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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 includes  the  roff  lan‐
       guage 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 font family (note that \FP won't
	      work; it selects font family `P' instead).

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

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

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

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

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

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

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

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

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

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

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

	      128    Prohibit  a  line break before the character, but allow a
		     line break after the character.  This works only in  com‐
		     bination  with flags 256 and 512 and has no effect other‐
		     wise.

	      256    Prohibit a line break after the character,	 but  allow  a
		     line break before the character.  This works only in com‐
		     bination with flags 128 and 512 and has no effect	other‐
		     wise.

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

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

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

	      Define entity c to be string.  To be more	 precise,  define  (or
	      even  override) a groff entity which can be accessed with name c
	      on the input side, and which uses string	on  the	 output	 side.
	      Every time glyph c needs to be printed, string is processed in a
	      temporary environment and the result is wrapped up into a single
	      object.  Compatibility mode is turned off and the escape 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.

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

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

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

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

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

       .cp n  If n is non-zero or missing, enable compatibility	 mode,	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, and so on.  A hyphenation code must be a single input
	      character (not a special character) other	 than  a  digit	 or  a
	      space.   Initially  each lower-case letter a-z has a hyphenation
	      code, which is itself, and each  upper-case  letter  A-Z	has  a
	      hyphenation code which is the lower-case version of itself.  See
	      also the hpf request.

       .hla lang
	      Set the  current	hyphenation  language  to  lang.   Hyphenation
	      exceptions  specified  with  the hw request and hyphenation 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.	  By  default,	every‐
	      thing  maps to itself except letters `A' to `Z' which map to `a'
	      to `z'.

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

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

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

       .nop anything
	      Execute anything.	 This is similar to `.if 1'.

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

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

       .opena stream filename
	      Like open, but if filename exists, append to it instead of 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.  Con‐
	      trary 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  spe‐
	      cial 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[.O] The current output level as set with \O.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       \n[skw]
	      How far to right of the center of the last glyph in the \w 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[lsn]
       \n[lss]
	      If  there	 are  leading spaces in an input line, these registers
	      hold the number of leading spaces and the corresponding horizon‐
	      tal space, respectively.

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

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

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

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

       \n[year]
	      The current year.	 Note that the traditional troff number 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, 2001-2004, 2006-2010, 2012  Free  Software  Founda‐
       tion, 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 ⟨groff-bernd.warken-72@web.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 1.22.2		7 February 2013			 GROFF_DIFF(7)
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