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RedHat 9 (Linux i386) - man page for groff_diff (redhat section 7)

GROFF_DIFF(7)			 Miscellaneous Information Manual		    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 pro-
       cessing system and the classical roff formatter of the freely  available  Unix  7  of  the
       1970s,  documented  in  the Troff User's Manual by Osanna and Kernighan.  This inludes the
       roff language as well as the intermediate output format (troff output).

       The section SEE ALSO gives pointers to both the classical roff and the modern groff  docu-
       mentation.

       At  the	moment,  this  document  is the place of the most actual documentation within the
       groff system.  This might change in the future.	Actually, all novelties of the groff lan-
       guage  are  first described here and will pervade into the other documents only at a later
       stage.

GROFF LANGUAGE
       In this section, all additional features of groff compared to the classical Unix  7  troff
       are described in detail.

   Long names
       The  names  of number registers, fonts, strings/macros/diversions, special characters, and
       colors can be of any length.  In escape sequences, additionally to the classical (xx  con-
       struction  for a two character name, you can use [xxx] for a name of arbitrary length, for
       example in

       \[xxx]	 Print the special character called xxx.

       \f[xxx]	 Set font xxx.	Additionally, \f[] is a new syntax equal to \fP, i.e., to  return
		 to the previous font.

       \*[xxx arg1 arg2 ...]
		 Interpolate string xxx, taking arg1, arg2, ... as arguments.

       \n[xxx]	 Interpolate number register xxx.

   Fractional pointsizes
       A  scaled  point  is equal to 1/sizescale points, where sizescale is specified in the DESC
       file (1 by default).  There is a new scale indicator z that has the effect of  multiplying
       by sizescale.  Requests and escape sequences in troff interpret arguments that represent a
       pointsize as being in units of scaled points, but they evaluate each such argument using a
       default	scale  indicator  of z.  Arguments treated in this way are the argument to the ps
       request, the third argument to the cs request, the second and fourth arguments to the  tkf
       request,  the  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 will be equivalent to a milli-
       point;  the  call .ps 10.25 is equivalent to .ps 10.25z and so sets the pointsize to 10250
       scaled points, which is equal to 10.25 points.

       The number register \n[.s] returns the pointsize in points as decimal fraction.	There  is
       also a new number register \n[.ps] that returns the pointsize in scaled points.

       It  would make no sense to use the z scale indicator in a numeric expression whose default
       scale indicator was neither u nor z, and so troff disallows this.  Similarly it would make
       no  sense  to  use  a  scaling  indicator  other than z or u in a numeric expression whose
       default scale indicator was z, and so troff disallows this as well.

       There is also new scale indicator s which multiplies by the number of units  in	a  scaled
       point.	So,  for  example,  \n[.ps]s  is equal to 1m.  Be sure not to confuse the s and z
       scale indicators.

   Numeric expressions
       Spaces are permitted in a number expression within parentheses.

       M indicates a scale of 100ths of an em.	f indicates a scale  of  65536	units,	providing
       fractions for color definitions with the defcolor request.  For example, 0.5f = 32768u.

       e1>?e2 The maximum of e1 and e2.

       e1<?e2 The minimum of e1 and e2.

       (c;e)  Evaluate e using c as the default scaling indicator.  If c is missing, ignore scal-
	      ing indicators in the evaluation of e.

   New escape sequences
       \A'anything'
	      This expands to 1 or 0 resp., depending on whether anything is or is not acceptable
	      as  the  name of a string, macro, diversion, number register, environment, font, or
	      color.  It will return 0 if anything is empty.  This  is	useful	if  you  want  to
	      lookup user input in some sort of associative table.

       \B'anything'
	      This  expands  to  1 or 0 resp., depending on whether anything is or is not a valid
	      numeric expression.  It will return 0 if anything is empty.

       \C'xxx'
	      Typeset character 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 avail-
	      able in compatibility mode.

       \E     This is equivalent to an escape character, but it is not interpreted in  copy-mode.
	      For example, strings to start and end superscripting could be defined like this

		     .ds { \v'-.3m'\s'\En[.s]*6u/10u'
		     .ds } \s0\v'.3m'

	      The use of \E ensures that these definitions will work even if \*{ gets interpreted
	      in copy-mode (for example, by being used in a macro argument).

       \Ff
       \F(fm
       \F[fam]
	      Change font family.  This is the same as the fam request.  \F[]  switches  back  to
	      the previous color (note that \FP won't work; it selects font family `P' instead).

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

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

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

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

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

       \On
       \O[n]  Suppressing  troff  output.   The  escapes  \02, \O3, \O4, and \O5 are intended for
	      internal use by grohtml.

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

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

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

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

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

	      \O4    End a nesting level.

	      \O5[Pfilename]
		     This escape is grohtml specific.  Provided that this escape  occurs  at  the
		     outer  nesting  level, write filename to stderr.  The position of the image,
		     P, must be specified and must be one of l, r, c, or  i  (left,  right,  cen-
		     tered, inline).  filename will be associated with the production of the next
		     inline image.

       \R'name +-n'
	      This has the same effect as

		     .nr name +-n

       \s(nn
       \s+-(nn
	      Set the point size to nn points; nn must be exactly two digits.

       \s[+-n]
       \s+-[n]
       \s'+-n'
       \s+-'n'
	      Set the point size to n scaled points; n is a numeric  expression  with  a  default
	      scale indicator of z.

       \Vx
       \V(xx
       \V[xxx]
	      Interpolate the contents of the environment variable xxx, as returned by getenv(3).
	      \V is interpreted in copy-mode.

       \Yx
       \Y(xx
       \Y[xxx]
	      This is approximately equivalent to  \X'\*[xxx]'.   However  the	contents  of  the
	      string  or macro xxx are not interpreted; also it is permitted for xxx to have been
	      defined as a macro and thus contain newlines (it is not permitted for the  argument
	      to \X to contain newlines).  The inclusion of newlines requires an extension to the
	      UNIX troff output format, and will confuse drivers that  do  not	know  about  this
	      extension.

       \Z'anything'
	      Print  anything and then restore the horizontal and vertical position; anything may
	      not contain tabs or leaders.

       \$0    The name by which the current macro was invoked.	The als request can make a  macro
	      have more than one name.

       \$*    In a macro or string, the concatenation of all the arguments separated by spaces.

       \$@    In  a  macro or string, the concatenation of all the arguments with each surrounded
	      by double quotes, and separated by spaces.

       \$(nn
       \$[nnn]
	      In a macro or string, this gives the nn-th or nnn-th argument.  Macros and  strings
	      can have an unlimited number of arguments.

       \?anything\?
	      When  used in a diversion, this will transparently embed anything in the diversion.
	      anything is read in copy mode.  When the diversion  is  reread,  anything  will  be
	      interpreted.   anything  may not contain newlines; use \! if you want to embed new-
	      lines in a diversion.  The escape sequence \? is also recognised in copy	mode  and
	      turned into a single internal code; it is this code that terminates anything.  Thus

		     .nr x 1
		     .nf
		     .di d
		     \?\\?\\\\?\\\\\\\\nx\\\\?\\?\?
		     .di
		     .nr x 2
		     .di e
		     .d
		     .di
		     .nr x 3
		     .di f
		     .e
		     .di
		     .nr x 4
		     .f

	      will print 4.

       \/     This  increases  the  width  of the preceding character so that the spacing between
	      that character and the following character will be correct if the following charac-
	      ter  is  a roman character.  It is a good idea to use this escape sequence whenever
	      an italic character is immediately followed by a roman character without any inter-
	      vening space.

       \,     This  modifies  the  spacing of the following character so that the spacing between
	      that character and the preceding character will correct if the preceding	character
	      is  a  roman  character.	 It is a good idea to use this escape sequence whenever a
	      roman character is immediately followed by an italic character without  any  inter-
	      vening space.

       \)     Like \& except that it behaves like a character declared with the cflags request to
	      be transparent for the purposes of end-of-sentence recognition.

       \~     This produces an unbreakable space that stretches like a	normal	inter-word  space
	      when a line is adjusted.

       \:     This  causes the insertion of a zero-width break point.  It is equal to \% within a
	      word but without insertion of a soft hyphen character.

       \#     Everything up to and including the next newline is ignored.  This is interpreted in
	      copy mode.  It is like \" except that \" does not ignore the terminating newline.

   New requests
       .aln xx yy
	      Create  an  alias xx for number register object named yy.  The new name and the old
	      name will be exactly equivalent.	If yy is undefined, a warning of type reg will be
	      generated, and the request will be ignored.

       .als xx yy
	      Create  an  alias xx for request, string, macro, or diversion object named yy.  The
	      new name and the old name will be exactly equivalent  (it  is  similar  to  a  hard
	      rather than a soft link).  If yy is undefined, a warning of type mac will be gener-
	      ated, and the request will be ignored.  The de, am, di, da,  ds,	and  as  requests
	      only create a new object if the name of the macro, diversion or string diversion is
	      currently undefined or if it is defined to be a request; normally they  modify  the
	      value of an existing object.

       .ami xx yy
	      Append to macro indirectly.  See the dei request below for more information.

       .am1 xx yy
	      Similar  to  .am,  but  compatibility mode is switched off during execution.  To be
	      more precise, a `compatibility save' token is inserted  at  the  beginning  of  the
	      macro  addition, and a `compatibility restore' token at the end.	As a consequence,
	      the requests am, am1, de, and de1 can be intermixed freely since the  compatibility
	      save/restore tokens only affect the macro parts defined by .am1 and .ds1.

       .asciify xx
	      This  request `unformats' the diversion xx in such a way that ASCII and space char-
	      acters (and some escape sequences) that were formatted and diverted into xx will be
	      treated like ordinary input characters when xx is reread.  Useful for diversions in
	      conjunction with the .writem request.  It can be also used  for  gross  hacks;  for
	      example, this

		     .tr @.
		     .di x
		     @nr n 1
		     .br
		     .di
		     .tr @@
		     .asciify x
		     .x

	      will  set  register n to 1.  Note that glyph information (font, font size, etc.) is
	      not preserved; use .unformat instead.

       .as1 xx yy
	      Similar to .as, but compatibility mode is switched off  during  expansion.   To  be
	      more  precise,  a  `compatibility  save'	token is inserted at the beginning of the
	      string, and a `compatibility restore' token at the  end.	 As  a	consequence,  the
	      requests	as,  as1,  ds,	and  ds1 can be intermixed freely since the compatibility
	      save/restore tokens only affect the (sub)strings defined by as1 and ds1.

       .backtrace
	      Print a backtrace of the input stack on stderr.

       .blm xx
	      Set the blank line macro to xx.  If there is a blank line macro, it will be invoked
	      when a blank line is encountered instead of the usual troff behaviour.

       .box xx
       .boxa xx
	      These requests are similar to the di and da requests with the exception that a par-
	      tially filled line will not become part  of  the	diversion  (i.e.,  the	diversion
	      always  starts with a new line) but restored after ending the diversion, discarding
	      the partially filled line which possibly comes from the diversion.

       .break Break out of a while loop.  See also the while and continue requests.  Be sure  not
	      to confuse this with the br request.

       .brp   This is the same as \p.

       .cflags n c1 c2...
	      Characters  c1, c2,... have properties determined by n, which is ORed from the fol-
	      lowing:

	      1      The character ends sentences (initially characters .?! have this property).

	      2      Lines can be broken before the character (initially no characters have  this
		     property);  a  line  will	not  be  broken at a character with this property
		     unless the characters on each side both have non-zero hyphenation codes.

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

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

	      16     The  character  overlaps vertically (initially character \(br has this prop-
		     erty).

	      32     An end-of-sentence character followed by any number of characters with  this
		     property  will  be treated as the end of a sentence if followed by a newline
		     or two spaces; in other words the character is transparent for the  purposes
		     of end-of-sentence recognition; this is the same as having a zero space fac-
		     tor in TeX (initially characters "')]*\(dg\(rq have this property).

       .char c string
	      Define character c to be string.	Every time  character  c  needs  to  be  printed,
	      string  will be processed in a temporary environment and the result will be wrapped
	      up into a single object.	Compatibility mode will be  turned  off  and  the  escape
	      character  will be set to \ while string is being processed.  Any emboldening, con-
	      stant spacing or track kerning will be applied to this object rather than to  indi-
	      vidual characters in string.

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

	      There is a special anti-recursion feature: use of character within the  character's
	      definition will be handled like normal characters not defined with char.

	      A character definition can be removed with the rchar request.

       .chop xx
	      Chop  the  last  character  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.

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

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

       .cp n  If n is non-zero or missing, enable compatibility mode, otherwise disable  it.   In
	      compatibility mode, long names are not recognised, and the incompatibilities caused
	      by long names do not arise.

       .defcolor xxx scheme color_components
	      Define color.  scheme can be one of the following values: rgb  (three  components),
	      cym  (three  components), cmyk (four components), and gray or grey (one component).
	      Color components can be given either as a hexadecimal string or as positive decimal
	      integers	in the range 0-65535.  A hexadecimal string contains all color components
	      concatenated; it must start with either # or ##.	The former specifies  hex  values
	      in  the  range  0-255  (which  are internally multiplied by 257), the latter in the
	      range 0-65535.  Examples: #FFC0CB (pink), ##ffff0000ffff (magenta).  A new  scaling
	      indicator  f has been introduced which multiplies its value by 65536; this makes it
	      convenient to specify color components as fractions in the range 0 to 1.	Example:

		     .defcolor darkgreen rgb 0.1f 0.5f 0.2f

	      Note that f is the default scaling indicator for the  defcolor  request,	thus  the
	      above statement is equivalent to

		     .defcolor darkgreen rgb 0.1 0.5 0.2

	      The  color named default (which is device-specific) can't be redefined.  It is pos-
	      sible that the default color for \M and \m is not the same.

       .dei xx yy
	      Define macro indirectly.	The following example

		     .ds xx aa
		     .ds yy bb
		     .dei xx yy

	      is equivalent to

		     .de aa bb

       .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.

       .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 pop-
	      ping of environments will be done.

       .fam xx
	      Set  the current font family to xx.  The current font family is part of the current
	      environment.  If xx is missing, switch back to previous font family.  The value  at
	      start-up	is  `T'.   See the description of the sty request for more information on
	      font families.

       .fchar c string
	      Define fallback character c to be string.  The syntax of this request is	the  same
	      as  the  char  request;  the  only difference is that a character defined with char
	      hides the glyph with the same name in the current font, whereas a character defined
	      with fchar is checked only if the particular glyph isn't found in the current font.
	      This test happens before checking special fonts.

       .fspecial f s1 s2...
	      When the current font is f, fonts s1, s2,... will be special, that  is,  they  will
	      searched	for  characters not in the current font.  Any fonts specified in the spe-
	      cial request will be searched after fonts specified in the fspecial request.

       .ftr f g
	      Translate font f to g.  Whenever a font named f is referred  to  in  an  \f  escape
	      sequence,  or  in  the ft, ul, bd, cs, tkf, special, fspecial, fp, or sty requests,
	      font g will be used.  If g is missing, or equal to f then font f will not be trans-
	      lated.

       .hcode c1 code1 c2 code2...
	      Set  the	hyphenation  code  of  character  c1 to code1 and that of c2 to code2.	A
	      hyphenation code must be a single input character (not a special	character)  other
	      than  a  digit  or a space.  Initially each lower-case letter a-z has a hyphenation
	      code, which is itself, and each upper-case letter A-Z has a hyphenation code  which
	      is the lower-case version of itself.  See also the hpf request.

       .hla lang
	      Set  the	current  hyphenation  language to lang.  Hyphenation exceptions specified
	      with the hw request and hyphenation patterns specified with  the	hpf  request  are
	      both  associated with the current hyphenation language.  The hla request is usually
	      invoked by the troffrc file.

       .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 maxi-
	      mum  associated  with  that  environment.   Hyphens  resulting from \% are counted;
	      explicit hyphens are not.

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

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

	      o      No support for `digraphs' like \$.

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

	      o      No macro expansion.

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

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

	      o      \endinput is recognized also.

	      o      For  backwards  compatibility,  if  \patterns  is missing, the whole file is
		     treated as a list of hyphenation patterns (only recognizing the %	character
		     as the start of a comment).

	      Use  the	hpfcode request to map the encoding used in hyphenation patterns files to
	      groff's input encoding.

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

       .hpfa file
	      The same as hpf except that the hyphenation patterns from file are appended to  the
	      patterns already loaded in the current language.

       .hpfcode a b c d ...
	      After reading a hyphenation patterns file with the hpf or hpfa request, convert all
	      characters with character code a in the recently read patterns to character code b,
	      character code c to d, etc.  Initially, all character codes map to themselves.  The
	      arguments of hpfcode must be integers in the range 0 to 255.  Note that it is  even
	      possible to use character codes which are invalid in groff otherwise.

       .hym n Set  the	hyphenation  margin  to n: when the current adjustment mode is not b, the
	      line will not be hyphenated if the line is no  more  than  n  short.   The  default
	      hyphenation margin is 0.	The default scaling indicator for this request is m.  The
	      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 hyphen-
	      ate 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 indica-
	      tor for this request is m.  The hyphenation space is associated  with  the  current
	      environment.  The current hyphenation space is available in the \n[.hys] register.

       .itc n macro
	      Variant of .it for which a line interrupted with \c counts as one input line.

       .kern n
	      If n is non-zero or missing, enable pairwise kerning, otherwise disable it.

       .length xx string
	      Compute  the length of string and return it in the number register xx (which is not
	      necessarily defined before).

       .linetabs n
	      If n is non-zero or missing, enable line-tabs mode, otherwise disable it (which  is
	      the  default).  In line-tabs mode, tab distances are computed relative to the (cur-
	      rent) output line.  Otherwise they are taken relative to the input line.	For exam-
	      ple, the following

		     .ds x a\t\c
		     .ds y b\t\c
		     .ds z c
		     .ta 1i 3i
		     \*x
		     \*y
		     \*z

	      yields

		     a	       b	 c

	      In line-tabs mode, the same code gives

		     a	       b		   c

	      Line-tabs  mode  is  associated  with the current environment; the read-only number
	      register \n[.linetabs] is set to 1 if in line-tabs mode, and 0 otherwise.

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

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

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

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

       .opena stream filename
	      Like open, but if filename exists, append to it instead of truncating it.

       .output string
	      Emit  string  directly to the intermediate output (subject to copy-mode interpreta-
	      tion); this is similar to \!  used at the top level.  An initial	double	quote  in
	      string is stripped off to allow initial blanks.

       .pnr   Print the names and contents of all currently defined number registers on stderr.

       .psbb filename
	      Get  the	bounding  box  of a PostScript image filename.	This file must conform to
	      Adobe's Document Structuring Conventions; the command  looks  for  a  %%BoundingBox
	      comment  to  extract the bounding box values.  After a successful call, the coordi-
	      nates (in PostScript units) of the lower left and upper right corner can	be  found
	      in  the  registers  \n[llx],  \n[lly], \n[urx], and \n[ury], respectively.  If some
	      error has occurred, the four registers are set to zero.

       .pso command
	      This behaves like the so request except that input comes from the  standard  output
	      of command.

       .ptr   Print  the  names  and  positions  of all traps (not including input line traps and
	      diversion traps) on stderr.  Empty slots in the page trap list are printed as well,
	      because they can affect the priority of subsequently planted traps.

       .pvs +-n
	      Set  the	post-vertical  line space to n; default scale indicator is p.  This value
	      will be added to each line after it has been output.  With no argument,  the  post-
	      vertical line space is set to its previous value.

	      The total vertical line spacing consists of four components: .vs and \x with a neg-
	      ative 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 characters c1, c2,...  This undoes the effect of a char
	      request.

       .return
	      Within a macro, return immediately.  No effect otherwise.

       .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.

       .shc c Set the soft hyphen character to c.  If c is omitted,  the  soft	hyphen	character
	      will  be set to the default \(hy.  The soft hyphen character is the character which
	      will be inserted when a word is hyphenated at a line break.   If	the  soft  hyphen
	      character  does  not  exist  in  the  font of the character immediately preceding a
	      potential break point, then the line will not be broken  at  that  point.   Neither
	      definitions  (specified with the char request) nor translations (specified with the
	      tr request) are considered when finding the soft hyphen character.

       .shift n
	      In a macro, shift the arguments by n positions: argument i  becomes  argument  i-n;
	      arguments  1  to n will no longer be available.  If n is missing, arguments will be
	      shifted by 1.  Shifting by negative amounts is currently undefined.

       .sizes s1 s2...sn [0]
	      This command is similar to the sizes command of a DESC file.  It sets the available
	      font sizes for the current font to s1, s2,..., sn scaled points.	The list of sizes
	      can be terminated by an optional 0.  Each si can also be	a  range  of  sizes  m-n.
	      Contrary	to  the  font file command, the list can't extend over more than a single
	      line.

       .special s1 s2...
	      Fonts s1, s2, are special and will be searched for characters not  in  the  current
	      font.

       .spreadwarn limit
	      Make  troff  emit a warning if the additional space inserted for each space between
	      words in an output line is larger or equal to limit.  A negative value  is  changed
	      to  zero;  no  argument toggles the warning on and off without changing limit.  The
	      default scaling indicator is m.  At startup, spreadwarn is deactivated,  and  limit
	      is set to 3m.  For example, .spreadwarn 0.2m will cause a warning if troff must add
	      0.2m or more for each interword space in a line.	This request is  active  only  if
	      text is justified to both margins (using .ad b).

       .sty n f
	      Associate  style	f with font position n.  A font position can be associated either
	      with a font or with a style.  The current font is the index of a font position  and
	      so is also either a font or a style.  When it is a style, the font that is actually
	      used is the font the name of which is the concatenation of the name of the  current
	      family  and  the	name of the current style.  For example, if the current font is 1
	      and font position 1 is associated with style R and the current font  family  is  T,
	      then  font  TR  will be used.  If the current font is not a style, then the current
	      family is ignored.  When the requests cs, bd, tkf, uf, or fspecial are applied to a
	      style, then they will instead be applied to the member of the current family corre-
	      sponding to that style.  The default family can be set with  the	-f  option.   The
	      styles  command  in  the	DESC file controls which font positions (if any) are ini-
	      tially associated with styles rather than fonts.

       .substring xx n1 [n2]
	      Replace the string named xx with the substring defined by the indices  n1  and  n2.
	      The first character in the string has index 0.  If n2 is omitted, it is taken to be
	      equal to the string's length.  If the index value n1 or n2 is negative, it will  be
	      counted  from  the  end  of  the	string,  going	backwards: The last character has
	      index -1, the character before the last 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
	      character  will be increased by an amount between n1 and n2; when the current point
	      size is less than or equal to s1 the width will be increased  by	n1;  when  it  is
	      greater  than or equal to s2 the width will be increased by n2; when the point size
	      is greater than or equal to s1 and less than or equal to s2 the increase	in  width
	      is a linear function of the point size.

       .tm1 string
	      Similar  to the tm request, string is read in copy mode and written on the standard
	      error, but an initial double quote in string  is	stripped  off  to  allow  initial
	      blanks.

       .tmc string
	      Similar to tm1 but without writing a final newline.

       .trf filename
	      Transparently output the contents of file filename.  Each line is output as if pre-
	      ceded by \!; however, the lines are not subject to  copy-mode  interpretation.   If
	      the  file  does not end with a newline, then a newline will be added.  For example,
	      you can define a macro x containing the contents of file f, using

		     .di x
		     .trf f
		     .di

	      Unlike with the cf request, the file cannot contain characters such as NUL that are
	      not legal troff input characters.

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

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

       .troff Make  the  n  built-in  condition  false,  and the t built-in condition true.  This
	      undoes the effect of the nroff request.

       .unformat xx
	      This request `unformats' the diversion xx.  Contrary to the .asciify request, which
	      tries  to  convert formatted elements of the diversion back to input tokens as much
	      as possible, .unformat will only handle 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 verti-
	      cal  size  of  lines  is	not preserved.	Glyph information (font, font size, space
	      width, etc.) is retained.  Useful in conjunction with the .box and .boxa requests.

       .vpt n Enable vertical position traps if n is non-zero, disable them otherwise.	 Vertical
	      position traps are traps set by the wh or dt requests.  Traps set by the it request
	      are not vertical position traps.	The  parameter	that  controls	whether  vertical
	      position	traps  are  enabled  is  global.   Initially  vertical position traps are
	      enabled.

       .warn n
	      Control warnings.  n is the sum of the numbers associated with each warning that is
	      to  be  enabled;	all  other warnings will be disabled.  The number associated with
	      each warning is listed in troff(1).  For example, .warn 0 will  disable  all  warn-
	      ings,  and  .warn 1 will disable all warnings except that about missing characters.
	      If n is not given, all warnings will be enabled.

       .warnscale si
	      Set the scaling indicator used in warnings to si.  Valid values for si are u, i, c,
	      p, and P.  At startup, it is set to i.

       .while c anything
	      While condition c is true, accept anything as input; c can be any condition accept-
	      able to an if request; anything can comprise  multiple  lines  if  the  first  line
	      starts  with  \{	and  the last line ends with \}.  See also the break and continue
	      requests.

       .write stream anything
	      Write anything to the stream named stream.  stream must previously  have	been  the
	      subject  of  an  open  request.  anything is read in copy mode; a leading " will be
	      stripped.

       .writec stream anything
	      Similar to write but without writing a final newline.

       .writem stream xx
	      Write the contents of the macro or string xx to the stream  named  stream.   stream
	      must previously have been the subject of an open request.  xx is read in copy mode.

   Extended requests
       .cf filename
	      When  used  in  a diversion, this will embed in the diversion an object which, when
	      reread, will cause the contents of filename to be transparently copied  through  to
	      the  output.  In UNIX troff, the contents of filename is immediately copied through
	      to the output regardless of whether there is a current diversion; this behaviour is
	      so anomalous that it must be considered a bug.

       .ev xx If  xx  is  not  a  number, this will switch to a named environment called xx.  The
	      environment should be popped with a matching ev request without any arguments, just
	      as  for  numbered  environments.	There is no limit on the number of named environ-
	      ments; they will be created the first time that they are referenced.

       .ss m n
	      When two arguments are given to the ss request, the second argument gives the  sen-
	      tence  space  size.   If	the second argument is not given, the sentence space size
	      will be the same as the word space size.	Like the word space  size,  the  sentence
	      space  is in units of one twelfth of the spacewidth parameter for the current font.
	      Initially both the word space size and the sentence space size are 12.  Contrary to
	      UNIX  troff,  GNU  troff	handles this request in nroff mode also; a given value is
	      then rounded down to the nearest multiple of 12.	The sentence space size  is  used
	      in two circumstances.  If the end of a sentence occurs at the end of a line in fill
	      mode, then both an inter-word space and a sentence space will be added; if two spa-
	      ces  follow  the	end  of a sentence in the middle of a line, then the second space
	      will be a sentence space.  Note that the behaviour of UNIX troff	will  be  exactly
	      that  exhibited by GNU troff if a second argument is never given to the ss request.
	      In GNU troff, as in UNIX troff, you should always follow a sentence with	either	a
	      newline or two spaces.

       .ta n1 n2...nn T r1 r2...rn
	      Set  tabs  at positions n1, n2,..., nn and then set tabs at nn+r1, nn+r2,..., nn+rn
	      and then at nn+rn+r1, nn+rn+r2,..., nn+rn+rn, and so on.	For example,

		     .ta T .5i

	      will set tabs every half an inch.

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

       \n[.C] 1 if compatibility mode is in effect, 0 otherwise.

       \n[.cdp]
	      The depth of the last character added to the current environment.  It  is  positive
	      if the character 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 character added to the current environment.  It is positive
	      if the character extends above the baseline.

       \n[.color]
	      1 if colors are enabled, 0 otherwise.

       \n[.csk]
	      The skew of the last character added to the current environment.	 The  skew  of	a
	      character  is  how  far  to the right of the center of a character the center of an
	      accent over that character 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[.hla]
	      The current hyphenation language as set by the hla request.

       \n[.hlc]
	      The number of immediately preceding consecutive hyphenated lines.

       \n[.hlm]
	      The  maximum  allowed  number  of  consecutive  hyphenated lines, as set by the hlm
	      request.

       \n[.hy]
	      The current hyphenation flags (as set by the hy request).

       \n[.hym]
	      The current hyphenation margin (as set by the hym request).

       \n[.hys]
	      The current hyphenation space (as set by the hys request).

       \n[.in]
	      The indent that applies to the current output line.

       \n[.int]
	      Set to a positive value if last output line is interrupted (i.e.,  if  it  contains
	      \c).

       \n[.kern]
	      1 if pairwise kerning is enabled, 0 otherwise.

       \n[.lg]
	      The current ligature mode (as set by the lg request).

       \n[.linetabs]
	      The current line-tabs mode (as set by the linetabs request).

       \n[.ll]
	      The line length that applies to the current output line.

       \n[.lt]
	      The title length as set by the lt request.

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

       \n[.ps]
	      The current pointsize in scaled points.

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

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

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

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

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

       \n[.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  posi-
	      tion 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  con-
	      junction with the \n[.ne] register.

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

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

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

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

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

       \n[llx]
       \n[lly]
       \n[urx]
       \n[ury]
	      These four registers are set by the .psbb request and contain the bounding box val-
	      ues (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 charac-
	      ters.

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

       \n[skw]
	      How far to right of the center of the last character in the \w argument, the center
	      of an accent from a roman font should be placed over that character.

       Other available read/write number registers are:

       \n[c.] The current input line number.  \n[.c] is a read-only alias to this register.

       \n[hours]
	      The number of hours past midnight.  Initialized at start-up.

       \n[hp] The current horizontal position at input line.

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

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

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

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

       \n[year]
	      The current year.  Note that the traditional troff number register  \n[yr]  is  the
	      current year minus 1900.

   Miscellaneous
       troff  predefines  a  single (read/write) string-based register, \*(.T, which contains the
       argument given to the -T command line option, namely the current output device (for  exam-
       ple,  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 posi-
       tion, which can be found in the \n[.fp] register; although troff  does  not  enforce  this
       strictly,  it  will  not  allow	a  font  to be mounted at a position whose number is much
       greater than that of any currently used position.

       Interpolating a string does not hide existing macro arguments.  Thus in a  macro,  a  more
       efficient way of doing

	      .xx \\$@

       is

	      \\*[xx]\\

       If  the	font description file contains pairwise kerning information, characters from that
       font will be kerned.  Kerning between two characters can be  inhibited  by  placing  a  \&
       between them.

       In a string comparison in a condition, characters that appear at different input levels to
       the first delimiter character will not be recognised as the second  or  third  delimiters.
       This applies also to the tl request.  In a \w escape sequence, a character that appears at
       a different input level to the starting delimiter character will not be recognised as  the
       closing delimiter character.  The same is true for \A, \b, \B, \C, \l, \L, \o, \X, and \Z.
       When decoding a macro or string argument that is delimited by double quotes,  a	character
       that  appears  at  a different input level to the starting delimiter character will not be
       recognised as the closing delimiter character.  The implementation of \$@ ensures that the
       double quotes surrounding an argument will appear the same input level, which will be dif-
       ferent to the input level of the argument itself.  In a long escape name  ]  will  not  be
       recognized  as  a  closing  delimiter except when it occurs at the same input level as the
       opening ].  In compatibility mode, no attention is paid to the input-level.

       There are some new types of condition:

       .if rxxx
	      True if there is a number register named xxx.

       .if dxxx
	      True if there is a string, macro, diversion, or request named xxx.

       .if mxxx
	      True if there is a color named xxx.

       .if cch
	      True if there is a character ch available; ch is either an  ASCII  character  or	a
	      special  character  \(xx	or \[xxx]; the condition will also be true if ch has been
	      defined by the char request.

       The tr request can now map characters onto \~.

       It is now possible to have whitespace between the first and second dot (or the name of the
       ending macro) to end a macro definition.  Example:

	      .de foo
	      . nop Hello, I'm `foo'.
	      . nop I will now define `bar'.
	      . de bar
	      . nop Hello, I'm `bar'.
	      . .
	      . nop Done.
	      ..
	      .foo
	      .bar

INTERMEDIATE OUTPUT FORMAT
       This  section  describes  the  format  output by GNU troff.  The output format used by GNU
       troff is very similar to that used by Unix device-independent troff.  Only the differences
       are documented here.

   Units
       The argument to the s command is in scaled points (units of points/n, where n is the argu-
       ment to the sizescale command  in the DESC file).  The argument to the x Height command is
       also in scaled points.

   Text Commands
       Nn     Print character with index n (a non-negative integer) of the current font.

       If  the	tcommand  line is present in the DESC file, troff will use the following two com-
       mands.

       txxx   xxx is any sequence of characters terminated by a space or  a  newline;  the  first
	      character  should  be printed at the current position, the current horizontal posi-
	      tion should be increased by the width of the first character, and so  on	for  each
	      character.   The	width  of the character is that given in the font file, appropri-
	      ately 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 com-
	      mand.

       un xxx This is same as the t command except that after printing each character,	the  cur-
	      rent 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  characters and fonts can be of arbitrary length; drivers should not assume
       that they will be only two characters long.

       When a character is to be printed, that character will always  be  in  the  current  font.
       Unlike  device-independent  troff, it is not necessary for drivers to search special fonts
       to find a character.

       For color support, some new commands have been added:

       mc cyan magenta yellow
       md
       mg gray
       mk cyan magenta yellow black
       mr red green blue
	      Set the color components of the current drawing color, using various color schemes.
	      md  resets  the  drawing color to the default value.  The arguments are integers in
	      the range 0 to 65536.

       The x device control command has been extended.

       x u n  If n is 1, start underlining of spaces.  If n is 0,  stop  underlining  of  spaces.
	      This is needed for the cu request in nroff mode and is ignored otherwise.

   Drawing Commands
       The  D drawing command has been extended.  These extensions will not be used by GNU pic if
       the -n option is given.

       Df n\n Set the shade of gray to be used for filling solid objects to n; n must be an inte-
	      ger  between  0  and 1000, where 0 corresponds solid white and 1000 to solid black,
	      and values in between correspond to intermediate shades of gray.	This applies only
	      to  solid  circles, solid ellipses and solid polygons.  By default, a level of 1000
	      will be used.  Whatever color a solid object  has,  it  should  completely  obscure
	      everything  beneath it.  A value greater than 1000 or less than 0 can also be used:
	      this means fill with the shade of gray that is currently being used for  lines  and
	      text.   Normally this will be black, but some drivers may provide a way of changing
	      this.

       DC d\n Draw a solid circle with a diameter of d with the leftmost  point  at  the  current
	      position.

       DE dx dy\n
	      Draw a solid ellipse with a horizontal diameter of dx and a vertical diameter of dy
	      with the leftmost point at the current position.

       Dp dx1 dy1 dx2 dy2 ... dxn dyn\n
	      Di_1 a polygon with, for i=1,...,n+1, the  i-th  vertex  at  the	current  position
	      + > (dxj,dyj).  At the moment, GNU pic only uses this command to generate triangles
	       j=1
	      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.  Traditionally Unix troff  driv-
	      ers  use	a  line  thickness proportional to the current point size; drivers should
	      continue to do this if no Dt command has been given, or if a Dt  command	has  been
	      given with a negative value of n.  A zero value of n selects the smallest available
	      line thickness.

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

	      \D'c x1 y1 x2 y2 ... xn yn'

       where c is not one of c, e, l, a, or ~, Unix troff will treat each of the xi as a horizon-
       tal  quantity, and ea_h of the yi as a vertical qua_tity and will assume that the width of
       the drawn object is  > xi, and that the height is  > yi.  (The assumption about the height
			   i=1				 i=1
       can  be	seen  by  examining  the st and sb registers after using such a D command in a \w
       escape sequence).  This rule also holds for all the original  drawing  commands	with  the
       exception  of  De.   For  the sake of compatibility GNU troff also follows this rule, even
       though it produces an ugly result in the case of the Dt, and, to a lesser extent, DE  com-
       mands.  Thus after executing a D command of the form

	      Dc x1 y1 x2 y2 ... xn yn\n
						     _	   _
       the current position should be increased by ( > xi, > yi).
						    i=1   i=1

       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.

       Note  that  Df is now mapped onto DFg.  The current position isn't changed by those colour
       commands.

   Device Control Commands
       There is a continuation convention which permits the argument to the x X command  to  con-
       tain newlines: when outputting the argument to the x X command, GNU troff will follow each
       newline in the argument with a + character (as usual, it will terminate the  entire  argu-
       ment  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 compati-
       bility 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
       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  oth-
       erwise.

       This  became  necessary	because the GNU concept for long names causes some incompatibili-
       ties.  Classical troff interprets

	      .dsabcd

       as defining a string ab with contents cd.  In groff mode, this will  be	considered  as	a
       call of a macro named dsabcd.

       Also  classical	troff  interprets \*[ or \n[ as references to a string or number register
       called [ while groff takes this as the start of a long name.

       In compatibility mode, groff interprets these things in the traditional way; so long names
       are not recognized.

       On  the	other  hand,  groff in GNU native mode does not allow to use the single-character
       escapes \\ (backslash), \| (vertical bar), \^ (caret), \& (ampersand), \{ (opening brace),
       \}  (closing  brace),  '\ '  (space),  \'  (single  quote), \` (backquote), \- (minus), \_
       (underline), \! (bang), \% (percent), and \c (character c) in names  of	strings,  macros,
       diversions, number registers, fonts or environments, whereas classical troff does.

       The \A escape sequence can be helpful in avoiding these escape sequences in names.

       Fractional  pointsizes  cause  one noteworthy incompatibility.  In classical troff, the ps
       request ignores scale indicators and so

	      .ps 10u

       will set the pointsize to 10 points, whereas in groff native mode the  pointsize  will  be
       set to 10 scaled points.

       In groff mode, there is a fundamental difference between unformatted input characters, and
       formatted output characters.  Everything that affects how an output character will be out-
       put  is	stored	with  the  character; once an output character has been constructed it is
       unaffected by any subsequent requests that are executed, including the bd, cs, tkf, tr, or
       fp requests.

       Normally output characters are constructed from input characters at the moment immediately
       before the character 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 out-
       put characters in any combination.

       An output character does not behave like an input character for the purposes of macro pro-
       cessing;  it  does not inherit any of the special properties that the input character from
       which it was constructed might have had.  The following example will make things clearer.

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

       In GNU mode this will be printed as \\.	So each pair of input backslashes '\\' is  turned
       into  a	single	output	backslash '\' and the resulting output backslashes are not inter-
       preted as escape characters when they are reread.

       Classical troff would interpret them as escape characters when they were reread and  would
       end up printing a single backslash '\'.

       In  GNU,  the correct way to get a printable version of the backslash character '\' is the
       \(rs escape sequence, but classical troff does not provide a clean feature for  getting	a
       non-syntactical	backslash.  A close method is the printable version of the current escape
       character using the \e escape sequence; this works if the current escape character is  not
       redefined.   It	works  in  both  GNU mode and compatibility mode, while dirty tricks like
       specifying a sequence of multiple backslashes do not work reliably; for the different han-
       dling  in  diversions,  macro definitions, or text mode quickly leads to a confusion about
       the necessary number of backslashes.

       To store an escape sequence in a diversion that will be interpreted when the diversion  is
       reread,	either	the  traditional  \!  transparent  output  facility  or the new \? escape
       sequence can be used.

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

       o The positioning after the drawing of the polygons conflicts with the  classical  defini-
	 tion.

       o The  intermediate  output cannot be rescaled to other devices as classical "device-inde-
	 pendent" troff did.

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

       This document is distributed under the terms of the FDL (GNU Free  Documentation  License)
       version	1.1  or  later.  You should have received a copy of the FDL on your system, it is
       also available on-line at the GNU  copyleft  site  <http://www.gnu.org/copyleft/fdl.html>.
       This   document	was  written  by  James  Clark,  with  modifications  by  Werner  Lemberg
       <wl@gnu.org> and Bernd Warken <bwarken@mayn.de>.

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

SEE ALSO
       The  groff  info  file, cf. info(1) presents all groff documentation within a single docu-
       ment.

       groff(1)
	      A list of all documentation around groff.

       groff(7)
	      A description of the groff language, including a short, but complete  reference  of
	      all  predefined  requests, registers, and escapes of plain groff.  From the command
	      line, this is called using

	      shell# man 7 groff

       roff(7)
	      A survey of roff systems, including pointers to further historical documentation.

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

Groff Version 1.18.1			   05 July 2002 			    GROFF_DIFF(7)


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