Provided by: groff_1.22.4-8build1_amd64 bug

NAME

       groff_diff - differences between GNU troff and classical troff

DESCRIPTION

       This  manual  page describes the language differences between groff, the GNU roff text processing system,
       and the classical roff formatter of the freely available Unix 7 of the 1970s,  documented  in  the  Troff
       User's  Manual  by  Ossanna  and  Kernighan.  This includes the roff language as well as the intermediate
       output format (troff output).

       Section “See Also” below gives pointers to both the classical roff and the modern groff documentation.

GROFF LANGUAGE

       In this section, all additional features of groff compared to the classical Unix 7 troff are described in
       detail.

   Long names
       The names of number registers, fonts, strings/macros/diversions, special characters (glyphs), and  colors
       can  be  of any length.  In escape sequences, additionally to the classical ‘(xx’ construction for a two-
       character glyph name, you can use ‘[xxx]’ for a name of arbitrary length.

       \[xxx] Print the special character (glyph) called xxx.

       \[comp1 comp2 ...]
              Print composite glyph consisting of multiple components.  Example: ‘\[A ho]’ is capital  letter  A
              with  ogonek  which finally maps to glyph name ‘u0041_0328’.  See Groff: The GNU Implementation of
              troff, the groff Texinfo manual, for details of  how  a  glyph  name  for  a  composite  glyph  is
              constructed, and groff_char(7) for a list of glyph name components used in composite glyph names.

       \f[xxx]
              Set  font  xxx.   Additionally,  \f[]  is  a  new syntax form equal to \fP, i.e., to return to the
              previous font.

       \*[xxx arg1 arg2 ...]
              Interpolate string xxx, taking arg1, arg2, ..., as arguments.

       \n[xxx]
              Interpolate number register xxx.

   Fractional point sizes
       A scaled point is equal to 1/sizescale points, where sizescale is  specified  in  the  DESC  file  (1  by
       default).   There  is  a new scale indicator z that has the effect of multiplying by sizescale.  Requests
       and escape sequences in troff interpret arguments that represent a point size as being in units of scaled
       points, but they evaluate each such argument using a default scale indicator of z.  Arguments treated  in
       this  way are the argument to the ps request, the third argument to the cs request, the second and fourth
       arguments to the tkf request, the argument to the \H escape sequence, and those variants of the \s escape
       sequence that take a numeric expression as their argument.

       For example, suppose sizescale is 1000; then a scaled point is  equivalent  to  a  millipoint;  the  call
       .ps 10.25  is  equivalent to .ps 10.25z and so sets the point size to 10250 scaled points, which is equal
       to 10.25 points.

       The number register \n[.s] returns the point size in points as decimal fraction.  There  is  also  a  new
       number register \n[.ps] that returns the point size in scaled points.

       It would make no sense to use the z scale indicator in a numeric expression whose default scale indicator
       was  neither  u  nor  z,  and so troff disallows this.  Similarly it would make no sense to use a scaling
       indicator other than z or u in a numeric expression whose default scale indicator was  z,  and  so  troff
       disallows this as well.

       There  is  also new scale indicator s which multiplies by the number of units in a scaled point.  So, for
       example, \n[.ps]s is equal to 1m.  Be sure not to confuse the s and z scale indicators.

   Numeric expressions
       Spaces are permitted in a number expression within parentheses.

       M indicates a scale of 100ths of an em.  f indicates a scale of  65536  units,  providing  fractions  for
       color definitions with the defcolor request.  For example, 0.5f = 32768u.

       e1>?e2 The maximum of e1 and e2.

       e1<?e2 The minimum of e1 and e2.

       (c;e)  Evaluate  e  using c as the default scaling indicator.  If c is missing, ignore scaling indicators
              in the evaluation of e.

   New escape sequences
       \A'anything'
              This expands to 1 or 0, depending on whether anything is or is not acceptable as  the  name  of  a
              string,  macro, diversion, number register, environment, font, or color.  It returns 0 if anything
              is empty.  This is useful if you want to look up user input in some sort of associative table.

       \B'anything'
              This expands to 1 or 0, depending on whether anything is or is not a valid numeric expression.  It
              returns 0 if anything is empty.

       \C'xxx'
              Typeset glyph named xxx.  Normally it is more convenient to use \[xxx].  But \C has the  advantage
              that it is compatible with recent versions of Unix and is available in compatibility mode.

       \E     This  is  equivalent to an escape character, but it is not interpreted in copy mode.  For example,
              strings to start and end superscripting could be defined like this

                     .ds { \v'-.3m'\s'\En[.s]*6u/10u'
                     .ds } \s0\v'.3m'

              The use of \E ensures that these definitions work even if \*{ gets interpreted in copy  mode  (for
              example, by being used in a macro argument).

       \Ff
       \F(fm
       \F[fam]
              Change font family.  This is the same as the fam request.  \F[] switches back to the previous font
              family (note that \FP won't work; it selects font family ‘P’ instead).

       \mx
       \m(xx
       \m[xxx]
              Set drawing color.  \m[] switches back to the previous color.

       \Mx
       \M(xx
       \M[xxx]
              Set  background  color  for filled objects drawn with the \D'...' commands.  \M[] switches back to
              the previous color.

       \N'n'  Typeset the glyph with index n in the current font.  n can be any integer.  Most devices only have
              glyphs with indices between 0 and 255.  If the current font does not contain  a  glyph  with  that
              code,  special  fonts  are  not  searched.   The  \N  escape  sequence can be conveniently used in
              conjunction with the char request, for example

                     .char \[phone] \f(ZD\N'37'

              The index of each glyph is given in the fourth column in  the  font  description  file  after  the
              charset command.  It is possible to include unnamed glyphs in the font description file by using a
              name of ---; the \N escape sequence is the only way to use these.

       \On
       \O[n]  Suppress  troff  output.   The  escapes  \O2,  \O3,  \O4, and \O5 are intended for internal use by
              grohtml.

              \O0    Disable any ditroff glyphs from being emitted to  the  device  driver,  provided  that  the
                     escape occurs at the outer level (see \O3 and \O4).

              \O1    Enable output of glyphs, provided that the escape occurs at the outer level.

                     \O0  and  \O1  also  reset the registers \n[opminx], \n[opminy], \n[opmaxx], and \n[opmaxy]
                     to -1.  These four registers mark the top left and bottom right hand corners of a box which
                     encompasses all written glyphs.

              \O2    Provided that the escape occurs at the outer level, enable output of glyphs and also  write
                     out to stderr the page number and four registers encompassing the glyphs previously written
                     since the last call to \O.

              \O3    Begin  a  nesting level.  At start-up, troff is at outer level.  This is really an internal
                     mechanism for grohtml while producing images.  They are  generated  by  running  the  troff
                     source  through  troff  to  the  PostScript device and ghostscript to produce images in PNG
                     format.  The \O3 escape starts a new page  if  the  device  is  not  html  (to  reduce  the
                     possibility of images crossing a page boundary).

              \O4    End a nesting level.

              \O5[Pfilename]
                     This  escape  is  grohtml  specific.  Provided that this escape occurs at the outer nesting
                     level, write filename to stderr.  The position of the image, P, must be specified and  must
                     be  one  of l, r, c, or i (left, right, centered, inline).  filename is associated with the
                     production of the next inline image.

       \R'name ±n'
              This has the same effect as

                     .nr name ±n

       \s(nn
       \s±(nn Set the point size to nn points; nn must be exactly two digits.

       \s[±n]
       \s±[n]
       \s'±n'
       \s±'n' Set the point size to n scaled points; n is a numeric expression with a  default  scale  indicator
              of z.

       \Vx
       \V(xx
       \V[xxx]
              Interpolate  the  contents  of  the  environment  variable  xxx,  as returned by getenv(3).  \V is
              interpreted in copy mode.

       \Yx
       \Y(xx
       \Y[xxx]
              This is approximately equivalent to \X'\*[xxx]'.  However the contents of the string or macro  xxx
              are not interpreted; also it is permitted for xxx to have been defined as a macro and thus contain
              newlines  (it  is  not  permitted  for  the argument to \X to contain newlines).  The inclusion of
              newlines requires an extension to the Unix troff output format, and confuses drivers that  do  not
              know about this extension.

       \Z'anything'
              Print  anything  and  then  restore the horizontal and vertical position; anything may not contain
              tabs or leaders.

       \$0    The name by which the current macro was invoked.  The als request can make a macro have more  than
              one name.

       \$*    In a macro or string, the concatenation of all the arguments separated by spaces.

       \$@    In  a  macro  or  string,  the  concatenation  of all the arguments with each surrounded by double
              quotes, and separated by spaces.

       \$^    In a macro, the representation of all parameters as if they were an argument to the ds request.

       \$(nn
       \$[nnn]
              In a macro or string, this gives the nn-th or nnn-th argument.  Macros and  strings  can  have  an
              unlimited number of arguments.

       \?anything\?
              When  used  in a diversion, this transparently embeds anything in the diversion.  anything is read
              in copy mode.  When the diversion is reread, anything is interpreted.  anything  may  not  contain
              newlines;  use  \!  if  you want to embed newlines in a diversion.  The escape sequence \? is also
              recognized in copy mode and turned into a single internal code; it is this  code  that  terminates
              anything.  Thus

                     .nr x 1
                     .nf
                     .di d
                     \?\\?\\\\?\\\\\\\\nx\\\\?\\?\?
                     .di
                     .nr x 2
                     .di e
                     .d
                     .di
                     .nr x 3
                     .di f
                     .e
                     .di
                     .nr x 4
                     .f

              prints 4.

       \/     This  increases  the  width  of the preceding glyph so that the spacing between that glyph and the
              following glyph is correct if the following glyph is a roman glyph.  It is a good idea to use this
              escape sequence whenever an italic glyph is immediately followed by  a  roman  glyph  without  any
              intervening space.

       \,     This  modifies  the  spacing of the following glyph so that the spacing between that glyph and the
              preceding glyph is correct if the preceding glyph is a roman glyph.  It is a good idea to use this
              escape sequence whenever a roman glyph is immediately followed by  an  italic  glyph  without  any
              intervening space.

       \)     Like \& except that it behaves like a character declared with the cflags request to be transparent
              for the purposes of end-of-sentence recognition.

       \~     This  produces  an  unbreakable space that stretches like a normal inter-word space when a line is
              adjusted.

       \:     This causes the insertion of a zero-width break point.  It is  equal  to  \%  within  a  word  but
              without insertion of a soft hyphen glyph.

       \#     Everything up to and including the next newline is ignored.  This is interpreted in copy mode.  It
              is like \" except that \" does not ignore the terminating newline.

   New requests
       .aln xx yy
              Create an alias xx for number register object named yy.  The new name and the old name are exactly
              equivalent.  If yy is undefined, a warning of type reg is generated, and the request is ignored.

       .als xx yy
              Create an alias xx for request, string, macro, or diversion object named yy.  The new name and the
              old  name  are  exactly  equivalent  (it  is similar to a hard rather than a soft link).  If yy is
              undefined, a warning of type mac is generated, and the request is ignored.  The de,  am,  di,  da,
              ds,  and  as  requests  only  create a new object if the name of the macro, diversion or string is
              currently undefined or if it is defined to be a request; normally they  modify  the  value  of  an
              existing object.

       .am1 xx yy
              Similar  to  .am,  but compatibility mode is switched off during execution.  To be more precise, a
              ‘compatibility  save’  token  is  inserted  at  the  beginning  of  the  macro  addition,  and   a
              ‘compatibility restore’ token at the end.  As a consequence, the requests am, am1, de, and de1 can
              be  intermixed  freely  since  the  compatibility  save/restore tokens only affect the macro parts
              defined by .am1 and .ds1.

       .ami xx yy
              Append to macro indirectly.  See the dei request below for more information.

       .ami1 xx yy
              Same as the ami request but compatibility mode is switched off during execution.

       .as1 xx yy
              Similar to .as, but compatibility mode is switched off during expansion.  To be  more  precise,  a
              ‘compatibility  save’  token  is  inserted  at  the  beginning of the string, and a ‘compatibility
              restore’ token at the end.  As a consequence, the requests as, as1, ds, and ds1 can be  intermixed
              freely since the compatibility save/restore tokens only affect the (sub)strings defined by as1 and
              ds1.

       .asciify xx
              This  request ‘unformats’ the diversion xx in such a way that ASCII and space characters (and some
              escape sequences) that were formatted and  diverted  into  xx  are  treated  like  ordinary  input
              characters  when  xx is reread.  Useful for diversions in conjunction with the writem request.  It
              can be also used for gross hacks; for example, this

                     .tr @.
                     .di x
                     @nr n 1
                     .br
                     .di
                     .tr @@
                     .asciify x
                     .x

              sets register n to 1.  Note that glyph information (font, font size, etc.) is not  preserved;  use
              .unformat instead.

       .backtrace
              Print a backtrace of the input stack on stderr.

       .blm xx
              Set  the  blank line macro to xx.  If there is a blank line macro, it is invoked when a blank line
              is encountered instead of the usual troff behaviour.

       .box xx
       .boxa xx
              These requests are similar to the di and da requests with the exception that  a  partially  filled
              line does not become part of the diversion (i.e., the diversion always starts with a new line) but
              is  restored after ending the diversion, discarding the partially filled line which possibly comes
              from the diversion.

       .break Break out of a while loop.  See also the while and continue requests.  Be sure not to confuse this
              with the br request.

       .brp   This is the same as \p.

       .cflags n c1 c2 ...
              Characters c1, c2, ..., have properties determined by n, which is ORed from the following:

              1      The character ends sentences (initially characters .?! have this property).

              2      Lines can be broken before the character (initially no characters have  this  property);  a
                     line  is  not  broken  at a character with this property unless the characters on each side
                     both have non-zero hyphenation codes.  This can be overridden with value 64.

              4      Lines can be broken  after  the  character  (initially  characters  -\[hy]\[em]  have  this
                     property);  a line is not broken at a character with this property unless the characters on
                     each side both have non-zero hyphenation codes.  This can be overridden with value 64.

              8      The glyph associated  with  this  character  overlaps  horizontally  (initially  characters
                     \[ul]\[rn]\[ru]\[radicalex]\[sqrtex] have this property).

              16     The  glyph  associated  with  this character overlaps vertically (initially glyph \[br] has
                     this property).

              32     An end-of-sentence character followed by any number of characters  with  this  property  is
                     treated as the end of a sentence if followed by a newline or two spaces; in other words the
                     character  is transparent for the purposes of end-of-sentence recognition; this is the same
                     as having a zero space factor in TeX (initially characters "')]*\[dg]\[rq]\[cq]  have  this
                     property).

              64     Ignore hyphenation code values of the surrounding characters.  Use this in combination with
                     values 2 and 4 (initially no characters have this property).

              128    Prohibit  a  line  break  before the character, but allow a line break after the character.
                     This works only in combination with flags 256 and 512 and has no effect otherwise.

              256    Prohibit a line break after the character, but allow a line  break  before  the  character.
                     This works only in combination with flags 128 and 512 and has no effect otherwise.

              512    Allow  line break before or after the character.  This works only in combination with flags
                     128 and 256 and has no effect otherwise.

              Contrary to flag values 2 and 4, the flags 128, 256, and 512 work pairwise.  If, for example,  the
              left character has value 512, and the right character 128, no line break gets inserted.  If we use
              value 6 instead for the left character, a line break after the character can't be suppressed since
              the right neighbour character doesn't get examined.

       .char c string
              [This request can both define characters and glyphs.]

              Define  entity c to be string.  To be more precise, define (or even override) a groff entity which
              can be accessed with name c on the input side, and which uses string on the  output  side.   Every
              time glyph c needs to be printed, string is processed in a temporary environment and the result is
              wrapped up into a single object.  Compatibility mode is turned off and the escape character is set
              to  \  while  string  is  being  processed.  Any emboldening, constant spacing or track kerning is
              applied to this object rather than to individual glyphs in string.

              A groff object defined by this request can be used just like a normal glyph provided by the output
              device.  In particular other characters can be translated to it with the tr  request;  it  can  be
              made  the  leader glyph by the lc request; repeated patterns can be drawn with the glyph using the
              \l and \L escape sequences; words containing c can be hyphenated correctly, if the  hcode  request
              is used to give the object a hyphenation code.

              There  is  a special anti-recursion feature: Use of glyph within the glyph's definition is handled
              like normal glyphs not defined with char.

              A glyph definition can be removed with the rchar request.

       .chop xx
              Chop the last element off macro, string, or diversion xx.  This is useful for removing the newline
              from the end of diversions that are to be interpolated as strings.

       .class name c1 c2 ...
              Assign name to a set of characters c1, c2, ..., so  that  they  can  be  referred  to  from  other
              requests easily (currently .cflags only).  Character ranges (indicated by an intermediate ‘-’) and
              nested  classes  are  possible  also.   This  is  useful  to  assign  properties to a large set of
              characters.

       .close stream
              Close the stream named stream; stream will no longer  be  an  acceptable  argument  to  the  write
              request.  See the open request.

       .composite glyph1 glyph2
              Map glyph name glyph1 to glyph name glyph2 if it is used in \[...] with more than one component.

       .continue
              Finish the current iteration of a while loop.  See also the while and break requests.

       .color n
              If n is non-zero or missing, enable colors (this is the default), otherwise disable them.

       .cp n  If  n  is  non-zero or missing, enable compatibility mode, otherwise disable it.  In compatibility
              mode, long names are not recognized, and the incompatibilities caused by long names do not arise.

       .defcolor xxx scheme color_components
              Define color xxx.  scheme can be one of the following values: rgb (three components),  cmy  (three
              components),  cmyk  (four  components), and gray or grey (one component).  Color components can be
              given either as a hexadecimal string or as positive decimal integers  in  the  range  0–65535.   A
              hexadecimal  string contains all color components concatenated; it must start with either # or ##.
              The former specifies hex values in the range 0–255 (which are internally multiplied by  257),  the
              latter  in  the range 0–65535.  Examples: #FFC0CB (pink), ##ffff0000ffff (magenta).  A new scaling
              indicator f has been introduced which multiplies its value by 65536; this makes it  convenient  to
              specify color components as fractions in the range 0 to 1.  Example:

                     .defcolor darkgreen rgb 0.1f 0.5f 0.2f

              Note that f is the default scaling indicator for the defcolor request, thus the above statement is
              equivalent to

                     .defcolor darkgreen rgb 0.1 0.5 0.2

              The  color  named  default (which is device-specific) can't be redefined.  It is possible that the
              default color for \M and \m is not the same.

       .de1 xx yy
              Similar to .de, but compatibility mode is switched off during execution.  On  entry,  the  current
              compatibility mode is saved and restored at exit.

       .dei xx yy
              Define macro indirectly.  The following example

                     .ds xx aa
                     .ds yy bb
                     .dei xx yy

              is equivalent to

                     .de aa bb

       .dei1 xx yy
              Similar to the dei request but compatibility mode is switched off during execution.

       .device anything
              This  is  (almost)  the  same  as  the  \X  escape.  anything is read in copy mode; a leading " is
              stripped.

       .devicem xx
              This is the same as the \Y escape (to embed the contents of a macro into the  intermediate  output
              preceded with ‘x X’).

       .do xxx
              Interpret .xxx with compatibility mode disabled.  For example,

                     .do fam T

              would have the same effect as

                     .fam T

              except  that  it  would  work even if compatibility mode had been enabled.  Note that the previous
              compatibility mode is restored before any files sourced by xxx are interpreted.

       .ds1 xx yy
              Similar to .ds, but compatibility mode is switched off during expansion.  To be  more  precise,  a
              ‘compatibility  save’  token  is  inserted  at  the  beginning of the string, and a ‘compatibility
              restore’ token at the end.

       .ecs   Save current escape character.

       .ecr   Restore escape character saved with ecs.  Without a previous call to ecs,  ‘\’  will  be  the  new
              escape character.

       .evc xx
              Copy  the  contents  of  environment  xx  to  the  current  environment.  No pushing or popping of
              environments is done.

       .fam xx
              Set the current font family to xx.  The current font family is part of  the  current  environment.
              If  xx  is  missing,  switch back to previous font family.  The value at start-up is ‘T’.  See the
              description of the sty request for more information on font families.

       .fchar c string
              Define fallback character (or glyph) c to be string.  The syntax of this request is  the  same  as
              the  char  request; the only difference is that a glyph defined with char hides the glyph with the
              same name in the current font, whereas  a  glyph  defined  with  fchar  is  checked  only  if  the
              particular  glyph  isn't  found  in  the  current font.  This test happens before checking special
              fonts.

       .fcolor c
              Set the fill color to c.  If c is missing, switch to the previous fill color.

       .fschar f c string
              Define fallback character (or glyph) c for font f to be string.  The syntax of this request is the
              same as the char request (with an additional argument to specify the font); a glyph  defined  with
              fschar  is searched after the list of fonts declared with the fspecial request but before the list
              of fonts declared with .special.

       .fspecial f s1 s2 ...
              When the current font is f, fonts s1, s2, ..., are special, that is, they are searched for  glyphs
              not  in  the  current  font.   Any fonts specified in the special request are searched after fonts
              specified in the fspecial request.  Without argument, reset the list of global special fonts to be
              empty.

       .ftr f g
              Translate font f to g.  Whenever a font named f is referred to in an \f escape sequence, in the  F
              and  S  conditional  operators,  or  in  the  ft,  ul,  bd, cs, tkf, special, fspecial, fp, or sty
              requests, font g is used.  If g is missing, or equal to f then font f is not translated.

       .fzoom f zoom
              Set zoom factor zoom for font f.  zoom must a non-negative integer multiple of 1/1000th.  If it is
              missing or is equal to zero, it means the same as 1000, namely no magnification.  f must be a real
              font name, not a style.

       .gcolor c
              Set the glyph color to c.  If c is missing, switch to the previous glyph color.

       .hcode c1 code1 c2 code2 ...
              Set the hyphenation code of character c1 to code1  and  that  of  c2  to  code2,  and  so  on.   A
              hyphenation  code must be a single input character (not a special character) other than a digit or
              a space.  Initially each lower-case letter a–z has a hyphenation code, which is itself,  and  each
              upper-case  letter A–Z has a hyphenation code which is the lower-case version of itself.  See also
              the hpf request.

       .hla lang
              Set the current hyphenation language to  lang.   Hyphenation  exceptions  specified  with  the  hw
              request  and  hyphenation  patterns  specified  with  the hpf request are both associated with the
              current hyphenation language.  The hla request is usually invoked by the troffrc file to set up  a
              default language.

       .hlm n Set  the  maximum  number  of  consecutive  hyphenated  lines to n.  If n is negative, there is no
              maximum.  The default value is -1.  This value is associated with the current  environment.   Only
              lines  output  from  an  environment  count  towards the maximum associated with that environment.
              Hyphens resulting from \% are counted; explicit hyphens are not.

       .hpf file
              Read hyphenation patterns from file; this is searched for  in  the  same  way  that  name.tmac  is
              searched  for when the -mname option is specified.  It should have the same format as (simple) TeX
              patterns files.  More specifically, the following scanning rules are implemented.

              •      A percent sign starts a comment (up to  the  end  of  the  line)  even  if  preceded  by  a
                     backslash.

              •      No support for ‘digraphs’ like \$.

              •      ^^xx  (x  is  0–9  or a–f) and ^^x (character code of x in the range 0–127) are recognized;
                     other use of ^ causes an error.

              •      No macro expansion.

              •      hpf checks for the expression \patterns{...} (possibly with whitespace before and after the
                     braces).  Everything between the braces is taken as  hyphenation  patterns.   Consequently,
                     { and } are not allowed in patterns.

              •      Similarly, \hyphenation{...} gives a list of hyphenation exceptions.

              •      \endinput is recognized also.

              •      For  backwards  compatibility, if \patterns is missing, the whole file is treated as a list
                     of hyphenation patterns (only recognizing the % character as the start of a comment).

              Use the hpfcode request to map the encoding used in hyphenation patterns files  to  groff's  input
              encoding.   By  default,  everything  maps to itself except letters ‘A’ to ‘Z’ which map to ‘a’ to
              ‘z’.

              The set of hyphenation patterns is associated with the current language set by  the  hla  request.
              The  hpf  request  is usually invoked by the troffrc file; a second call replaces the old patterns
              with the new ones.

       .hpfa file
              The same as hpf except that the hyphenation patterns  from  file  are  appended  to  the  patterns
              already loaded in the current language.

       .hpfcode a b c d ...
              After  reading  a  hyphenation  patterns file with the hpf or hpfa request, convert all characters
              with character code a in the recently read patterns to character code b, character code  c  to  d,
              etc.  Initially, all character codes map to themselves.  The arguments of hpfcode must be integers
              in  the range 0 to 255.  Note that it is even possible to use character codes which are invalid in
              groff otherwise.

       .hym n Set the hyphenation margin to n: when the current adjustment mode  is  not  b,  the  line  is  not
              hyphenated if the line is no more than n short.  The default hyphenation margin is 0.  The default
              scaling  indicator  for  this request is m.  The hyphenation margin is associated with the current
              environment.  The current hyphenation margin is available in the \n[.hym] register.

       .hys n Set the hyphenation space to n: When the current adjustment mode is b don't hyphenate the line  if
              the  line  can  be justified by adding no more than n extra space to each word space.  The default
              hyphenation space is 0.  The default scaling indicator for this request  is  m.   The  hyphenation
              space  is  associated with the current environment.  The current hyphenation space is available in
              the \n[.hys] register.

       .itc n macro
              Variant of .it for which a line interrupted with \c is not counted as an input line.

       .kern n
              If n is non-zero or missing, enable pairwise kerning, otherwise disable it.

       .length xx string
              Compute the length of string and return it in the number register xx  (which  is  not  necessarily
              defined before).

       .linetabs n
              If  n  is non-zero or missing, enable line-tabs mode, otherwise disable it (which is the default).
              In line-tabs mode, tab distances are computed relative to the (current)  output  line.   Otherwise
              they are taken relative to the input line.  For example, the following

                     .ds x a\t\c
                     .ds y b\t\c
                     .ds z c
                     .ta 1i 3i
                     \*x
                     \*y
                     \*z

              yields

                     a         b         c

              In line-tabs mode, the same code gives

                     a         b                   c

              Line-tabs  mode  is  associated  with  the  current  environment;  the  read-only  number register
              \n[.linetabs] is set to 1 if in line-tabs mode, and 0 otherwise.

       .lsm xx
              Set the leading spaces macro to xx.  If there are leading spaces in an input line, it  is  invoked
              instead  of  the  usual  troff  behaviour;  the leading spaces are removed.  Registers \n[lsn] and
              \n[lss] hold the number  of  removed  leading  spaces  and  the  corresponding  horizontal  space,
              respectively.

       .mso file
              The same as the so request except that file is searched for in the same directories as macro files
              for  the  -m  command-line  option.  If the file name to be included has the form name.tmac and it
              isn't found, mso tries to include tmac.name instead and vice versa.  A warning  of  type  file  is
              generated if file can't be loaded, and the request is ignored.

       .nop anything
              Execute anything.  This is similar to ‘.if 1’.

       .nroff Make the n built-in condition true and the t built-in condition false.  This can be reversed using
              the troff request.

       .open stream filename
              Open  filename  for writing and associate the stream named stream with it.  See also the close and
              write requests.

       .opena stream filename
              Like open, but if filename exists, append to it instead of truncating it.

       .output string
              Emit string directly to the intermediate output (subject to  copy-mode  interpretation);  this  is
              similar  to  \! used at the top level.  An initial double quote in string is stripped off to allow
              initial blanks.

       .pev   Print the current environment and each defined environment state on stderr.

       .pnr   Print the names and contents of all currently defined number registers on stderr.

       .psbb filename
              Get the bounding box of a PostScript image filename.  This file must conform to  Adobe's  Document
              Structuring Conventions; the command looks for a %%BoundingBox comment to extract the bounding box
              values.   After  a  successful  call,  the coordinates (in PostScript units) of the lower left and
              upper right corner can  be  found  in  the  registers  \n[llx],  \n[lly],  \n[urx],  and  \n[ury],
              respectively.  If some error has occurred, the four registers are set to zero.

       .pso command
              This behaves like the so request except that input comes from the standard output of command.

       .ptr   Print the names and positions of all traps (not including input line traps and diversion traps) on
              stderr.   Empty  slots  in  the  page  trap  list are printed as well, because they can affect the
              priority of subsequently planted traps.

       .pvs ±n
              Set the post-vertical line space to n; default scale indicator is p.  This value is added to  each
              line  after  it  has  been  output.   With no argument, the post-vertical line space is set to its
              previous value.

              The total vertical line spacing consists of four components: .vs and  \x  with  a  negative  value
              which  are  applied  before  the  line  is output, and .pvs and \x with a positive value which are
              applied after the line is output.

       .rchar c1 c2 ...
              Remove the definitions of glyphs c1, c2, ...  This undoes the effect of a char request.

       .return
              Within a macro, return immediately.  If called with an argument, return  twice,  namely  from  the
              current macro and from the macro one level higher.  No effect otherwise.

       .rfschar c1 c2 ...
              Remove  the  font-specific  definitions of glyphs c1, c2, ...  This undoes the effect of an fschar
              request.

       .rj
       .rj n  Right justify the next n input lines.  Without an argument right justify the next input line.  The
              number of lines to be right justified is available in the \n[.rj] register.  This implicitly  does
              .ce 0.  The ce request implicitly does .rj 0.

       .rnn xx yy
              Rename number register xx to yy.

       .schar c string
              Define  global  fallback  character  (or glyph) c to be string.  The syntax of this request is the
              same as the char request; a glyph defined with schar is searched after the list of fonts  declared
              with the special request but before the mounted special fonts.

       .shc c Set  the  soft  hyphen  character  to c.  If c is omitted, the soft hyphen character is set to the
              default \[hy].  The soft hyphen character is the glyph which is inserted when a word is hyphenated
              at a line break.  If the soft hyphen character does not exist in the font of the glyph immediately
              preceding a potential break point, then the line is not broken at that point.  Neither definitions
              (specified with the char request) nor translations (specified with the tr request) are  considered
              when finding the soft hyphen character.

       .shift n
              In  a macro, shift the arguments by n positions: argument i becomes argument i-n; arguments 1 to n
              are no longer available.  If n is missing, arguments are  shifted  by  1.   Shifting  by  negative
              amounts is currently undefined.

       .sizes s1 s2 ... sn [0]
              This command is similar to the sizes command of a DESC file.  It sets the available font sizes for
              the  current  font  to  s1,  s2, ..., sn scaled points.  The list of sizes can be terminated by an
              optional 0.  Each si can also be a range of sizes mn.  Contrary to the  font  file  command,  the
              list can't extend over more than a single line.

       .special s1 s2 ...
              Fonts  s1,  s2,  ...,  are  special  and are searched for glyphs not in the current font.  Without
              arguments, reset the list of special fonts to be empty.

       .spreadwarn limit
              Make troff emit a warning if the additional space inserted for each  space  between  words  in  an
              output line is larger or equal to limit.  A negative value is changed to zero; no argument toggles
              the  warning  on and off without changing limit.  The default scaling indicator is m.  At startup,
              spreadwarn is deactivated, and limit is set to 3m.  For example, .spreadwarn 0.2m causes a warning
              if troff must add 0.2m or more for each interword space in a line.  This request is active only if
              text is justified to both margins (using .ad b).

       .sty n f
              Associate style f with font position n.  A font position can be associated either with a  font  or
              with  a style.  The current font is the index of a font position and so is also either a font or a
              style.  When it is a style, the font that is actually used is the font the name of  which  is  the
              concatenation  of  the name of the current family and the name of the current style.  For example,
              if the current font is 1 and font position 1 is associated with  style  R  and  the  current  font
              family is T, then font TR is used.  If the current font is not a style, then the current family is
              ignored.   When  the  requests  cs, bd, tkf, uf, or fspecial are applied to a style, then they are
              applied instead to the member of the current family corresponding  to  that  style.   The  default
              family  can  be set with the -f command-line option.  The styles command in the DESC file controls
              which font positions (if any) are initially associated with styles rather than fonts.

       .substring xx n1 [n2]
              Replace the string named xx with the substring defined by  the  indices  n1  and  n2.   The  first
              character  in  the  string has index 0.  If n2 is omitted, it is taken to be equal to the string's
              length.  If the index value n1 or n2 is negative, it is counted from the end of the string,  going
              backwards:  The last character has index -1, the character before the last character has index -2,
              etc.

       .tkf f s1 n1 s2 n2
              Enable track kerning for font f.  When the current font is f the width of every glyph is increased
              by an amount between n1 and n2; when the current point size is less than or equal to s1 the  width
              is  increased by n1; when it is greater than or equal to s2 the width is increased by n2; when the
              point size is greater than or equal to s1 and less than or equal to s2 the increase in width is  a
              linear function of the point size.

       .tm1 string
              Similar  to  the tm request, string is read in copy mode and written on the standard error, but an
              initial double quote in string is stripped off to allow initial blanks.

       .tmc string
              Similar to tm1 but without writing a final newline.

       .trf filename
              Transparently output the contents of file filename.  Each line is output as  if  preceded  by  \!;
              however,  the  lines are not subject to copy-mode interpretation.  If the file does not end with a
              newline, then a newline is added.  For example, you can define a macro x containing  the  contents
              of file f, using

                     .di x
                     .trf f
                     .di

              Unlike  with  the  cf request, the file cannot contain characters, such as NUL, that are not valid
              troff input characters.

       .trin abcd
              This is the same as the tr request except that the asciify request uses  the  character  code  (if
              any) before the character translation.  Example:

                     .trin ax
                     .di xxx
                     a
                     .br
                     .di
                     .xxx
                     .trin aa
                     .asciify xxx
                     .xxx

              The result is x a.  Using tr, the result would be x x.

       .trnt abcd
              This  is  the  same  as  the  tr request except that the translations do not apply to text that is
              transparently throughput into a diversion with \!.  For example,

                     .tr ab
                     .di x
                     \!.tm a
                     .di
                     .x

              prints b; if trnt is used instead of tr it prints a.

       .troff Make the n built-in condition false, and the t built-in condition true.  This undoes the effect of
              the nroff request.

       .unformat xx
              This request ‘unformats’ the diversion xx.  Contrary  to  the  asciify  request,  which  tries  to
              convert  formatted  elements  of the diversion back to input tokens as much as possible, .unformat
              only handles tabs and spaces between words (usually caused by spaces or  newlines  in  the  input)
              specially.   The  former  are treated as if they were input tokens, and the latter are stretchable
              again.  Note that the vertical size of lines is not  preserved.   Glyph  information  (font,  font
              size, space width, etc.) is retained.  Useful in conjunction with the box and boxa requests.

       .vpt n Enable  vertical position traps if n is non-zero, disable them otherwise.  Vertical position traps
              are traps set by the wh or dt requests.  Traps set by the it request  are  not  vertical  position
              traps.   The  parameter  that  controls  whether  vertical  position  traps are enabled is global.
              Initially vertical position traps are enabled.

       .warn n
              Control warnings.  n is the sum of the numbers associated with each warning that is to be enabled;
              all other warnings are disabled.  The number associated with each warning is listed  in  troff(1).
              For  example,  .warn  0 disables all warnings, and .warn 1 disables all warnings except that about
              missing glyphs.  If n is not given, all warnings are enabled.

       .warnscale si
              Set the scaling indicator used in warnings to si.  Valid values for si are u, i, c, p, and P.   At
              startup, it is set to i.

       .while c anything
              While  condition  c  is true, accept anything as input; c can be any condition acceptable to an if
              request; anything can comprise multiple lines if the first line starts with \{ and the  last  line
              ends with \}.  See also the break and continue requests.

       .write stream anything
              Write  anything  to  the  stream named stream.  stream must previously have been the subject of an
              open request.  anything is read in copy mode; a leading " is stripped.

       .writec stream anything
              Similar to write but without writing a final newline.

       .writem stream xx
              Write the contents of the macro or string xx to the stream named stream.  stream  must  previously
              have been the subject of an open request.  xx is read in copy mode.

   Extended escape sequences
       \D'...'
              All  drawing  commands  of  groff's  intermediate  output  are  accepted.  See subsection “Drawing
              Commands” below.

   Extended requests
       .cf filename
              When used in a diversion, this embeds in the diversion an object which, when  reread,  will  cause
              the  contents  of  filename  to be transparently copied through to the output.  In Unix troff, the
              contents of filename is immediately copied through to the output regardless of whether there is  a
              current diversion; this behaviour is so anomalous that it must be considered a bug.

       .de xx yy
       .am xx yy
       .ds xx yy
       .as xx yy
              In compatibility mode, these requests behaves similar to .de1, .am1, .ds1, and .as1, respectively:
              A  ‘compatibility save’ token is inserted at the beginning, and a ‘compatibility restore’ token at
              the end, with compatibility mode switched on during execution.

       .ev xx If xx is not a number, this switches to a named environment called xx.  The environment should  be
              popped with a matching ev request without any arguments, just as for numbered environments.  There
              is  no  limit  on  the number of named environments; they are created the first time that they are
              referenced.

       .hy n  New additive values 16 and 32 are available;  the  former  enables  hyphenation  before  the  last
              character, the latter enables hyphenation after the first character.

       .ss m n
              When two arguments are given to the ss request, the second argument gives the sentence space size.
              If  the  second argument is not given, the sentence space size is the same as the word space size.
              Like the word space size, the sentence space  is  in  units  of  one  twelfth  of  the  spacewidth
              parameter  for  the  current font.  Initially both the word space size and the sentence space size
              are 12.  Contrary to Unix troff, GNU troff handles this request in nroff mode also; a given  value
              is  then  rounded  down  to  the  nearest  multiple of 12.  The sentence space size is used in two
              circumstances.  If the end of a sentence occurs at the end of a line in fill mode,  then  both  an
              inter-word space and a sentence space are added; if two spaces follow the end of a sentence in the
              middle  of  a  line,  then  the second space is a sentence space.  Note that the behaviour of Unix
              troff is exactly that exhibited by GNU troff if a  second  argument  is  never  given  to  the  ss
              request.   In  GNU  troff,  as  in  Unix  troff, you should always follow a sentence with either a
              newline or two spaces.

       .ta n1 n2 ... nn T r1 r2 ... rn
              Set tabs at positions n1, n2, ..., nn and then set tabs at nn+r1, nn+r2, ..., nn+rn  and  then  at
              nn+rn+r1, nn+rn+r2, ..., nn+rn+rn, and so on.  For example,

                     .ta T .5i

              sets tabs every half an inch.

   New number registers
       The following read-only registers are available:

       \n[.br]
              Within  a  macro  call,  it is set to 1 if the macro is called with the ‘normal’ control character
              (‘.’ by default), and set to 0 otherwise.  This allows the reliable modification of requests.

                     .als bp*orig bp
                     .de bp
                     .tm before bp
                     .ie \\n[.br] .bp*orig
                     .el 'bp*orig
                     .tm after bp
                     ..

              Using this register outside of a macro makes no sense (it always returns zero in such cases).

       \n[.C] 1 if compatibility mode is in effect, 0 otherwise.

       \n[.cdp]
              The depth of the last glyph added to the current environment.  It is positive if the glyph extends
              below the baseline.

       \n[.ce]
              The number of lines remaining to be centered, as set by the ce request.

       \n[.cht]
              The height of the last glyph added to the current  environment.   It  is  positive  if  the  glyph
              extends above the baseline.

       \n[.color]
              1 if colors are enabled, 0 otherwise.

       \n[.csk]
              The  skew  of  the last glyph added to the current environment.  The skew of a glyph is how far to
              the right of the center of a glyph the center of an accent over that glyph should be placed.

       \n[.ev]
              The name or number of the current environment.  This is a string-valued register.

       \n[.fam]
              The current font family.  This is a string-valued register.

       \n[.fn]
              The current (internal) real font name.  This is a string-valued register.  If the current font  is
              a style, the value of \n[.fn] is the proper concatenation of family and style name.

       \n[.fp]
              The number of the next free font position.

       \n[.g] Always 1.  Macros should use this to determine whether they are running under GNU troff.

       \n[.height]
              The current height of the font as set with \H.

       \n[.hla]
              The current hyphenation language as set by the hla request.

       \n[.hlc]
              The number of immediately preceding consecutive hyphenated lines.

       \n[.hlm]
              The maximum allowed number of consecutive hyphenated lines, as set by the hlm request.

       \n[.hy]
              The current hyphenation flags (as set by the hy request).

       \n[.hym]
              The current hyphenation margin (as set by the hym request).

       \n[.hys]
              The current hyphenation space (as set by the hys request).

       \n[.in]
              The indentation that applies to the current output line.

       \n[.int]
              Set to a positive value if last output line is interrupted (i.e., if it contains \c).

       \n[.kern]
              1 if pairwise kerning is enabled, 0 otherwise.

       \n[.lg]
              The current ligature mode (as set by the lg request).

       \n[.linetabs]
              The current line-tabs mode (as set by the linetabs request).

       \n[.ll]
              The line length that applies to the current output line.

       \n[.lt]
              The title length as set by the lt request.

       \n[.m] The name of the current drawing color.  This is a string-valued register.

       \n[.M] The name of the current background color.  This is a string-valued register.

       \n[.ne]
              The  amount  of  space  that  was  needed  in the last ne request that caused a trap to be sprung.
              Useful in conjunction with the \n[.trunc] register.

       \n[.ns]
              1 if no-space mode is active, 0 otherwise.

       \n[.O] The current output level as set with \O.

       \n[.P] 1 if the current page is in the output list set with -o.

       \n[.pe]
              1 during a page ejection caused by the bp request, 0 otherwise.

       \n[.pn]
              The number of the next page, either the value set by a pn request, or the number  of  the  current
              page plus 1.

       \n[.ps]
              The current point size in scaled points.

       \n[.psr]
              The last-requested point size in scaled points.

       \n[.pvs]
              The current post-vertical line space as set with the pvs request.

       \n[.rj]
              The number of lines to be right-justified as set by the rj request.

       \n[.slant]
              The slant of the current font as set with \S.

       \n[.sr]
              The last requested point size in points as a decimal fraction.  This is a string-valued register.

       \n[.ss]
       \n[.sss]
              These give the values of the parameters set by the first and second arguments of the ss request.

       \n[.sty]
              The current font style.  This is a string-valued register.

       \n[.tabs]
              A  string  representation  of  the  current tab settings suitable for use as an argument to the ta
              request.

       \n[.trunc]
              The amount of vertical space truncated by the most recently sprung vertical position trap, or,  if
              the  trap  was  sprung  by  an  ne request, minus the amount of vertical motion produced by the ne
              request.  In other words, at the point a trap is sprung, it represents the difference of what  the
              vertical  position  would  have been but for the trap, and what the vertical position actually is.
              Useful in conjunction with the \n[.ne] register.

       \n[.U] Set to 1 if in safer mode and to 0 if in unsafe mode (as given with the -U command-line option).

       \n[.vpt]
              1 if vertical position traps are enabled, 0 otherwise.

       \n[.warn]
              The sum of the numbers associated with  each  of  the  currently  enabled  warnings.   The  number
              associated with each warning is listed in troff(1).

       \n[.x] The major version number.  For example, if the version number is 1.03, then \n[.x] contains 1.

       \n[.y] The minor version number.  For example, if the version number is 1.03, then \n[.y] contains 03.

       \n[.Y] The revision number of groff.

       \n[.zoom]
              The zoom value of the current font, in multiples of 1/1000th.  Zero if no magnification.

       \n[llx]
       \n[lly]
       \n[urx]
       \n[ury]
              These  four  read/write  registers are set by the psbb request and contain the bounding box values
              (in PostScript units) of a given PostScript image.

       The following read/write registers are set by the \w escape sequence:

       \n[rst]
       \n[rsb]
              Like the st and sb registers, but take account of the heights and depths of glyphs.

       \n[ssc]
              The amount of horizontal space (possibly negative) that should be added to the last glyph before a
              subscript.

       \n[skw]
              How far to right of the center of the last glyph in the \w argument, the center of an accent  from
              a roman font should be placed over that glyph.

       Other available read/write number registers are:

       \n[c.] The current input line number.  \n[.c] is a read-only alias to this register.

       \n[hours]
              The number of hours past midnight.  Initialized at start-up.

       \n[hp] The current horizontal position at input line.

       \n[lsn]
       \n[lss]
              If  there  are  leading spaces in an input line, these registers hold the number of leading spaces
              and the corresponding horizontal space, respectively.

       \n[minutes]
              The number of minutes after the hour.  Initialized at start-up.

       \n[seconds]
              The number of seconds after the minute.  Initialized at start-up.

       \n[systat]
              The return value of the system() function executed by the last sy request.

       \n[slimit]
              If greater than 0, the maximum number of objects on the input stack.  If less than or equal to  0,
              there  is  no  limit  on  the  number of objects on the input stack.  With no limit, recursion can
              continue until virtual memory is exhausted.

       \n[year]
              The current year.  Note that the traditional troff number register  \n[yr]  is  the  current  year
              minus 1900.

   Miscellaneous
       troff  predefines  a single (read/write) string-based register, \*[.T], which contains the argument given
       to the -T command-line option, namely the current output device (for example,  latin1  or  ascii).   Note
       that  this is not the same as the (read-only) number register \n[.T] which is defined to be 1 if troff is
       called with the -T command-line option, and zero otherwise.  This behaviour is different from Unix troff.

       Fonts not listed in the DESC file are automatically mounted on the next available font position when they
       are referenced.  If a font is to be mounted explicitly with the fp request on an unused font position, it
       should be mounted on the first unused font position, which can be found in the \n[.fp] register; although
       troff does not enforce this strictly, it does not allow a font to be mounted at a position  whose  number
       is much greater than that of any currently used position.

       Interpolating  a string does not hide existing macro arguments.  Thus in a macro, a more efficient way of
       doing

              .xx \\$@

       is

              \\*[xx]\\

       If the font description file contains pairwise kerning information, glyphs from  that  font  are  kerned.
       Kerning between two glyphs can be inhibited by placing a \& between them.

       In  a  string  comparison  in  a condition, characters that appear at different input levels to the first
       delimiter character are not recognized as the second or third delimiters.  This applies also  to  the  tl
       request.   In  a  \w escape sequence, a character that appears at a different input level to the starting
       delimiter character is not recognized as the closing delimiter character.  The same is true for  \A,  \b,
       \B,  \C,  \l,  \L,  \o, \X, and \Z.  When decoding a macro or string argument that is delimited by double
       quotes, a character that appears at a different input level to the starting delimiter  character  is  not
       recognized  as the closing delimiter character.  The implementation of \$@ ensures that the double quotes
       surrounding an argument appear at the same input level, which is different to  the  input  level  of  the
       argument  itself.  In a long escape name ] is not recognized as a closing delimiter except when it occurs
       at the same input level as the opening [.  In compatibility mode, no attention  is  paid  to  the  input-
       level.

       There are some new types of condition:

       .if rxxx
              True if there is a number register named xxx.

       .if dxxx
              True if there is a string, macro, diversion, or request named xxx.

       .if mxxx
              True if there is a color named xxx.

       .if cch
              True  if  there is a character (or glyph) ch available; ch is either an ASCII character or a glyph
              (special character) \N'xxx', \(xx or \[xxx]; the condition is also true if ch has been defined  by
              the char request.

       .if Ff True  if  font  f  exists.   f  is  handled as if it was opened with the ft request (this is, font
              translation and styles are applied), without actually mounting it.

       .if Ss True if style s has been registered.  Font translation is applied.

       The tr request can now map characters onto \~.

       The space width emitted by the \| and \^ escape sequences can be controlled  on  a  per-font  basis.   If
       there  is  a glyph named \| or \^, respectively (note the leading backslash), defined in the current font
       file, use this glyph's width instead of the default value.

       It is now possible to have whitespace between the first and second dot (or the name of the ending  macro)
       to end a macro definition.  Example:

              .if t \{\
              .  de bar
              .    nop Hello, I'm ‘bar’.
              .  .
              .\}

INTERMEDIATE OUTPUT FORMAT

       This  section  describes  the  format  output  by GNU troff.  The output format used by GNU troff is very
       similar to that used by Unix device-independent troff.  Only the differences are documented here.

   Units
       The argument to the s command is in scaled points (units of points/n, where n  is  the  argument  to  the
       sizescale command  in the DESC file).  The argument to the x Height command is also in scaled points.

   Text Commands
       Nn     Print glyph with index n (a non-negative integer) of the current font.

       If the tcommand line is present in the DESC file, troff uses the following two commands.

       txxx   xxx  is any sequence of characters terminated by a space or a newline (to be more precise, it is a
              sequence of glyphs which are accessed with the  corresponding  characters);  the  first  character
              should  be printed at the current position, the current horizontal position should be increased by
              the width of the first character, and so on for each character.  The width of the  glyph  is  that
              given in the font file, appropriately scaled for the current point size, and rounded so that it is
              a multiple of the horizontal resolution.  Special characters cannot be printed using this command.

       un xxx This  is  same  as the t command except that after printing each character, the current horizontal
              position is increased by the sum of the width of that character and n.

       Note that single characters can have the  eighth  bit  set,  as  can  the  names  of  fonts  and  special
       characters.

       The  names  of  glyphs and fonts can be of arbitrary length; drivers should not assume that they are only
       two characters long.

       When a glyph is to be printed, that glyph is always  in  the  current  font.   Unlike  device-independent
       troff, it is not necessary for drivers to search special fonts to find a glyph.

       For color support, some new commands have been added:

       mc cyan magenta yellow
       md
       mg gray
       mk cyan magenta yellow black
       mr red green blue
              Set the color components of the current drawing color, using various color schemes.  md resets the
              drawing color to the default value.  The arguments are integers in the range 0 to 65536.

       The x device control command has been extended.

       x u n  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.

   Drawing Commands
       The D drawing command has been extended.  These extensions are not used by GNU pic if the  -n  option  is
       given.

       Df n\n Set  the  shade  of gray to be used for filling solid objects to n; n must be an integer between 0
              and 1000, where 0 corresponds solid  white  and  1000  to  solid  black,  and  values  in  between
              correspond to intermediate shades of gray.  This applies only to solid circles, solid ellipses and
              solid  polygons.   By  default,  a  level  of 1000 is used.  Whatever color a solid object has, it
              should completely obscure everything beneath it.  A value greater than 1000 or  less  than  0  can
              also  be  used:  this means fill with the shade of gray that is currently being used for lines and
              text.  Normally this is black, but some drivers may provide a way of changing this.

              The corresponding \D'f...' command shouldn't be used since its argument is always  rounded  to  an
              integer multiple of the horizontal resolution which can lead to surprising results.

       DC d\n Draw a solid circle with a diameter of d with the leftmost point at the current position.

       DE dx dy\n
              Draw  a  solid  ellipse  with  a  horizontal diameter of dx and a vertical diameter of dy with the
              leftmost point at the current position.

       Dp dx1 dy1 dx2 dy2 ... .lf 3500
              dxn dyn\n Draw a  polygon  with,  for  i=1,...,n+1,  the  i-th  vertex  at  the  current  position
--

INCOMPATIBILITIES

       In  spite  of the many extensions, groff has retained compatibility to classical troff to a large degree.
       For the cases where the extensions lead to collisions, a special compatibility mode with the  restricted,
       old functionality was created for groff.

   Groff Language
       groff  provides  a compatibility mode that allows the processing of roff code written for classical troff
       or for other implementations of roff in a consistent way.

       Compatibility mode can be turned on with the -C command-line option, and turned on or off  with  the  .cp
       request.  The number register \n(.C is 1 if compatibility mode is on, 0 otherwise.

       This  became  necessary  because the GNU concept for long names causes some incompatibilities.  Classical
       troff interprets

              .dsabcd

       as defining a string ab with contents cd.  In groff mode, this is considered as a call of a  macro  named
       dsabcd.

       Also  classical  troff  interprets \*[ or \n[ as references to a string or number register called [ while
       groff takes this as the start of a long name.

       In compatibility mode, groff interprets these things in the  traditional  way;  so  long  names  are  not
       recognized.

       On  the  other  hand,  groff  in  GNU  native  mode does not allow to use the single-character escapes \\
       (backslash), \| (vertical bar), \^ (caret), \& (ampersand), \{ (opening brace), \} (closing brace),  ‘\ ’
       (space),  \'  (single quote), \` (backquote), \- (minus), \_ (underline), \! (bang), \% (percent), and \c
       (character c) in names of strings, macros, diversions, number registers, fonts or  environments,  whereas
       classical troff does.

       The \A escape sequence can be helpful in avoiding these escape sequences in names.

       Fractional  point sizes cause one noteworthy incompatibility.  In classical troff, the ps request ignores
       scale indicators and so

              .ps 10u

       sets the point size to 10 points, whereas in groff native mode the point size is set to 10 scaled points.

       In groff, there is a fundamental difference between unformatted input characters,  and  formatted  output
       characters  (glyphs).   Everything  that  affects  how a glyph is output is stored with the glyph; once a
       glyph has been constructed it is unaffected by any subsequent requests that are executed,  including  the
       bd, cs, tkf, tr, or fp requests.

       Normally glyphs are constructed from input characters at the moment immediately before the glyph is added
       to  the  current  output line.  Macros, diversions and strings are all, in fact, the same type of object;
       they contain lists of input characters and glyphs in any combination.

       Special characters can be both; before being added to the output, they act as input entities,  afterwards
       they denote glyphs.

       A glyph does not behave like an input character for the purposes of macro processing; it does not inherit
       any of the special properties that the input character from which it was constructed might have had.  The
       following example makes things clearer.

              .di x
              \\\\
              .br
              .di
              .x

       With  GNU  troff  this  is printed as \\.  So each pair of input backslashes ‘\\’ is turned into a single
       output backslash glyph ‘\’ and the resulting output backslashes are not interpreted as escape  characters
       when they are reread.

       Classical troff would interpret them as escape characters when they were reread and would end up printing
       a single backslash ‘\’.

       In  GNU,  the  correct  way  to get a printable version of the backslash character ’\’ is the \(rs escape
       sequence, but classical troff does not provide a clean feature for getting a  non-syntactical  backslash.
       A  close  method  is  the printable version of the current escape character using the \e escape sequence;
       this works if the current escape character is not redefined.  It works in both GNU mode and compatibility
       mode, while dirty tricks like specifying a sequence of multiple backslashes do not work reliably; for the
       different handling in diversions, macro definitions, or text mode quickly leads to a confusion about  the
       necessary number of backslashes.

       To  store  an escape sequence in a diversion that is interpreted when the diversion is reread, either the
       traditional \! transparent output facility or the new \? escape sequence can be used.

   Intermediate Output
       The groff intermediate output format is in a state of evolution.  So far it has  some  incompatibilities,
       but  it is intended to establish a full compatibility to the classical troff output format.  Actually the
       following incompatibilities exist:

       • The positioning after the drawing of the polygons conflicts with the classical definition.

       • The intermediate output cannot be rescaled to other devices  as  classical  ‘device-independent’  troff
         did.

AUTHORS

       This document was written by James Clark and modified by Werner Lemberg and Bernd Warken.

SEE ALSO

       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”.

       groff(1)
              A list of all documentation around groff.

       groff(7)
              A description of the groff language, including a short, but complete reference of  all  predefined
              requests, registers, and escapes of plain groff.  From the command line, this is called using

                     man 7 groff

       roff(7)
              A survey of roff systems, including pointers to further historical documentation.

       [CSTR #54]
              The Nroff/Troff User's Manual by J. F. Ossanna of 1976 in the revision of Brian Kernighan of 1992,
              being the classical troff documentation.

groff 1.22.4                                      23 March 2022                                    GROFF_DIFF(7)