Provided by: groff_1.20.1-7_i386 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
       Users Manual by Ossanna and Kernighan.  This inludes the roff language
       as well as the intermediate output format (troff output).

       The  section SEE ALSO 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 the groff info file for
              details 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
       \Aanything’
              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.

       \Banything’
              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.

       \Cxxx’
              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  color  (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.

       \Nn’  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.

       \Rname 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.

       \Zanything’
              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] 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).

       .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.

       .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.  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.

              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 counts as
              one 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.

       .mso file
              The same as the so request except that file is searched  for  in
              the  same directories as macro files for the 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.

       .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 a 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 m-n.
              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  for  more
              information.

   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.

       .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 are
              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 to reliably modify 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[.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  a
              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 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[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 to 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)
              \Nxxx’,  \(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 \Df...’  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.  delim $$

       Dp $dx sub 1$ $dy sub 1$ $dx sub 2$ $dy sub 2$ $...$ $dx sub n$ $dy sub
       n$\n
              Draw  a  polygon with, for $i = 1 ,..., n+1$, the i-th vertex at
              the current position $+ sum from j=1 to i-1 ( dx sub j , dy  sub
              j )$.  At the moment, GNU pic only uses this command to generate
              triangles and rectangles.

       DP $dx sub 1$ $dy sub 1$ $dx sub 2$ $dy sub 2$ $...$ $dx sub n$ $dy sub
       n$\n
              Like Dp but draw a solid rather than outlined polygon.

       Dt n\n Set  the  current   line   thickness   to   n   machine   units.
              Traditionally   Unix   troff   drivers   use  a  line  thickness
              proportional to the current point size; drivers should  continue
              to  do  this if no Dt command has been given, or if a Dt command
              has been given with a negative value of n.  A zero  value  of  n
              selects the smallest available line thickness.

       A difficulty arises in how the current position should be changed after
       the execution of these commands.  This is not of great importance since
       the code generated by GNU pic does not depend on this.  Given a drawing
       command of the form

              \Dc $x sub 1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x sub n$  $y
              sub n$’

       where  c  is not one of c, e, l, a, or ~, Unix troff treats each of the
       $x sub i$ as a horizontal quantity, and each of the  $y  sub  i$  as  a
       vertical  quantity  and  assumes  that the width of the drawn object is
       $sum from i=1 to n x sub i$, and that the height is $sum from i=1 to  n
       y  sub  i$.   (The assumption about the height can be seen by examining
       the st and sb registers after using such a D command  in  a  \w  escape
       sequence).   This rule also holds for all the original drawing commands
       with the exception of De.  For the sake of compatibility GNU troff also
       follows  this  rule, even though it produces an ugly result in the case
       of the Dt and Df, and, to a lesser extent,  DE  commands.   Thus  after
       executing a D command of the form

              Dc  $x  sub  1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x sub n$ $y
              sub n$\n

       the current position should be increased by $( sum from i=1 to n x  sub
       i , sum from i=1 to n y sub i )$.

       Another set of extensions is

       DFc cyan magenta yellow\n
              DFd\n  DFg  gray\n DFk cyan magenta yellow black\n DFr red green
              blue\n Set the color components of the filling color similar  to
              the m commands above.

       The  current  position isn’t changed by those colour commands (contrary
       to Df).

   Device Control Commands
       There is a continuation convention which permits the  argument  to  the
       x X  command  to  contain newlines: when outputting the argument to the
       x X command, GNU troff follows each newline in the argument  with  a  +
       character (as usual, it terminates the entire argument with a newline);
       thus if the line after the line containing the x X command starts  with
       +,  then  the newline ending the line containing the x X command should
       be treated as part of the argument to the x X command, the + should  be
       ignored,  and  the  part  of the line following the + should be treated
       like the part of the line following the x X command.

       The first three output commands are guaranteed to be:

              x T device
              x res n h v
              x init

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 to process 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

       Copyright (C) 1989, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009 Free
       Software Foundation, Inc.

       This document is distributed under the  terms  of  the  FDL  (GNU  Free
       Documentation  License) version 1.3 or later.  You should have received
       a copy of the FDL on your system, it is also available on-line  at  the
       GNU  copyleft  site  This  document  was  written  by James Clark, with
       modifications by Werner Lemberg and Bernd Warken

       This document is part of groff, the GNU roff  distribution.   Formerly,
       the  contents  of  this  document was kept in the manual page troff(1).
       Only the parts dealing with the language aspects of the different  roff
       systems  were  carried over into this document.  The troff command line
       options and warnings are still documented in troff(1).

SEE ALSO

       The groff info file,  cf.  info(1)  presents  all  groff  documentation
       within a single document.

       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  Users  Manual by J. F. Ossanna of 1976 in the
              revision of Brian Kernighan of 1992, being the  classical  troff
              documentation