groff_out

GROFF_OUT(5)                   File Formats Manual                  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-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 stacking of 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 Groff: The GNU Implementation of troff, the groff Texinfo manual, 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 subsection “Device Control
       Commands” below.  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 analogous
              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” below.

       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 subsection “Separation” above.

       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 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 analogous 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 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 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 subsection “Separation” above.

       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); see 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” below.

       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” below.

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, or gropdf(1) to output directly to
       PDF.

       • 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.

       • 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.

       • 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/1.22.4/font/devname/DESC
              Device description file for device name.

       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.

AUTHORS
       James Clark wrote an early version of this document, which described only
       the differences between ditroff(7)'s output format and that of GNU roff.
       The present version was completely rewritten in 2001 by Bernd Warken
       ⟨groff-bernd.warken-72@web.de⟩.

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.

       Groff: The GNU Implementation of troff, by Trent A. Fisher and Werner
       Lemberg, is the primary groff manual.  You can browse it interactively
       with “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⟩.



groff 1.22.4                      21 June 2021                      GROFF_OUT(5)