Provided by: groff_1.21-7_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
       User's 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
       \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 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.

       \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] 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.

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

              o      No support for `digraphs' like \$.

              o      ^^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.

              o      No macro expansion.

              o      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.

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

              o      \endinput is recognized also.

              o      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  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.

       .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 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 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[.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  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 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 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)
              \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.  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

              \D'c  $x sub 1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x sub n$ $y
              sub n$'

       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:

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

       o 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,
       2010 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   <http://www.gnu.org/copyleft/fdl.html>.    This
       document was written by  James  Clark,  with  modifications  by  Werner
       Lemberg <wl@gnu.org> and Bernd Warken <bwarken@mayn.de>.

       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 User's Manual by J. F. Ossanna of  1976  in  the
              revision  of  Brian Kernighan of 1992, being the classical troff
              documentation <http://cm.bell-labs.com/cm/cs/cstr/54.ps.gz>.