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@G@TROFF(1)							   @G@TROFF(1)

NAME
       @g@troff - format documents

SYNOPSIS
       @g@troff [ -abivzCER ] [ -wname ] [ -Wname ] [ -dcs ] [ -ffam ]
		[ -mname ] [ -nnum ] [ -olist ] [ -rcn ] [ -Tname ] [ -Fdir ]
		[ -Mdir ] [ files... ]

DESCRIPTION
       This  manual  page describes the GNU version of troff, which is part of
       the groff document formatting system.  It  is  highly  compatible  with
       Unix  troff.   Usually  it  should  be invoked using the groff command,
       which will also run preprocessors and postprocessors in the appropriate
       order and with the appropriate options.

OPTIONS
       -a	 Generate an ASCII approximation of the typeset output.

       -b	 Print	a  backtrace with each warning or error message.  This
		 backtrace should help track down the cause of the error.  The
		 line  numbers	given  in the backtrace may not always be cor‐
		 rect: troff's idea of line numbers gets confused by as or  am
		 requests.

       -i	 Read  the standard input after all the named input files have
		 been processed.

       -v	 Print the version number.

       -wname	 Enable warning name.  Available warnings are described in the
		 Warnings subsection below.  Multiple -w options are allowed.

       -Wname	 Inhibit warning name.	Multiple -W options are allowed.

       -E	 Inhibit all error messages.

       -z	 Suppress formatted output.

       -C	 Enable compatibility mode.

       -dcs
       -dname=s	 Define	 c  or	name  to be a string s; c must be a one letter
		 name.

       -ffam	 Use fam as the default font family.

       -mname	 Read in the file tmac.name.  Normally this will  be  searched
		 for in @MACRODIR@.

       -R	 Don't load troffrc.

       -nnum	 Number the first page num.

       -olist	 Output only pages in list, which is a comma-separated list of
		 page ranges; n means print page n, m-n means print every page
		 between  m and n, -n means print every page up to n, n- means
		 print every page from n.

       -rcn
       -rname=n	 Set number register c or name to n; c must be a one character
		 name; n can be any troff numeric expression.

       -Tname	 Prepare  output  for  device  name,  rather  than the default
		 @DEVICE@.

       -Fdir	 Search dir for subdirectories devname (name is	 the  name  of
		 the  device) for the DESC file and font files before the nor‐
		 mal @FONTDIR@.

       -Mdir	 Search directory  dir	for  macro  files  before  the	normal
		 @MACRODIR@.

USAGE
       Only the features not in Unix troff are described here.

   Long names
       The  names  of number registers, fonts, strings/macros/diversions, spe‐
       cial characters can be of any length. In escape	sequences,  where  you
       can  use	 (xx for a two character name, you can use [xxx] for a name of
       arbitrary length:

       \[xxx] Print the special character called xxx.

       \f[xxx]
	      Set font xxx.

       \*[xxx]
	      Interpolate string xxx.

       \n[xxx]
	      Interpolate number register xxx.

   Fractional pointsizes
       A scaled point is equal to 1/sizescale points, where sizescale is spec‐
       ified  in the DESC file (1 by default.)	There is a new scale indicator
       z which 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 will be
       equivalent to a millipoint; the request .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 a  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.  Similarily 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 a 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.

       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  according  as anything is or is not
	      acceptable as the name of a  string,  macro,  diversion,	number
	      register,	 environment or font.  It will return 0 if anything is
	      empty.  This is useful if you want to lookup user input in  some
	      sort of associative table.

       \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 available in compatibility mode.

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

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

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

       \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 char‐
	      acter with that code, special fonts will not be  searched.   The
	      \N  escape sequence can be conveniently used on conjunction with
	      the char request:

		     .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.

       \R'name ±n'
	      This has the same effect as

		     .nr name ±n

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

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

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

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

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

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

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

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

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

       \?anything\?
	      When used in a diversion, this will transparently embed anything
	      in the diversion.	 anything is read  in  copy  mode.   When  the
	      diversion is reread, anything will be interpreted.  anything may
	      not contain newlines; use \!  if you want to embed newlines in a
	      diversion.   The	escape sequence \?  is also recognised in copy
	      mode and turned into a single internal code;  it	is  this  code
	      that terminates anything.	 Thus
		     .nr x 1
		     .nf
		     .di d
		     \?\\?\\\\?\\\\\\\\nx\\\\?\\?\?
		     .di
		     .nr x 2
		     .di e
		     .d
		     .di
		     .nr x 3
		     .di f
		     .e
		     .di
		     .nr x 4
		     .f

	      will print 4.

       \/     This  increases the width of the preceding character so that the
	      spacing between that character and the following character  will
	      be correct if the following character is a roman character.  For
	      example, if an italic f is immediately followed by a roman right
	      parenthesis,  then  in many fonts the top right portion of the f
	      will overlap the top left of the right parenthesis producing f),
	      which  is	 ugly.	Inserting \/ produces f) and avoids this prob‐
	      lem.  It is a good idea to use this escape sequence whenever  an
	      italic  character	 is  immediately followed by a roman character
	      without any intervening 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.   For
	      example,	inserting \, between the parenthesis and the f changes
	      (f to (f.	 It is a good idea to use this escape  sequence	 when‐
	      ever  a  roman  character	 is  immediately followed by an italic
	      character 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.

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

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

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

       .asciify xx
	      This request only exists in order to make it  possible  to  make
	      certain  gross  hacks  work  with GNU troff.  It `unformats' the
	      diversion xx in such a way that ASCII characters that were  for‐
	      matted  and diverted into xx will be treated like ordinary input
	      characters when xx is reread.  For example, this

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

	      will set register n to 1.

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

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

       .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);

	      4	     lines can be broken after the character (initially	 char‐
		     acters -\(hy\(em have this property);

	      8	     the character overlaps horizontally (initially characters
		     \(ul\(rn\(ru have this property);

	      16     the character overlaps  vertically	 (initially  character
		     \(br has this property);

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

       .char c string
	      Define  character	 c to be string.  Every time character c needs
	      to be printed, string will be processed in a temporary  environ‐
	      ment  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 embolden‐
	      ing, constant spacing or track kerning will be applied  to  this
	      object  rather than to individual characters in string.  A char‐
	      acter defined by this request can be used	 just  like  a	normal
	      character	 provided  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 pat‐
	      terns can be drawn with the character using the \l and \L escape
	      sequences; words containing the character can be hyphenated cor‐
	      rectly, if the hcode request is used to  give  the  character  a
	      hyphenation  code.   There  is a special anti-recursion feature:
	      use of character within the character's definition will be  han‐
	      dled  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 diver‐
	      sions 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.

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

       .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.

       .fam xx
	      Set  the	current font family to xx.  The current font family is
	      part of the current environment.	See the description of the sty
	      request for more information on font families.

       .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  special  request will be
	      searched before fonts specified in the fspecial request.

       .ftr f g
	      Translate font f to g.  Whenever a font named f is  referred  to
	      in  \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 translated.

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

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

       .hlm n Set the maximum number of consecutive hyphenated lines to n.  If
	      n	 is  negative,	there is no maximum.  The default value is -1.
	      This value is associated with  the  current  environment.	  Only
	      lines output from an environment count towards the maximum asso‐
	      ciated with that environment.  Hyphens  resulting	 from  \%  are
	      counted; explicit hyphens are not.

       .hpf file
	      Read  hyphenation	 patterns from file; this will be searched for
	      in the same way that tmac.name is searched for when  the	-mname
	      option  is  specified.   It  should  have the same format as the
	      argument to the \patterns primitive in TeX; the letters  appear‐
	      ing  in  this  file  are	interpreted as hyphenation codes.  A %
	      character in the patterns file introduces a comment that contin‐
	      ues  to the end of the line.  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.

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

       .hys n Set the hyphenation space to n: when the current adjustment mode
	      is b don't hyphenate the line if the line can  be	 justified  by
	      adding  no  more	than  n	 extra	space to each word space.  The
	      default hyphenation space is 0.  The default  scaling  indicator
	      for this request is m.  The hyphenation space is associated with
	      the current  environment.	  The  current	hyphenation  space  is
	      available in the \n[.hys] register.

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

       .mso file
	      The same as the so request except that file is searched  for  in
	      the  same	 way  that  tmac.name  is searched for when the -mname
	      option is specified.

       .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.

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

       .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.

       .rchar c1 c2...
	      Remove the definitions of characters c1, c2,...  This undoes the
	      effect of a char 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
	      justifed 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  charac‐
	      ter does not exist in the font of the character immediately pre‐
	      ceding a potential break point, then the line will not be broken
	      at  that	point.	 Neither  definitions (specified with the char
	      request) nor translations (specified with the  tr	 request)  are
	      considered when finding the soft hyphen character.

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

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

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

       .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.

       .trf filename
	      Transparently  output  the contents of file filename.  Each line
	      is output as it would be were it preceded 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.

       .trnt abcd
	      This  is the same as the tr request except that the translations
	      do not apply to text that is  transparently  throughput  into  a
	      diversion with \!.  For example,

	      .tr ab
	      .di x
	      \!.tm a
	      .di
	      .x

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

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

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

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

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

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

   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 behavior 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 environ‐
	      ments.  There is no limit on the number of  named	 environments;
	      they will be created the first time that they are referenced.

       .fp n f1 f2
	      The  fp  request	has an optional third argument.	 This argument
	      gives the external name of the font, which is used  for  finding
	      the font description file.  The second argument gives the inter‐
	      nal name of the font which is used to refer to the font in troff
	      after  it	 has been mounted.  If there is no third argument then
	      the internal name will be used as the external name.  This  fea‐
	      ture  allows  you	 to use fonts with long names in compatibility
	      mode.

       .ss m n
	      When two arguments are given to the ss request, the second argu‐
	      ment  gives  the sentence space size.  If the second argument is
	      not given, the sentence space size will be the same as the  word
	      space  size.  Like the word space size, the sentence space is in
	      units of one twelfth of the spacewidth parameter for the current
	      font.  Initially both the word space size and the sentence space
	      size are 12.  The sentence space size is	used  in  two  circum‐
	      stances: if the end of a sentence occurs at the end of a line in
	      fill mode, then both an inter-word space and  a  sentence	 space
	      will be added; if two spaces follow the end of a sentence in the
	      middle of a line, then the  second  space	 will  be  a  sentence
	      space.   Note  that  the behaviour of Unix troff will be exactly
	      that exhibited by GNU troff if a second argument is never	 given
	      to  the  ss request.  In GNU troff, as in Unix troff, you should
	      always follow a sentence with either a newline or two spaces.

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

		     .ta T .5i

	      will set tabs every half an inch.

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

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

       \n[.cdp]
	      The depth of the last character added to	the  current  environ‐
	      ment.   It  is positive if the character extends below the base‐
	      line.

       \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 environ‐
	      ment.  It is positive if the character extends above  the	 base‐
	      line.

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

       \n[.lg]
	      The current ligature mode (as set by the lg 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[.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[.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[.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[.ss]
       \n[.sss]
	      These give the values of the parameters set  by  the  first  and
	      second arguments of the ss request.

       \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 the `Warnings' subsection.

       \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.

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

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

       \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.

       The following read/write number registers are available:

       \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.

   Miscellaneous
       Fonts not listed in the DESC file are automatically mounted on the next
       available font position when they are referenced.  If a font is	to  be
       mounted	explicitly  with the fp request on an unused font position, it
       should be mounted on the first unused font position, which can be found
       in the \n[.fp] register; although troff does not enforce this strictly,
       it will not allow a font to be mounted at a position  whose  number  is
       much greater than that of any currently used position.

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

	      .xx \\$@

       is

	      \\*[xx]\\

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

       In a string comparison in a condition, characters that appear  at  dif‐
       ferent input levels to the first delimiter character will not be recog‐
       nized as the second or third delimiters.	 This applies also to  the  tl
       request.	  In  a \w escape sequence, a character that appears at a dif‐
       ferent input level to the starting  delimiter  character	 will  not  be
       recognised  as  the closing delimiter character.	 When decoding a macro
       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 at the same input level, which will be different	to  the	 input
       level of the argument itself.  In a long escape name ] will not be rec‐
       ognized as a closing delimiter except when it occurs at the same	 input
       level as the opening ].	In compatibility mode, no attention is paid to
       the input-level.

       There are some new types of condition:

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

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

       .if 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.

   Warnings
       The  warnings that can be given by troff are divided into the following
       categories.  The name associated with each warning is used  by  the  -w
       and  -W	options;  the  number  is used by the warn request, and by the
       .warn register.

       char	      1	  Non-existent	characters.   This   is	  enabled   by
			  default.

       number	      2	  Invalid  numeric  expressions.   This	 is enabled by
			  default.

       break	      4	  In fill mode, lines which could  not	be  broken  so
			  that	their  length  was  less than the line length.
			  This is enabled by default.

       delim	      8	  Missing or mismatched closing delimiters.

       el	     16	  Use of the el request with no matching ie request.

       scale	     32	  Meaningless scaling indicators.

       range	     64	  Out of range arguments.

       syntax	    128	  Dubious syntax in numeric expressions.

       di	    256	  Use of di or da without an argument when there is no
			  current diversion.

       mac	    512	  Use  of  undefined  strings,	macros and diversions.
			  When an undefined  string,  macro  or	 diversion  is
			  used, that string is automatically defined as empty.
			  So, in most cases, at most one warning will be given
			  for each name.

       reg	   1024	  Use  of  undefined  number registers.	 When an unde‐
			  fined number register	 is  used,  that  register  is
			  automatically defined to have a value of 0.  a defi‐
			  nition is automatically made with a value of 0.  So,
			  in most cases, at most one warning will be given for
			  use of a particular name.

       tab	   2048	  Use of a tab character where a number was expected.

       right-brace 4096	  Use of \} where a number was expected.

       missing	   8192	  Requests that are missing non-optional arguments.

       input	  16384	  Illegal input characters.

       escape	  32768	  Unrecognized escape sequences.  When an unrecognized
			  escape sequence is encountered, the escape character
			  is ignored.

       space	  65536	  Missing space between a request  or  macro  and  its
			  argument.   This warning will be given when an unde‐
			  fined name longer than  two  characters  is  encoun‐
			  tered, and the first two characters of the name make
			  a defined name.  The request or macro	 will  not  be
			  invoked.   When  this	 warning is given, no macro is
			  automatically defined.  This is enabled by  default.
			  This warning will never occur in compatibility mode.

       font	 131072	  Non-existent fonts.  This is enabled by default.

       There are also names that can be used to refer to groups of warnings:

       all    All  warnings  except di, mac and reg.  It is intended that this
	      covers all warnings that are useful with traditional macro pack‐
	      ages.

       w      All warnings.

   Incompatibilities
       Long names cause some incompatibilities.	 Unix troff will interpret

	      .dsabcd

       as  defining  a	string	ab with contents cd.  Normally, GNU troff will
       interpret this as a call of a macro named dsabcd.  Also Unix troff will
       interpret  \*[  or  \n[	as  references	to a string or number register
       called [.  In GNU troff, however, this will normally be interpreted  as
       the  start of a long name.  In compatibility mode GNU troff will inter‐
       pret these things in the traditional way.  In compatibility mode,  how‐
       ever,  long names are not recognised.  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.

       GNU  troff  does	 not  allow  the   use	 of   the   escape   sequences
       \\|\^\&\}\{\(space)\'\`\-\_\!\%\c  in  names of strings, macros, diver‐
       sions, number registers, fonts or environments; Unix troff  does.   The
       \A  escape  sequence  may  be  helpful  in avoiding use of these escape
       sequences in names.

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

	      .ps 10u

       will  set  the pointsize to 10 points, whereas in GNU troff it will set
       the pointsize to 10 scaled points.

       In GNU troff there is a	fundamental  difference	 between  unformatted,
       input  characters,  and	formatted, output characters.  Everything that
       affects how an output character will be output is stored with the char‐
       acter;  once  an output character has been constructed it is unaffected
       by any subsequent requests that are executed, including	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 output characters in any combination.  An output charac‐
       ter 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.   For
       example,

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

       will  print  \\	in GNU troff; each pair of input \s is turned into one
       output \ and the resulting output \s  are  not  interpreted  as	escape
       characters  when	 they  are reread.  Unix troff would interpret them as
       escape characters when they were reread and would end up	 printing  one
       \.   The	 correct  way  to obtain a printable \ is to use the \e escape
       sequence: this will always print	 a  single  instance  of  the  current
       escape  character,  regardless of whether or not it is used in a diver‐
       sion; it will also work in both GNU troff and Unix troff.  If you  wish
       for some reason to store in a diversion an escape sequence that will be
       interpreted when the diversion is reread, you can either use the tradi‐
       tional  \!  transparent output facility, or, if this is unsuitable, the
       new \?  escape sequence.

ENVIRONMENT
       GROFF_TMAC_PATH
	      A colon separated list of directories in	which  to  search  for
	      macro files.

       GROFF_TYPESETTER
	      Default device.

       GROFF_FONT_PATH
	      A colon separated list of directories in which to search for the
	      devname directory.  troff will search in	directories  given  in
	      the  -F option before these, and in standard directories (@FONT‐
	      PATH@) after these.

FILES
       @MACRODIR@/troffrc	Initialization file

       @MACRODIR@/tmac.name	Macro files

       @FONTDIR@/devname/DESC	Device description file for device name.

       @FONTDIR@/devname/F	Font file for font F of device name.

SEE ALSO
       groff(@MAN1EXT@)		@g@tbl(@MAN1EXT@),	    @g@pic(@MAN1EXT@),
       @g@eqn(@MAN1EXT@),	  grops(@MAN1EXT@),	    grodvi(@MAN1EXT@),
       grotty(@MAN1EXT@),     groff_font(@MAN5EXT@),	 groff_out(@MAN5EXT@),
       groff_char(@MAN7EXT@)

Groff Version @VERSION@		    @MDATE@			   @G@TROFF(1)
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