from a  com-
       ment), so each D command is terminated by a syntactical line break.

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

       Some  graphics  commands  can  take a variable number of arguments.  In
       this case, they are integers representing  a  size  measured  in  basic
       units  u.   The  arguments  called h1, h2, ..., hn stand for horizontal
       distances where positive means right,  negative  left.   The  arguments
       called  v1,  v2,  ...,  vn  stand for vertical distances where positive
       means down, negative up.  All these distances are offsets  relative  to
       the current location.

       Unless  indicated otherwise, each graphics command directly corresponds
       to a similar groff \D escape sequence; see groff(7).

       Unknown D commands are assumed to be  device-specific.   Its  arguments
       are  parsed as strings; the whole information is then sent to the post-
       processor.

       In the following command reference,  the  syntax  element  <line_break>
       means a syntactical line break as defined in section Separation.

       D~ h1 v1 h2 v2 ... hn vn<line_break>
              Draw  B-spline from current position to offset (h1, v1), then to
              offset (h2, v2) if given, etc.  up  to  (hn, vn).  This  command
              takes  a variable number of argument pairs; the current position
              is moved to the terminal point of the drawn curve.

       Da h1 v1 h2 v2<line_break>
              Draw arc from current position to (h1, v1)+(h2, v2) with  center
              at  (h1, v1);  then move the current position to the final point
              of the arc.

       DC d<line_break>
       DC d dummy_arg<line_break>
              Draw a solid circle using the current fill color with diameter d
              (integer  in  basic  units u) with leftmost point at the current
              position; then move the current position to the rightmost  point
              of  the  circle.  An optional second integer argument is ignored
              (this allows to the formatter to  generate  an  even  number  of
              arguments).  This command is a groff extension.

       Dc d<line_break>
              Draw circle line with diameter d (integer in basic units u) with
              leftmost point at the current position; then  move  the  current
              position to the rightmost point of the circle.

       DE h v<line_break>
              Draw a solid ellipse in the current fill color with a horizontal
              diameter of h and a vertical diameter of  v  (both  integers  in
              basic  units u) with the leftmost point at the current position;
              then move to the rightmost point of the ellipse.   This  command
              is a groff extension.

       De h v<line_break>
              Draw  an  outlined ellipse with a horizontal diameter of h and a
              vertical diameter of v (both integers in basic units u) with the
              leftmost  point  at current position; then move to the rightmost
              point of the ellipse.

       DF color_scheme [component ...]<line_break>
              Set fill color for solid drawing objects using  different  color
              schemes;  the  analoguous command for setting the color of text,
              line graphics, and the outline of graphic  objects  is  m.   The
              color  components  are  specified as integer arguments between 0
              and 65536.  The number of color  components  and  their  meaning
              vary for the different color schemes.  These commands are gener-
              ated by the groff escape sequences \D'F ...'  and  \M  (with  no
              other  corresponding  graphics commands).  No position changing.
              This command is a groff extension.

              DFc cyan magenta yellow<line_break>
                     Set fill color for solid drawing objects  using  the  CMY
                     color   scheme,  having  the  3  color  components  cyan,
                     magenta, and yellow.

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

              DFg gray<line_break>
                     Set fill color for solid drawing objects to the shade  of
                     gray  given by the argument, an integer between 0 (black)
                     and 65536 (white).

              DFk cyan magenta yellow black<line_break>
                     Set fill color for solid drawing objects using  the  CMYK
                     color   scheme,  having  the  4  color  components  cyan,
                     magenta, yellow, and black.

              DFr red green blue<line_break>
                     Set fill color for solid drawing objects  using  the  RGB
                     color  scheme,  having the 3 color components red, green,
                     and blue.

       Df n<line_break>
              The argument n must be an integer in the range -32767 to  32767.

              0 <= n <= 1000
                     Set  the  color  for  filling  solid drawing objects to a
                     shade of gray, where 0 corresponds to solid  white,  1000
                     (the  default)  to  solid black, and values in between to
                     intermediate shades of gray; this is obsoleted by command
                     DFg.

              n < 0 or n > 1000
                     Set  the  filling  color  to  the color that is currently
                     being used for the text and the outline, see  command  m.
                     For example, the command sequence
                            mg 0 0 65536
                            Df -1
                     sets all colors to blue.

              No position changing.  This command is a groff extension.

       Dl h v<line_break>
              Draw  line  from  current position to offset (h, v) (integers in
              basic units u); then set current position  to  the  end  of  the
              drawn line.

       Dp h1 v1 h2 v2 ... hn vn<line_break>
              Draw  a  polygon  line from current position to offset (h1, v1),
              from there to offset (h2, v2), etc. up to offset  (hn, vn),  and
              from  there  back to the starting position.  For historical rea-
              sons, the position is changed by adding the sum of all arguments
              with  odd  index  to the actual horizontal position and the even
              ones to the vertical position.  Although this doesn't make sense
              it  is  kept  for compatibility.  This command is a groff exten-
              sion.

       DP h1 v1 h2 v2 ... hn vn<line_break>
              The same macro as the corresponding Dp  command  with  the  same
              arguments,  but  draws a solid polygon in the current fill color
              rather than an outlined polygon.  The position is changed in the
              same way as with Dp.  This command is a groff extension.

       Dt n<line_break>
              Set  the  current  line  thickness  to  n  (an  integer in basic
              units u) if n>0; if  n=0  select  the  smallest  available  line
              thickness;  if  n<0  set  the line thickness proportional to the
              point size (this is the default before the first Dt command  was
              specified).   For historical reasons, the horizontal position is
              changed by adding the argument to the  actual  horizontal  posi-
              tion, while the vertical position is not changed.  Although this
              doesn't make sense it is kept for compatibility.   This  command
              is a groff extension.

   Device Control Commands
       Each  device  control  command  starts  with the letter x followed by a
       space character (optional or arbitrary space/tab in groff) and  a  sub-
       command  letter  or  word; each argument (if any) must be preceded by a
       syntactical space.  All x commands are terminated by a syntactical line
       break;  no device control command can be followed by another command on
       the same line (except a comment).

       The subcommand is basically a single letter, but to increase  readabil-
       ity,  it can be written as a word, i.e., an arbitrary sequence of char-
       acters terminated by the next tab, space, or  newline  character.   All
       characters  of  the  subcommand  word but the first are simply ignored.
       For example, troff outputs the initialization command x i as x init and
       the  resolution command x r as x res.  But writings like x i_like_groff
       and x roff_is_groff resp. are accepted as well to mean  the  same  com-
       mands.

       In  the  following, the syntax element <line_break> means a syntactical
       line break as defined in section Separation.

       xF name<line_break>
              (Filename control command)
              Use name as the intended name for  the  current  file  in  error
              reports.   This is useful for remembering the original file name
              when groff uses an internal piping mechanism.  The input file is
              not changed by this command.  This command is a groff extension.

       xf n s<line_break>
              (font control command)
              Mount font position n (a non-negative integer) with font named s
              (a text word), cf.  groff_font(5).

       xH n<line_break>
              (Height control command)
              Set  character  height  to  n  (a  positive  integer  in  scaled
              points z).  Classical troff used the unit  points  (p)  instead;
              see section COMPATIBILITY.

       xi<line_break>
              (init control command)
              Initialize device.  This is the third command of the prologue.

       xp<line_break>
              (pause control command)
              Parsed  but  ignored.   The  classical documentation reads pause
              device, can be restarted.

       xr n h v<line_break>
              (resolution control command)
              Resolution is n, while h is the minimal horizontal motion, and v
              the minimal vertical motion possible with this device; all argu-
              ments are positive integers in basic units u per inch.  This  is
              the second command of the prologue.

       xS n<line_break>
              (Slant control command)
              Set slant to n degrees (an integer in basic units u).

       xs<line_break>
              (stop control command)
              Terminates  the  processing  of  the current file; issued as the
              last command of any intermediate troff output.

       xt<line_break>
              (trailer control command)
              Generate trailer information, if any.  In groff, this  is  actu-
              ally just ignored.

       xT xxx<line_break>
              (Typesetter control command)
              Set  name  of device to word xxx, a sequence of characters ended
              by the next whitespace character.   The  possible  device  names
              coincide with those from the groff -T option.  This is the first
              command of the prologue.

       xu n<line_break>
              (underline control command)
              Configure underlining of spaces.  If n is 1,  start  underlining
              of  spaces;  if  n  is  0,  stop underlining of spaces.  This is
              needed for the cu request in nroff mode and  is  ignored  other-
              wise.  This command is a groff extension.

       xX anything<line_break>
              (X-escape control command)
              Send  string  anything uninterpreted to the device.  If the line
              following this command starts with a + character  this  line  is
              interpreted  as a continuation line in the following sense.  The
              + is ignored, but a newline character is  sent  instead  to  the
              device,  the  rest  of the line is sent uninterpreted.  The same
              applies to all following lines until the first  character  of  a
              line  is  not  a  + character.  This command is generated by the
              groff escape sequence \X.   The  line-continuing  feature  is  a
              groff extension.

   Obsolete Command
       In classical troff output, the writing of a single character was mostly
       done by a very strange command that combined a horizontal move and  the
       printing  of a character.  It didn't have a command code, but is repre-
       sented by a 3-character argument consisting of exactly 2 digits  and  a
       character.

       ddc    Move  right  dd (exactly two decimal digits) basic units u, then
              print character c.

              In groff, arbitrary syntactical space  around  and  within  this
              command  is  allowed to be added.  Only when a preceding command
              on the same line ends with an argument of variable length a sep-
              arating space is obligatory.  In classical troff, large clusters
              of these and other commands were used,  mostly  without  spaces;
              this made such output almost unreadable.

       For  modern  high-resolution  devices, this command does not make sense
       because the width of the characters can become  much  larger  than  two
       decimal  digits.   In  groff,  this  is  only used for the devices X75,
       X75-12, X100, and X100-12.  For other devices, the  commands  t  and  u
       provide a better functionality.

POSTPROCESSING
       The  roff  postprocessors  are programs that have the task to translate
       the intermediate output into actions that are  sent  to  a  device.   A
       device  can  be some piece of hardware such as a printer, or a software
       file format suitable for graphical or text processing.  The groff  sys-
       tem  provides powerful means that make the programming of such postpro-
       cessors an easy task.

       There is a library function that parses  the  intermediate  output  and
       sends  the  information  obtained  to the device via methods of a class
       with a common interface for each device.  So a groff postprocessor must
       only  redefine  the methods of this class.  For details, see the refer-
       ence in section FILES.

EXAMPLES
       This section presents the intermediate output generated from  the  same
       input  for  three  different  devices.   The input is the sentence hell
       world fed into groff on the command line.

       o High-resolution device ps

         shell> echo hell world | groff -Z -T ps

         x T ps
         x res 72000 1 1
         x init
         p1
         x font 5 TR
         f5
         s10000
         V12000
         H72000
         thell
         wh2500
         tw
         H96620
         torld
         n12000 0
         x trailer
         V792000
         x stop

       This output can be fed into the postprocessor grops(1) to get its  rep-
       resentation as a PostScript file.

       o Low-resolution device latin1

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

         shell> echo hell world | groff -Z -T latin1

         # prologue
         x T latin1
         x res 240 24 40
         x init
         # begin a new page
         p1
         # font setup
         x font 1 R
         f1
         s10
         # initial positioning on the page
         V40
         H0
         # write text `hell'
         thell
         # inform about a space, and do it by a horizontal jump
         wh24
         # write text `world'
         tworld
         # announce line break, but do nothing because ...
         n40 0
         # ... the end of the document has been reached
         x trailer
         V2640
         x stop

       This output can be fed into the postprocessor grotty(1) to get  a  for-
       matted text document.

       o Classical style output

         As  a  computer  monitor has a very low resolution compared to modern
         printers the intermediate output for the X devices can use the  jump-
         and-write command with its 2-digit displacements.

         shell> echo hell world | groff -Z -T X100

         x T X100
         x res 100 1 1
         x init
         p1
         x font 5 TR
         f5
         s10
         V16
         H100
         # write text with old-style jump-and-write command
         ch07e07l03lw06w11o07r05l03dh7
         n16 0
         x trailer
         V1100
         x stop

       This   output  can  be  fed  into  the  postprocessor  xditview(1x)  or
       gxditview(1) for displaying in X.

       Due to the obsolete jump-and-write command, the text  clusters  in  the
       classical output are almost unreadable.

COMPATIBILITY
       The intermediate output language of the classical troff was first docu-
       mented in [CSTR #97].  The groff intermediate output format is compati-
       ble with this specification except for the following features.

       o The classical quasi device independence is not yet implemented.

       o The  old  hardware was very different from what we use today.  So the
         groff devices are also fundamentally different from the ones in clas-
         sical troff.  For example, the classical PostScript device was called
         post and had a resolution of 720 units per  inch,  while  groff's  ps
         device  has  a  resolution of 72000 units per inch.  Maybe, by imple-
         menting some rescaling  mechanism  similar  to  the  classical  quasi
         device independence, these could be integrated into modern groff.

       o The B-spline command D~ is correctly handled by the intermediate out-
         put parser, but the drawing routines aren't implemented  in  some  of
         the postprocessor programs.

       o The  argument  of the commands s and x H has the implicit unit scaled
         point z in groff, while classical troff had point (p).  This isn't an
         incompatibility,  but a compatible extension, for both units coincide
         for all devices without a sizescale parameter, including all  classi-
         cal  and  the  groff  text  devices.   The  few  groff devices with a
         sizescale parameter either did not exist, had a  different  name,  or
         seem to have had a different resolution.  So conflicts with classical
         devices are very unlikely.

       o The position changing after the commands Dp, DP, and Dt is illogical,
         but as old versions of groff used this feature it is kept for compat-
         ibility reasons.

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

FILES
       /usr/share/groff_font/devname/DESC
              Device description file for device name.

       <groff_source_dir>/src/libs/libdriver/input.cpp
              Defines  the  parser and postprocessor for the intermediate out-
              put.  It is located relative to the top directory of  the  groff
              source tree, e.g.  @GROFFSRCDIR@.  This parser is the definitive
              specification of the groff intermediate output format.

SEE ALSO
       A reference like groff(7) refers to a manual page; here groff  in  sec-
       tion 7 of the man-page documentation system.  To read the example, look
       up section 7 in your desktop help system or call from the shell prompt

              shell> man 7 groff

       For more details, see man(1).

       groff(1)
              option -Z and further readings on groff.

       groff(7)
              for details of the groff language such as  numerical  units  and
              escape sequences.

       groff_font(5)
              for details on the device scaling parameters of the DESC file.

       troff(1)
              generates the device-independent intermediate output.

       roff(7)
              for  historical  aspects  and the general structure of roff sys-
              tems.

       groff_diff(7)
              The differences between the intermediate  output  in  groff  and
              classical troff.

       gxditview(1)
              Viewer for the intermediate output.

       grodvi(1), grohtml(1), grolbp(1), grolj4(1), grops(1), grotty(1)
              the groff postprocessor programs.

       For a treatment of all aspects of the groff system within a single doc-
       ument, see the groff info file.  It can be read within  the  integrated
       help systems, within emacs(1) or from the shell prompt by
              shell> info groff

       The  classical troff output language is described in two AT&T Bell Labs
       CSTR documents available on-line at Bell Labs CSTR site <http://
       cm.bell-labs.com/cm/cs/cstr.html>.

       [CSTR #97]
              A  Typesetter-independent TROFF by Brian Kernighan is the origi-
              nal and most concise documentation on the output language; see
              CSTR #97 <http://cm.bell-labs.com/cm/cs/cstr/97.ps.gz>.

       [CSTR #54]
              The  1992  revision  of  the  Nroff/Troff User's Manual by J. F.
              Osanna and Brian  Kernighan  isn't  as  concise  as  [CSTR  #97]
              regarding the output language; see CSTR #54 <http://
              cm.bell-labs.com/cm/cs/cstr/54.ps.gz>.

AUTHORS
       Copyright (C) 1989, 2001, 2002, 2003, 2004  Free  Software  Foundation,
       Inc.

       This document is distributed under the terms of the FDL (GNU Free Docu-
       mentation License) version 1.1 or later.  You should  have  received  a
       copy of the FDL with this package; it is also available on-line at the
       GNU copyleft site <http://www.gnu.org/copyleft/fdl.html>.

       This document is part of groff, the GNU roff distribution.  It is based
       on  a  former  version  - published under the GPL - that described only
       parts of the groff extensions of the  output  language.   It  has  been
       rewritten  2002  by  Bernd  Warken  and is maintained by Werner Lemberg
       <wl@gnu.org>.



Groff Version 1.19.2            6 February 2006                   GROFF_OUT(5)

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