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man pages section 7: Standards, Environments, Macros, Character Sets, and Miscellany

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groff_diff (7)

Name

groff_diff - differences between GNU troff and classical troff

Synopsis

Please see following description for synopsis

Description

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 processing system, and the classical  roff  formatter  of
       the  freely  available  Unix  7  of  the 1970s, documented in the Troff
       User's Manual by Ossanna and Kernighan.  This includes  the  roff  lan-
       guage as well as the intermediate output format (troff output).

       The  section SEE ALSO gives pointers to both the classical roff and the
       modern groff documentation.

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

   Long names
       The  names  of number registers, fonts, strings/macros/diversions, spe-
       cial characters (glyphs), and colors can be of any length.   In  escape
       sequences,  additionally to the classical `(xx' construction for a two-
       character glyph name, you can use  `[xxx]'  for  a  name  of  arbitrary
       length.

       \[xxx] Print the special character (glyph) called xxx.

       \[comp1 comp2 ...]
              Print  composite glyph consisting of multiple components.  Exam-
              ple: `\[A ho]' is capital letter A  with  ogonek  which  finally
              maps  to  glyph  name `u0041_0328'.  See the groff info file for
              details how a glyph name for a composite glyph  is  constructed,
              and  groff_char(7)  for  a list of glyph name components used in
              composite glyph names.

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

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

       \n[xxx]
              Interpolate number register xxx.

   Fractional point sizes
       A scaled point is equal to 1/sizescale points, where sizescale is spec-
       ified in the DESC file (1 by default).  There is a  new  scale  indica-
       tor  z  that  has the effect of multiplying by sizescale.  Requests and
       escape sequences in troff interpret arguments that  represent  a  point
       size  as  being  in units of scaled points, but they evaluate each such
       argument using a default scale indicator of z.   Arguments  treated  in
       this  way are the argument to the ps request, the third argument to the
       cs request, the second and fourth arguments to  the  tkf  request,  the
       argument to the \H escape sequence, and those variants of the \s escape
       sequence that take a numeric expression as their argument.

       For example, suppose sizescale is 1000; then a scaled point is  equiva-
       lent  to  a  millipoint; the call .ps 10.25 is equivalent to .ps 10.25z
       and so sets the point size to 10250 scaled points, which  is  equal  to
       10.25 points.

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

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

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

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

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

       e1>?e2 The maximum of e1 and e2.

       e1<?e2 The minimum of e1 and e2.

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

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

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

       \C'xxx'
              Typeset glyph named xxx.  Normally it is more convenient to  use
              \[xxx].   But  \C  has  the advantage that it is compatible with
              recent versions of UNIX and is available in compatibility mode.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              \O4    End a nesting level.

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

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

                     .nr name +-n

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

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

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

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

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

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

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

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

       \$^    In a macro, the representation of all parameters as if they were
              an argument to the ds request.

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

       \?anything\?
              When used in a diversion, this transparently embeds anything  in
              the  diversion.  anything is read in copy mode.  When the diver-
              sion is reread, anything is interpreted.  anything may not  con-
              tain  newlines; use \! if you want to embed newlines in a diver-
              sion.  The escape sequence \? is also recognized  in  copy  mode
              and  turned  into  a  single internal code; it is this code that
              terminates anything.  Thus

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

              prints 4.

       \/     This increases the width of the  preceding  glyph  so  that  the
              spacing between that glyph and the following glyph is correct if
              the following glyph is a roman glyph.  It is a good idea to  use
              this  escape  sequence  whenever  an italic glyph is immediately
              followed by a roman glyph without any intervening space.

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

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

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

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

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

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

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

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

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

       .ami1 xx yy
              Same as the ami request but compatibility mode is  switched  off
              during execution.

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

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

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

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

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

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

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

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

       .brp   This is the same as \p.

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

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

              2      Lines can be broken before the  character  (initially  no
                     characters have this property); a line is not broken at a
                     character with this property  unless  the  characters  on
                     each side both have non-zero hyphenation codes.  This can
                     be overridden with value 64.

              4      Lines can be broken after the character (initially  char-
                     acters  -\[hy]\[em]  have  this  property); a line is not
                     broken at a character with this property unless the char-
                     acters on each side both have non-zero hyphenation codes.
                     This can be overridden with value 64.

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

              16     The glyph associated with this character overlaps  verti-
                     cally (initially glyph \[br] has this property).

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

              64     Ignore hyphenation code values of the surrounding charac-
                     ters.  Use this in combination with values 2 and 4  (ini-
                     tially no characters have this property).

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

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

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

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

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

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

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

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

              A glyph definition can be removed with the rchar request.

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

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

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

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

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

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

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

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

                     .defcolor darkgreen rgb 0.1f 0.5f 0.2f

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

                     .defcolor darkgreen rgb 0.1 0.5 0.2

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

       .de1 xx yy
              Similar  to  .de,  but compatibility mode is switched off during
              execution.  On entry, the current compatibility  mode  is  saved
              and restored at exit.

       .dei xx yy
              Define macro indirectly.  The following example

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

              is equivalent to

                     .de aa bb

       .dei1 xx yy
              Similar  to  the  dei request but compatibility mode is switched
              off during execution.

       .device anything
              This is (almost) the same as the \X escape.  anything is read in
              copy mode; a leading " is stripped.

       .devicem xx
              This  is  the  same as the \Y escape (to embed the contents of a
              macro into the intermediate output preceded with `x X').

       .do xxx
              Interpret .xxx with compatibility mode disabled.  For example,

                     .do fam T

              would have the same effect as

                     .fam T

              except that it would work even if compatibility  mode  had  been
              enabled.   Note that the previous compatibility mode is restored
              before any files sourced by xxx are interpreted.

       .ds1 xx yy
              Similar to .ds, but compatibility mode is  switched  off  during
              expansion.   To be more precise, a `compatibility save' token is
              inserted at the beginning of the string,  and  a  `compatibility
              restore' token at the end.

       .ecs   Save current escape character.

       .ecr   Restore  escape  character  saved  with ecs.  Without a previous
              call to ecs, `\' will be the new escape character.

       .evc xx
              Copy the contents of environment xx to the current  environment.
              No pushing or popping of environments is done.

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

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

       .fcolor c
              Set the fill color to c.  If c is missing, switch to the  previ-
              ous fill color.

       .fschar f c string
              Define  fallback character (or glyph) c for font f to be string.
              The syntax of this request is the same as the char request (with
              an  additional  argument  to  specify the font); a glyph defined
              with fschar is searched after the list of  fonts  declared  with
              the  fspecial request but before the list of fonts declared with
              .special.

       .fspecial f s1 s2 ...
              When the current font is f, fonts s1, s2, ..., are special, that
              is,  they  are searched for glyphs not in the current font.  Any
              fonts specified in the special request are searched after  fonts
              specified  in the fspecial request.  Without argument, reset the
              list of global special fonts to be empty.

       .ftr f g
              Translate font f to g.  Whenever a font named f is  referred  to
              in  an \f escape sequence, in the F and S conditional operators,
              or in the ft, ul, bd, cs, tkf, special,  fspecial,  fp,  or  sty
              requests,  font  g is used.  If g is missing, or equal to f then
              font f is not translated.

       .fzoom f zoom
              Set zoom factor zoom for font f.  zoom must a non-negative inte-
              ger multiple of 1/1000th.  If it is missing or is equal to zero,
              it means the same as 1000, namely no magnification.  f must be a
              real font name, not a style.

       .gcolor c
              Set the glyph color to c.  If c is missing, switch to the previ-
              ous glyph color.

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

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

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

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

              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  com-
                     ment).

              Use  the hpfcode request to map the encoding used in hyphenation
              patterns files to groff's input encoding.   By  default,  every-
              thing  maps to itself except letters `A' to `Z' which map to `a'
              to `z'.

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

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

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

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

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

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

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

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

       .linetabs n
              If  n  is  non-zero or missing, enable line-tabs mode, otherwise
              disable it (which is the default).  In line-tabs mode, tab  dis-
              tances are computed relative to the (current) output line.  Oth-
              erwise they are taken relative to the input line.  For  example,
              the following

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

              yields

                     a         b         c

              In line-tabs mode, the same code gives

                     a         b                   c

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

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

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

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

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

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

       .opena stream filename
              Like open, but if filename exists, append to it instead of trun-
              cating it.

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

       .pev   Print the current environment and each defined environment state
              on stderr.

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

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

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

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

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

              The total vertical line spacing consists of four components: .vs
              and  \x  with a negative value which are applied before the line
              is output, and .pvs and \x  with  a  positive  value  which  are
              applied after the line is output.

       .rchar c1 c2 ...
              Remove  the  definitions  of  glyphs c1, c2, ... This undoes the
              effect of a char request.

       .return
              Within a macro, return immediately.  If called with an argument,
              return  twice,  namely from the current macro and from the macro
              one level higher.  No effect otherwise.

       .rfschar c1 c2 ...
              Remove the font-specific definitions of glyphs c1, c2, ...  This
              undoes the effect of a fschar request.

       .rj
       .rj n  Right justify the next n input lines.  Without an argument right
              justify the next input line.  The number of lines  to  be  right
              justified is available in the \n[.rj] register.  This implicitly
              does .ce 0.  The ce request implicitly does .rj 0.

       .rnn xx yy
              Rename number register xx to yy.

       .schar c string
              Define global fallback character (or glyph) c to be string.  The
              syntax  of this request is the same as the char request; a glyph
              defined with schar is searched after the list of fonts  declared
              with the special request but before the mounted special fonts.

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

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

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

       .special s1 s2 ...
              Fonts  s1,  s2, ..., are special and are searched for glyphs not
              in the current font.  Without arguments, reset the list of  spe-
              cial fonts to be empty.

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

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

       .substring xx n1 [n2]
              Replace  the  string  named xx with the substring defined by the
              indices n1 and n2.   The  first  character  in  the  string  has
              index  0.   If  n2  is  omitted,  it is taken to be equal to the
              string's length.  If the index value n1 or n2 is negative, it is
              counted  from  the  end of the string, going backwards: The last
              character has index -1, the character before the last  character
              has index -2, etc.

       .tkf f s1 n1 s2 n2
              Enable track kerning for font f.  When the current font is f the
              width of every glyph is increased by an amount  between  n1  and
              n2;  when the current point size is less than or equal to s1 the
              width is increased by n1; when it is greater than or equal to s2
              the  width  is  increased  by n2; when the point size is greater
              than or equal to s1 and less than or equal to s2 the increase in
              width is a linear function of the point size.

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

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

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

                     .di x
                     .trf f
                     .di

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

       .trin abcd
              This is the same as the  tr  request  except  that  the  asciify
              request  uses  the  character code (if any) before the character
              translation.  Example:

                     .trin ax
                     .di xxx
                     a
                     .br
                     .di
                     .xxx
                     .trin aa
                     .asciify xxx
                     .xxx

              The result is x a.  Using tr, the result would be x x.

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

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

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

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

       .unformat xx
              This  request  `unformats'  the  diversion  xx.  Contrary to the
              asciify request, which tries to convert  formatted  elements  of
              the  diversion back to input tokens as much as possible, .unfor-
              mat only handles tabs and spaces between words  (usually  caused
              by  spaces  or newlines in the input) specially.  The former are
              treated as if  they  were  input  tokens,  and  the  latter  are
              stretchable  again.  Note that the vertical size of lines is not
              preserved.  Glyph information (font,  font  size,  space  width,
              etc.)  is retained.  Useful in conjunction with the box and boxa
              requests.

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

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

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

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

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

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

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

   Extended escape sequences
       \D'...'
              All  drawing  commands  of  groff's  intermediate   output   are
              accepted.  See subsection Drawing Commands below for more infor-
              mation.

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

       .de xx yy
       .am xx yy
       .ds xx yy
       .as xx yy
              In  compatibility  mode, these requests behaves similar to .de1,
              .am1, .ds1, and .as1, respectively: A `compatibility save' token
              is  inserted  at  the  beginning,  and a `compatibility restore'
              token at the end, with compatibility  mode  switched  on  during
              execution.

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

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

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

                     .ta T .5i

              sets tabs every half an inch.

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

       \n[.br]
              Within  a macro call, it is set to 1 if the macro is called with
              the `normal' control character (`.' by default), and  set  to  0
              otherwise.  This allows to reliably modify requests.

                     .als bp*orig bp
                     .de bp
                     .tm before bp
                     .ie \\n[.br] .bp*orig
                     .el 'bp*orig
                     .tm after bp
                     ..

              Using this register outside of a macro makes no sense (it always
              returns zero in such cases).

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

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

       \n[.ce]
              The  number  of lines remaining to be centered, as set by the ce
              request.

       \n[.cht]
              The height of the last glyph added to the  current  environment.
              It is positive if the glyph extends above the baseline.

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

       \n[.csk]
              The  skew  of  the  last glyph added to the current environment.
              The skew of a glyph is how far to the right of the center  of  a
              glyph the center of an accent over that glyph should be placed.

       \n[.ev]
              The  name  or  number  of  the  current  environment.  This is a
              string-valued register.

       \n[.fam]
              The current font family.  This is a string-valued register.

       \n[.fn]
              The current (internal) real font name.  This is a  string-valued
              register.   If the current font is a style, the value of \n[.fn]
              is the proper concatenation of family and style name.

       \n[.fp]
              The number of the next free font position.

       \n[.g] Always 1.  Macros should use this to determine whether they  are
              running under GNU troff.

       \n[.height]
              The current height of the font as set with \H.

       \n[.hla]
              The current hyphenation language as set by the hla request.

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

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

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

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

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

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

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

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

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

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

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

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

       \n[.m] The name of the current drawing color.  This is a  string-valued
              register.

       \n[.M] The name of the current background color.  This is a string-val-
              ued register.

       \n[.ne]
              The amount of space that was needed in the last ne request  that
              caused  a  trap  to  be  sprung.  Useful in conjunction with the
              \n[.trunc] register.

       \n[.ns]
              1 if no-space mode is active, 0 otherwise.

       \n[.O] The current output level as set with \O.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       Other available read/write number registers are:

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

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

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

       \n[lsn]
       \n[lss]
              If  there  are  leading spaces in an input line, these registers
              hold the number of leading spaces and the corresponding horizon-
              tal space, respectively.

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

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

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

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

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

   Miscellaneous
       troff  predefines  a single (read/write) string-based register, \*[.T],
       which contains the argument given to the -T command line option, namely
       the  current  output  device (for example, latin1 or ascii).  Note that
       this is not the same as the (read-only) number register \n[.T] which is
       defined to be 1 if troff is called with the -T command line option, and
       zero otherwise.  This behaviour is different to UNIX troff.

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

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

              .xx \\$@

       is

              \\*[xx]\\

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

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

       There are some new types of condition:

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

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

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

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

       .if Ff True  if  font  f exists.  f is handled as if it was opened with
              the ft  request  (this  is,  font  translation  and  styles  are
              applied), without actually mounting it.

       .if Ss True  if  style  s  has  been  registered.   Font translation is
              applied.

       The tr request can now map characters onto \~.

       The space width emitted by the \| and \^ escape sequences can  be  con-
       trolled  on  a  per-font  basis.   If  there is a glyph named \| or \^,
       respectively (note the leading backslash), defined in the current  font
       file, use this glyph's width instead of the default value.

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

              .if t \{\
              .  de bar
              .    nop Hello, I'm `bar'.
              .  .
              .\}

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

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

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

       If  the  tcommand line is present in the DESC file, troff uses the fol-
       lowing two commands.

       txxx   xxx is any sequence of characters terminated by  a  space  or  a
              newline  (to  be  more precise, it is a sequence of glyphs which
              are accessed with the corresponding characters); the first char-
              acter  should  be  printed  at the current position, the current
              horizontal position should be increased  by  the  width  of  the
              first character, and so on for each character.  The width of the
              glyph is that given in the font file, appropriately  scaled  for
              the  current point size, and rounded so that it is a multiple of
              the horizontal resolution.  Special characters cannot be printed
              using this command.

       un xxx This  is  same  as the t command except that after printing each
              character, the current horizontal position is increased  by  the
              sum of the width of that character and n.

       Note  that  single  characters  can have the eighth bit set, as can the
       names of fonts and special characters.

       The names of glyphs and fonts  can  be  of  arbitrary  length;  drivers
       should not assume that they are only two characters long.

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

       For color support, some new commands have been added:

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

       The x device control command has been extended.

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

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

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

              The  corresponding  \D'f...' command shouldn't be used since its
              argument is always rounded to an integer multiple of  the  hori-
              zontal resolution which can lead to surprising results.

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

       DE dx dy\n
              Draw a solid ellipse with a horizontal diameter of dx and a ver-
              tical  diameter  of  dy  with  the leftmost point at the current
              position.  delim $$

       Dp $dx sub 1$ $dy sub 1$ $dx sub 2$ $dy sub 2$ $...$ $dx sub n$ $dy sub
       n$\n
              Draw  a  polygon with, for $i = 1 ,..., n+1$, the i-th vertex at
              the current position $+ sum from j=1 to i-1 ( dx sub j , dy  sub
              j )$.  At the moment, GNU pic only uses this command to generate
              triangles and rectangles.

       DP $dx sub 1$ $dy sub 1$ $dx sub 2$ $dy sub 2$ $...$ $dx sub n$ $dy sub
       n$\n
              Like Dp but draw a solid rather than outlined polygon.

       Dt n\n Set  the  current line thickness to n machine units.  Tradition-
              ally Unix troff drivers use a line thickness proportional to the
              current  point size; drivers should continue to do this if no Dt
              command has been given, or if a Dt command has been given with a
              negative  value  of  n.   A zero value of n selects the smallest
              available line thickness.

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

              \D'c  $x sub 1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x sub n$ $y
              sub n$'

       where c is not one of c, e, l, a, or ~, Unix troff treats each  of  the
       $x sub i$ as a horizontal quantity, and each of the $y sub i$ as a ver-
       tical quantity and assumes that the width of the drawn object  is  $sum
       from i=1 to n x sub i$, and that the height is $sum from i=1 to n y sub
       i$.  (The assumption about the height can be seen by examining  the  st
       and sb registers after using such a D command in a \w escape sequence).
       This rule also holds for all the original  drawing  commands  with  the
       exception  of De.  For the sake of compatibility GNU troff also follows
       this rule, even though it produces an ugly result in the case of the Dt
       and  Df,  and, to a lesser extent, DE commands.  Thus after executing a
       D command of the form

              Dc $x sub 1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x  sub  n$  $y
              sub n$\n

       the  current position should be increased by $( sum from i=1 to n x sub
       i , sum from i=1 to n y sub i )$.

       Another set of extensions is

       DFc cyan magenta yellow\n
       DFd\n
       DFg gray\n
       DFk cyan magenta yellow black\n
       DFr red green blue\n
              Set the color components of the filling  color  similar  to  the
              m commands above.

       The  current  position isn't changed by those colour commands (contrary
       to Df).

   Device Control Commands
       There is a continuation convention which permits the  argument  to  the
       x X  command  to  contain newlines: when outputting the argument to the
       x X command, GNU troff follows each newline in the argument  with  a  +
       character (as usual, it terminates the entire argument with a newline);
       thus if the line after the line containing the x X command starts  with
       +,  then  the newline ending the line containing the x X command should
       be treated as part of the argument to the x X command, the + should  be
       ignored,  and  the  part  of the line following the + should be treated
       like the part of the line following the x X command.

       The first three output commands are guaranteed to be:

              x T device
              x res n h v
              x init

INCOMPATIBILITIES
       In spite of the many extensions, groff has  retained  compatibility  to
       classical  troff to a large degree.  For the cases where the extensions
       lead to collisions, a special compatibility mode with  the  restricted,
       old functionality was created for groff.

   Groff Language
       groff  provides  a  compatibility mode that allows to process roff code
       written for classical troff or for other implementations of roff  in  a
       consistent way.

       Compatibility  mode  can  be turned on with the -C command line option,
       and turned on or off with the .cp request.  The number  register  \n(.C
       is 1 if compatibility mode is on, 0 otherwise.

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

              .dsabcd

       as defining a string ab with contents cd.  In groff mode, this is  con-
       sidered as a call of a macro named dsabcd.

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

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

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

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

       Fractional  point sizes cause one noteworthy incompatibility.  In clas-
       sical troff, the ps request ignores scale indicators and so

              .ps 10u

       sets the point size to 10 points, whereas  in  groff  native  mode  the
       point size is set to 10 scaled points.

       In  groff,  there is a fundamental difference between unformatted input
       characters, and formatted output characters (glyphs).  Everything  that
       affects  how  a  glyph is output is stored with the glyph; once a glyph
       has been constructed it is unaffected by any subsequent  requests  that
       are executed, including the bd, cs, tkf, tr, or fp requests.

       Normally  glyphs  are  constructed  from input characters at the moment
       immediately before the glyph is  added  to  the  current  output  line.
       Macros,  diversions  and  strings  are  all,  in fact, the same type of
       object; they contain lists of input characters and glyphs in any combi-
       nation.

       Special  characters can be both; before being added to the output, they
       act as input entities, afterwards they denote glyphs.

       A glyph does not behave like an input character  for  the  purposes  of
       macro  processing;  it  does  not inherit any of the special properties
       that the input character from which it was constructed might have  had.
       The following example makes things clearer.

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

       With  GNU  troff  this  is  printed as \\.  So each pair of input back-
       slashes `\\' is turned into a single output backslash glyph `\' and the
       resulting  output  backslashes are not interpreted as escape characters
       when they are reread.

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

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

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

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

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

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


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | text/groff       |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+
SEE ALSO
       The  groff  info  file,  cf.  info(1)  presents all groff documentation
       within a single document.

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

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

                     man 7 groff

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

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

COPYING
       Copyright (C) 1989-2014 Free Software Foundation, Inc.

       This file is part of groff, the GNU roff type-setting  system.   It  is
       the source of the man-page groff_diff(7).

       Permission  is  granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version  1.3  or
       any  later  version  published by the Free Software Foundation; with no
       Front-Cover Texts, and with no Back-Cover Texts.

       A copy of the Free Documentation License is included as a  file  called
       FDL  in  the  main  directory  of  the groff source package, it is also
       available in the  internet  at  GNU  FDL  license  <http://www.gnu.org/
       copyleft/fdl.html>.

AUTHORS
       This document was written by James Clark <jjc@jclark.com>, was modified
       by   Werner   Lemberg   <wl@gnu.org>   and   Bernd    Warken    <groff-
       bernd.warken-72@web.de>.



NOTES
       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source                was                downloaded                from
       https://ftp.gnu.org/gnu/groff/groff-1.22.3.tar.gz

       Further information about this software can be found on the open source
       community website at https://www.gnu.org/software/groff.



Groff Version 1.22.3            4 November 2014                  GROFF_DIFF(7)