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GROFF_DIFF(7)							 GROFF_DIFF(7)

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 Osanna 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 clas‐
       sical Unix 7 troff are described in detail.

   Long names
       The  names  of number registers, fonts, strings/macros/diversions, spe‐
       cial characters (glyphs), and colors can be of any length.   In	escape
       sequences,  additionally	 to  the classical (xx construction for a two-
       character 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.	 Exam‐
	      ple:  `\[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 list of glyph name components used compos‐
	      ite glyph names.

       \f[xxx]
	      Set  font xxx.  Additionally, \f[] is a new syntax 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 pointsizes
       A scaled point is equal to 1/sizescale points, where sizescale is spec‐
       ified  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 pointsize 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 argu‐
       ment 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 will be
       equivalent to  a	 millipoint;  the  call	 .ps 10.25  is	equivalent  to
       .ps 10.25z  and	so sets the pointsize to 10250 scaled points, which is
       equal to 10.25 points.

       The number register \n[.s] returns the pointsize in points  as  decimal
       fraction.  There is also a new number register \n[.ps] that returns the
       pointsize 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	 scal‐
       ing  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 resp., depending on whether anything is
	      or is not acceptable as the name of a string, macro,  diversion,
	      number  register, environment, font, or color.  It will return 0
	      if anything is empty.  This is useful if you want to lookup user
	      input in some sort of associative table.

       \B'anything'
	      This  expands  to 1 or 0 resp., depending on whether anything is
	      or is not a valid numeric expression.  It will return 0 if  any‐
	      thing 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 inter‐
	      preted 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 will 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 will not be 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]  Suppressing  troff  output.   The escapes \02, \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 will start 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	speci‐
		     fied  and must be one of l, r, c, or i (left, right, cen‐
		     tered, inline).  filename will  be	 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 exten‐
	      sion to the UNIX troff output format, and will  confuse  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.

       \$(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 will transparently embed anything
	      in  the  diversion.   anything  is  read in copy mode.  When the
	      diversion is reread, anything will be interpreted.  anything may
	      not  contain newlines; use \! if you want to embed newlines in a
	      diversion.  The escape sequence \? is also  recognised  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

	      will print 4.

       \/     This increases the width of the  preceding  glyph	 so  that  the
	      spacing  between that glyph and the following glyph will be cor‐
	      rect if the following glyph is a roman glyph.  It is a good idea
	      to  use this escape sequence whenever an italic glyph is immedi‐
	      ately 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 will 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
	      character.

       \#     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 will be  exactly  equivalent.   If	yy  is
	      undefined,  a  warning  of  type	reg will be generated, and the
	      request will be ignored.

       .als xx yy
	      Create an alias xx for  request,	string,	 macro,	 or  diversion
	      object  named yy.	 The new name and the old name will be exactly
	      equivalent (it is similar to a hard rather than  a  soft	link).
	      If yy is undefined, a warning of type mac will be generated, and
	      the request will be ignored.  The de, am, di,  da,  ds,  and  as
	      requests	only  create  a	 new  object if the name of the macro,
	      diversion or string diversion 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 `compati‐
	      bility  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  compatibil‐
	      ity  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 will  be  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

	      will  set	 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  will	be 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 will not become part of
	      the diversion (i.e., the diversion  always  starts  with	a  new
	      line)  but  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 will not be broken
		     at	 a  character with this property unless the characters
		     on each side both have non-zero hyphenation codes.

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

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

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

	      32     An end-of-sentence character followed by  any  number  of
		     characters	 with this property will be 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  hav‐
		     ing  a  zero  space  factor  in TeX (initially characters
		     "')]*\(dg\(rq have this property).

       .char c string
	      Define glyph c to be string.  Every time glyph  c	 needs	to  be
	      printed, string will be processed in a temporary environment and
	      the result will be wrapped up into a single object.  Compatibil‐
	      ity mode will be turned off and the escape character will be set
	      to \ while string is being processed.  Any emboldening, constant
	      spacing  or  track kerning will be applied to this object rather
	      than to individual glyphs in string.

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

	      There  is	 a special anti-recursion feature: Use of glyph within
	      the glyph's definition will be 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, other‐
	      wise disable it.	In compatibility  mode,	 long  names  are  not
	      recognised,  and	the  incompatibilities caused by long names do
	      not arise.

       .defcolor xxx scheme color_components
	      Define color.  scheme can be one of the  following  values:  rgb
	      (three  components),  cym	 (three components), cmyk (four compo‐
	      nents), 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 spec‐
	      ify 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.

       .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 will be 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 fam‐
	      ilies.

       .fchar c string
	      Define fallback 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 previ‐
	      ous fill color.

       .fschar f c string
	      Define fallback 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,...  will  be  special,
	      that  is, they will searched for glyphs not in the current font.
	      Any fonts specified in the  special  request  will  be  searched
	      after  fonts  specified  in the fspecial request.	 Without argu‐
	      ment, 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 will be used.	If g is missing, or equal to f
	      then font f will not be translated.

       .gcolor c
	      Set the glyph color to c.	 If c is missing, switch to the previ‐
	      ous 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.  Ini‐
	      tially 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  pat‐
	      terns  specified	with  the hpf request are both associated with
	      the current hyphenation language.	 The hla  request  is  usually
	      invoked by the troffrc file.

       .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 asso‐
	      ciated  with  that  environment.	 Hyphens resulting from \% are
	      counted; explicit hyphens are not.

       .hpf file
	      Read hyphenation patterns from file; this will be	 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 com‐
		     ment).

	      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 pat‐
	      terns 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 lan‐
	      guage.

       .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 will not be 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 hyphen‐
	      ation margin is associated with the  current  environment.   The
	      current  hyphenation  margin is available in the \n[.hym] regis‐
	      ter.

       .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	regis‐
	      ter 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  dis‐
	      tances are computed relative to the (current) output line.  Oth‐
	      erwise 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 trun‐
	      cating 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.

       .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	bound‐
	      ing  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 will be 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 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 spe‐
	      cial request but before the mounted special fonts.

       .shc c Set  the	soft hyphen character to c.  If c is omitted, the soft
	      hyphen character will be set to  the  default  \(hy.   The  soft
	      hyphen character is the glyph which will be 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 will not be 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 will no longer be	avail‐
	      able.   If n is missing, arguments will be shifted by 1.	Shift‐
	      ing 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 will be 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  will
	      cause  a	warning if troff must add 0.2m or more for each inter‐
	      word 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 exam‐
	      ple,  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 will
	      be  used.	  If the current font is not a style, then the current
	      family is ignored.  When the requests cs, bd, tkf, uf, or	 fspe‐
	      cial  are	 applied to a style, then they will instead be applied
	      to the member of the current family corresponding to that style.
	      The  default  family  can be set with the -f 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
	      will be counted from the end of the string, going backwards: The
	      last character has index -1, the character before the last char‐
	      acter 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 will be increased by an amount  between  n1
	      and  n2; when the current point size is less than or equal to s1
	      the width will be increased by n1; when it is  greater  than  or
	      equal  to	 s2  the width will be 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 writ‐
	      ten 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  sub‐
	      ject to copy-mode interpretation.	 If the file does not end with
	      a newline, then a newline will be 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 legal troff input characters.

       .trin abcd
	      This is the same as the  tr  request  except  that  the  asciify
	      request  will use the character code (if any) before the charac‐
	      ter 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

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

       .troff Make the n built-in condition false, and the t  built-in	condi‐
	      tion 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, .unfor‐
	      mat will only handle tabs	 and  spaces  between  words  (usually
	      caused  by spaces or newlines in the input) specially.  The for‐
	      mer 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 posi‐
	      tion  traps.  The parameter that controls whether vertical posi‐
	      tion 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  will  be
	      disabled.	  The number associated with each warning is listed in
	      troff(1).	 For example, .warn 0 will disable all	warnings,  and
	      .warn  1	will  disable  all  warnings except that about missing
	      glyphs.  If n is not given, all warnings will be 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	previ‐
	      ously  have  been	 the  subject of an open request.  anything is
	      read in copy mode; a leading " will be 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 infor‐
	      mation.

   Extended requests
       .cf filename
	      When used in a diversion, this will embed 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 will switch to a named environment
	      called xx.  The environment should be popped with a matching  ev
	      request  without	any  arguments,	 just as for numbered environ‐
	      ments.  There is no limit on the number of  named	 environments;
	      they will be created the first time that they are referenced.

       .ss m n
	      When two arguments are given to the ss request, the second argu‐
	      ment gives the sentence space size.  If the second  argument  is
	      not  given, the sentence space size will be 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 will be added; if two spaces follow the end of  a
	      sentence	in the middle of a line, then the second space will be
	      a sentence space.	 Note that the behaviour of UNIX troff will be
	      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

	      will set tabs every half an inch.

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

       \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 indent 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-val‐
	      ued 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 pointsize in scaled points.

       \n[.psr]
	      The last-requested pointsize 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  pointsize 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] will contain 1.

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

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

       \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	 Post‐
	      Script 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 argu‐
	      ment, 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 regis‐
	      ter \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 will 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 will be kerned.	Kerning between two glyphs can
       be inhibited by placing a \& between them.

       In a string comparison in a condition, characters that appear  at  dif‐
       ferent input levels to the first delimiter character will not be recog‐
       nised as the second or third delimiters.	 This applies also to  the  tl
       request.	  In  a \w escape sequence, a character that appears at a dif‐
       ferent input level to the starting  delimiter  character	 will  not  be
       recognised  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
       will  not be recognised as the closing delimiter character.  The imple‐
       mentation of \$@ ensures that the double quotes surrounding an argument
       will  appear the same input level, which will be different to the input
       level of the argument itself.  In a long escape name ] will not be rec‐
       ognized	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 glyph ch available; ch	 is  either  an	 ASCII
	      character	 or  a	glyph  (special character) \(xx or \[xxx]; the
	      condition will also be 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 \~.

       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 for‐
       mat used by GNU troff is very similar to that used by Unix device-inde‐
       pendent 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	will  use  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 char‐
	      acter 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 will be only two characters long.

       When a glyph is to be printed, that glyph will always be 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 under‐
	      lining 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 will not be
       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  cor‐
	      respond  to  intermediate	 shades of gray.  This applies only to
	      solid circles, solid ellipses and solid polygons.	 By default, a
	      level  of 1000 will be 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 will be 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 hori‐
	      zontal 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 ver‐
	      tical diameter of dy with the  leftmost  point  at  the  current
	      position.

       Dp dx1 dy1 dx2 dy2 ... dxn dyn\n
	      Draw  a  polygon	with,  for i=1,...,n+1, the i-th vertex at the
	      current position +jΣ1(dxj,dyj).  At the  moment,	GNU  pic  only
	      uses this command to generate triangles and rectangles.

       DP dx1 dy1 dx2 dy2 ... dxn dyn\n
	      Like Dp but draw a solid rather than outlined polygon.

       Dt n\n Set  the	current line thickness to n machine units.  Tradition‐
	      ally 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 x1 y1 x2 y2 ... xn yn′

       where  c	 is not one of c, e, l, a, or ~, Unix troff will treat each of
       the xi as a horizontal quantity, and each of the yi as a vertical quan‐
       tity  and  will assume that the width of the drawn object is iΣ1xi, and
       that the height is iΣ1yi.  (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 x1 y1 x2 y2 ... xn yn\n

       the current position should be increased by (iΣ1xi,iΣ1yi).

       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 will follow each newline in the argument with  a
       +  character  (as  usual,  it will terminate 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 com‐
       mand 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 will  be
       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 pointsizes cause one noteworthy incompatibility.  In classi‐
       cal troff, the ps request ignores scale indicators and so

	      .ps 10u

       will set the pointsize to 10 points, whereas in groff native  mode  the
       pointsize will be 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  will be 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 combi‐
       nation.

       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 will make things clearer.

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

       With GNU troff this will be printed as \\.  So each pair of input back‐
       slashes ‘\\’ 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 charac‐
       ter is not redefined.  It works in  both	 GNU  mode  and	 compatibility
       mode,  while  dirty tricks like specifying a sequence of multiple back‐
       slashes 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	 will  be  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	 clas‐
	 sical "device-independent" troff did.

AUTHORS
       Copyright  (C)  1989,  2001, 2002, 2003, 2004 Free Software Foundation,
       Inc.

       This document is distributed under the terms of the FDL (GNU Free Docu‐
       mentation  License)  version  1.1 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 com‐
	      plete  reference	of  all	 predefined  requests,	registers, and
	      escapes of plain groff.  From the command line, this  is	called
	      using

	      shell# man 7 groff

       roff(7)
	      A survey of roff systems, including pointers to further histori‐
	      cal documentation.

       [CSTR #54]
	      The Nroff/Troff User's Manual by J. F. Osanna  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⟩.

Groff Version 1.19.2		20 October 2005			 GROFF_DIFF(7)
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