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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 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 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 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.	 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  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 spec‐
       ified in the DESC file (1 by default).  There is a  new	scale  indica‐
       tor  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  equiva‐
       lent  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 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, 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	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 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	bound‐
		     ary).

	      \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 is associated with the produc‐
		     tion 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 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 diver‐
	      sion is reread, anything is interpreted.	anything may not  con‐
	      tain  newlines; use \! if you want to embed newlines in a diver‐
	      sion.  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 fol‐
	      lowed 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	 unde‐
	      fined,  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 `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 are treated like ordinary input
	      characters when xx is reread.  Useful for diversions in conjunc‐
	      tion  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	 char‐
		     acters  -\[hy]\[em]  have	this  property); a line is not
		     broken at a character with this property unless the char‐
		     acters on each side both have non-zero hyphenation codes.

		     This can be overridden with value 64.

	      8	     The  glyph	 associated with this character overlaps hori‐
		     zontally  (initially  characters	\[ul]\[rn]\[ru]\[radi‐
		     calex]\[sqrtex] have this property).

	      16     The  glyph associated with this character overlaps verti‐
		     cally (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 charac‐
		     ters.   Use this in combination with values 2 and 4 (ini‐
		     tially no characters have this property).

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

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

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

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

	      A glyph definition can be removed with the rchar request.

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

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

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

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

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

       .cp n  If n is non-zero or missing, enable compatibility	 mode,	other‐
	      wise disable it.	In compatibility mode, long names are not rec‐
	      ognized, 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  com‐
	      ponents),	 and  gray  or grey (one component).  Color components
	      can be given either as a hexadecimal string or as positive deci‐
	      mal  integers  in	 the range 0-65535.  A hexadecimal string con‐
	      tains 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.

       .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 fam‐
	      ilies.

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

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

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

	      ·	     No support for `digraphs' like \$.

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

	      ·	     No macro expansion.

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

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

	      ·	     \endinput is recognized also.

	      ·	     For backwards compatibility, if \patterns is missing, the
		     whole  file  is treated as a list of hyphenation patterns
		     (only recognizing the % character as the start of a  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 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 hyphen‐
	      ation 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	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.

       .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 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 is added to each line after it has been out‐
	      put.  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  hyphen‐
	      ated  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	 nega‐
	      tive 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 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 is
	      used.  If the current font is not a style, then the current fam‐
	      ily  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 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 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 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  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 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 are dis‐
	      abled.  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 previ‐
	      ously 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 infor‐
	      mation.

   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 behav‐
	      iour 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  environ‐
	      ments.   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 argu‐
	      ment  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 fol‐
	      low 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-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 point size in scaled points.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       \n[skw]
	      How far to right of the center of the last glyph in the \w 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 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  dif‐
       ferent 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 dif‐
       ferent input level to the starting delimiter character  is  not	recog‐
       nized 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	 argu‐
       ment  that is delimited by double quotes, a character that appears at a
       different input level to the starting delimiter character is not recog‐
       nized  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	delim‐
       iter  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 con‐
       trolled 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 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 uses  the  fol‐
       lowing 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 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 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 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  cor‐
	      respond  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 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 treats each of the
       xi as a horizontal quantity, and each of the yi as a vertical  quantity
       and  assumes  that the width of the drawn object is iΣ1xi, and that the
       height is iΣ1yi.	 (The assumption about the height can be seen by exam‐
       ining  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 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  con‐
       sidered 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 clas‐
       sical 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 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 makes things clearer.

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

       With  GNU  troff	 this  is  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 is interpreted when the
       diversion  is  reread,  either  the  traditional	 \! transparent output
       facility or the new \? escape sequence can be used.

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

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

       · The intermediate output cannot be rescaled to other devices as	 clas‐
	 sical `device-independent' troff did.

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

       This document is distributed under the terms of the FDL (GNU Free Docu‐
       mentation  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 com‐
	      plete  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 histori‐
	      cal 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⟩.

Groff Version 1.20.1		  09 May 2010			 GROFF_DIFF(7)
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