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groff_diff(7)                                                    groff_diff(7)




NAME

       groff_diff - differences between GNU troff and classical troff


DESCRIPTION

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

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


GROFF LANGUAGE

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

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

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

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

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

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

       \n[xxx]
              Interpolate number register xxx.

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

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

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

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

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

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

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

       e1>?e2 The maximum of e1 and e2.

       e1<?e2 The minimum of e1 and e2.

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

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

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

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

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

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

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

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

       \mx    \m(xx \m[xxx] Set drawing color.  \m[] switches back to the pre-
              vious 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 vari-
              able 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  inter-
              preted;  also  it is permitted for xxx to have been defined as a
              macro and thus contain newlines (it is  not  permitted  for  the
              argument  to \X to contain newlines).  The inclusion of newlines
              requires an extension to the UNIX troff output format, and  con-
              fuses 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 diver-
              sion.

       .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, respec-
              tively: A `compatibility save' token is inserted at  the  begin-
              ning,  and a `compatibility restore' token at the end, with com-
              patibility 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 reg-
              isters hold the number of leading spaces and  the  corresponding
              horizontal space, respectively.

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

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

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

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

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

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

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

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

              .xx \\$@

       is

              \\*[xx]\\

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

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

       There are some new types of condition:

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

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

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

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

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

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

       The tr request can now map characters onto \~.

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

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

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


INTERMEDIATE OUTPUT FORMAT

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

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

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

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

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

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

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

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

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

       For color support, some new commands have been added:

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

       The x device control command has been extended.

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

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

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

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

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

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

       Dp dx1 dy1 dx2 dy2 ... dxn dyn\n
              Draw  a  polygon  <i>i_1h,  for i=1,...,n+1, the i-th vertex at the
              current position + > (dxj,dyj).  At the  moment,  GNU  pic  only
                                j=1
              uses this command to generate triangles and rectangles.

       DP dx1 dy1 dx2 dy2 ... dxn dyn\n
              Like Dp but draw a solid rather than outlined polygon.

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

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

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

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

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

       Another set of extensions is

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

       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.


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


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


AUTHORS

       This document was written by James Clark was modified by Werner Lemberg
       and Bernd Warken



Groff Version 1.22.3            4 November 2014                  groff_diff(7)

groff 1.22.3 - Generated Mon Oct 12 18:28:18 CDT 2015
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