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groff_out(5)               File Formats Manual              groff_out(5)

Name         top

       groff_out - GNU roff intermediate output format

Description         top

       The fundamental operation of the troff(1) formatter is the
       translation of the groff(7) input language into a device-
       independent form, described here, primarily concerned with what
       has to be written or drawn at specific positions on the output
       device.  This language is simple and imperative.  In the
       following discussion, the term command always refers to this
       intermediate output language, and never to the groff(7) language
       intended for direct use by document authors.  Intermediate output
       commands comprise several categories: glyph output; font, color,
       and text size selection; motion of the printing position; page
       advancement; drawing of geometric primitives; and device control
       commands, a catch-all for operations not easily classified as any
       of the foregoing, such as directives to start and stop output,
       identify the intended output device, or place URL hyperlinks in
       supported output formats.

       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         top

       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 scaling 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 scaling 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 scaling 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         top

       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      Describe an adjustable space.  This performs no action; it
              is present for documentary purposes.  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 the name of the output driver to xxx, a sequence of
              non-whitespace characters terminated by whitespace.  The
              possible names correspond to those of groff's -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         top

       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.

Example         top

       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         top

       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         top

       /usr/local/share/groff/1.23.0/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         top

       James Clark wrote an early version of this document, which
       described only the differences between AT&T device-independent
       troff'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         top

       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”.

       “Troff User's Manual” by Joseph F. Ossanna, 1976 (revised by
       Brian W. Kernighan, 1992), AT&T Bell Laboratories Computing
       Science Techical Report No. 54, widely called simply “CSTR #54”,
       documents the language, device and font description file formats,
       and device-independent output format referred to collectively in
       groff documentation as “AT&T troff”.

       “A Typesetter-independent TROFF” by Brian W. Kernighan, 1982,
       AT&T Bell Laboratories Computing Science Techical Report No. 97,
       provides additional insights into the device and font description
       file formats and device-independent output format.

       groff(1)
              documents the -Z option and contains pointers to further
              groff documentation.

       groff(7)
              describes the groff language, including its escape
              sequences and system of units.

       groff_font(5)
              details the device scaling parameters of device DESC
              files.

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

       roff(7)
              presents historical aspects and the general structure of
              roff systems.

       groff_diff(7)
              enumerates differences between the intermediate output
              produced by AT&T troff and that of groff.

       gxditview(1)
              is a viewer for intermediate output.

       grodvi(1), grohtml(1), grolbp(1), grolj4(1), gropdf(1), grops(1),
       and grotty(1) are groff postprocessors.

COLOPHON         top

       This page is part of the groff (GNU troff) project.  Information
       about the project can be found at 
       ⟨http://www.gnu.org/software/groff/⟩.  If you have a bug report
       for this manual page, see ⟨http://www.gnu.org/software/groff/⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2021-08-27.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-08-23.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

groff 1.23.0.rc1.654-4e1db-dir1t9yAugust 2021                 groff_out(5)

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