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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
       Osanna and Kernighan.  This inludes the roff language as well as the intermediate output format (troff output).

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

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

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

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

       \[xxx]    Print the special character called xxx.

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

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

       \n[xxx]   Interpolate number register xxx.

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

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

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

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

       There is also new scale indicator s which multiplies by the number of units in a scaled point.  So,  for  exam-
       ple, \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 def-
       initions 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 resp., depending on whether anything is or is not acceptable as the name of a
              string, macro, diversion, number register, environment, font, or color.  It will return 0 if anything is
              empty.  This is useful if you want to lookup user input in some sort of associative table.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              \O4    End a nesting level.

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

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

                     .nr name ?n

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

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

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

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

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

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

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

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

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

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

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

              will print 4.

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

       \,     This modifies the spacing of the following character so that the spacing between that character and  the
              preceding  character will correct if the preceding character is a roman character.  It is a good idea to
              use this escape sequence whenever a roman character is immediately followed by an italic character with-
              out 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 character.

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

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

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

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

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

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

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

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

       .as1 xx yy
              Similar to .as, but compatibility mode is switched off during expansion.  To be more precise, a 'compat-
              ibility 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 compat-
              ibility save/restore tokens only affect the (sub)strings defined by as1 and ds1.

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

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

       .box xx
       .boxa xx
              These  requests  are  similar  to the di and da requests with the exception that a partially filled line
              will not become part of the diversion (i.e., the diversion always starts with a new line)  but  restored
              after  ending  the  diversion, discarding the partially filled line which possibly comes from the 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
                     will not be broken at a character with this property unless the characters on each side both have
                     non-zero hyphenation codes.

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

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

              16     The character overlaps vertically (initially character \(br has this property).

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

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

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

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

              A character definition can be removed with the rchar request.

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

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

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

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

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

       .defcolor xxx scheme color_components
              Define color.  scheme can be one of the following values: rgb  (three  components),  cym  (three  compo-
              nents),  cmyk (four components), and gray or grey (one component).  Color components can be given either
              as a hexadecimal string or as positive decimal integers in the range 0-65535.  A hexadecimal string 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 specify color components as fractions in  the
              range 0 to 1.  Example:

                     .defcolor darkgreen rgb 0.1f 0.5f 0.2f

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

                     .defcolor darkgreen rgb 0.1 0.5 0.2

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

       .dei xx yy
              Define macro indirectly.  The following example

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

              is equivalent to

                     .de aa bb

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

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

                     .do fam T

              would have the same effect as

                     .fam T

              except that it would work even if compatibility mode had been enabled.  Note that the previous  compati-
              bility 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 'compat-
              ibility 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
              will be done.

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

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

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

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

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

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

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

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

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

              ?      No support for 'digraphs' like \$.

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

              ?      No macro expansion.

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

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

              ?      \endinput is recognized also.

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

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

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

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

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

       .hym n Set the hyphenation margin to n: when the current adjustment mode is not b, the line will not be hyphen-
              ated 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 hyphenation 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 register xx (which is not necessarily defined
              before).

       .linetabs n
              If n is non-zero or missing, enable line-tabs mode, otherwise disable it (which  is  the  default).   In
              line-tabs  mode,  tab  distances are computed relative to the (current) output line.  Otherwise 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.

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

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

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

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

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

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

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

       .psbb filename
              Get  the bounding box of a PostScript image filename.  This file must conform to Adobe's Document Struc-
              turing Conventions; the command looks for a %%BoundingBox comment to extract the  bounding  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 will be added to each
              line after it has been output.  With no argument, the post-vertical line space is set  to  its  previous
              value.

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

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

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

       .rnn xx yy
              Rename number register xx to yy.

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

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

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

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

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

       .sty n f
              Associate style f with font position n.  A font position can be associated either with a font or with  a
              style.   The current font is the index of a font position and so is also either a font or a style.  When
              it is a style, the font that is actually used is the font the name of which is the concatenation of  the
              name of the current family and the name of the current style.  For example, if the current font is 1 and
              font position 1 is associated with style R and the current font family is T, then font TR will be  used.
              If  the current font is not a style, then the current family is ignored.  When the requests cs, bd, tkf,
              uf, or fspecial are applied to a style, then they will instead be applied to the member of  the  current
              family  corresponding to that style.  The default family can be set with the -f option.  The styles com-
              mand 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 will be counted from the end of the string, going backwards: The last
              character has index -1, the character before the last character has index -2, etc.

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

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

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

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

                     .di x
                     .trf f
                     .di

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

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

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

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

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

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

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

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

       .unformat xx
              This  request  'unformats'  the  diversion xx.  Contrary to the .asciify request, which tries to convert
              formatted elements of the diversion back to input tokens as much as possible, .unformat will only handle
              tabs and spaces between words (usually caused by spaces or newlines in the input) specially.  The former
              are treated as if they were input tokens, and the latter are stretchable again.  Note that the  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 position traps.  The
              parameter that controls whether vertical position traps are enabled is global.  Initially vertical posi-
              tion traps are enabled.

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

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

       .while c anything
              While condition c is true, accept anything as input; c can be any condition 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 previously have been the subject of an open
              request.  anything is read in copy mode; a leading " will be stripped.

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

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

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

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

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

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

                     .ta T .5i

              will set tabs every half an inch.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       \n[.trunc]
              The amount of vertical space truncated by the most recently sprung vertical 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 actually is.  Useful in con-
              junction with the \n[.ne] register.

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

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

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

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

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

       \n[llx]
       \n[lly]
       \n[urx]
       \n[ury]
              These  four  registers  are  set by the .psbb request and contain the bounding box 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 characters.

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

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

       Other available read/write number registers are:

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

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

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

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

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

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

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

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

   Miscellaneous
       troff  predefines  a single (read/write) string-based register, \*(.T, which contains the argument given to the
       -T command line option, namely the current output device (for 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 com-
       mand 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 will not allow a font to be mounted at a position whose number is much greater than
       that of any currently used position.

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

              .xx \\$@

       is

              \\*[xx]\\

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

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

       There are some new types of condition:

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

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

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

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

       The tr request can now map characters onto \~.

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

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

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

   Units
       The  argument to the s command is in scaled points (units of points/n, where n is the 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 character with index n (a non-negative integer) of the current font.

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

       txxx   xxx is any sequence of characters terminated by a space or a newline;  the  first  character  should  be
              printed at the current position, the current horizontal position should be increased by the width of the
              first character, and so on for each character.  The width of the character is that  given  in  the  font
              file, appropriately scaled for the current point size, and rounded so that it is a multiple of the hori-
              zontal 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 characters and fonts can be of arbitrary length; drivers should not assume that they will be only
       two characters long.

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

       For color support, some new commands have been added:

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

       The x device control command has been extended.

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

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

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

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

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

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

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

       Dt n\n Set the current line thickness to n machine units.  Traditionally Unix troff drivers use a  line  thick-
              ness  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  com-
       mand of the form

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

       where c is not one of c, e, l, a, or ~, Unix troff will treat each of the xi as a horizontal quantity, and each
       of the yi as a vertical quantity and will assume that the width of the drawn object  is  i=1xi,  and  that  the
       height is i=1yi.  (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, 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 (i=1xi,i=1yi).

       Another set of extensions is

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

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

   Device Control Commands
       There is a continuation convention which permits the argument to the x X command to contain newlines: when out-
       putting the argument to the x X command, GNU troff will follow each newline in the argument with a +  character
       (as  usual,  it  will terminate the entire 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 or for other  imple-
       mentations 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 will be considered as a call of a macro named
       dsabcd.

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

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

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

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

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

              .ps 10u

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

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

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

       An output character 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 will make things clearer.

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

       In GNU mode this will be printed as \\.  So each pair of input backslashes '\\' is turned into a single  output
       backslash  '\'  and  the  resulting  output  backslashes are not 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 cur-
       rent escape character is not redefined.  It works in both GNU mode and compatibility mode, while  dirty  tricks
       like  specifying  a sequence of multiple backslashes do not work reliably; for the different handling in diver-
       sions, macro definitions, or text mode quickly leads to a confusion about the necessary number of  backslashes.

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

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

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

       ? The intermediate output cannot be rescaled to other devices as classical "device-independent" troff did.

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

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

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

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

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

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

              shell# man 7 groff

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

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



Groff Version 1.18.1.4           05 July 2002                    GROFF_DIFF(7)