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GROFF_DIFF(7)          Miscellaneous Information Manual          GROFF_DIFF(7)



NAME
       groff_diff - differences between GNU troff and classical troff

DESCRIPTION
       This manual page describes the language differences between groff, the
       GNU roff text 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.

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 (glyphs), 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.

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

       \[comp1 comp2 ...]
              Print composite glyph consisting of multiple components.
              Example: `\[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 list of glyph name components used
              composite glyph names.

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

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

       \n[xxx]
              Interpolate number register xxx.

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

       For example, suppose sizescale is 1000; then a scaled point will be
       equivalent to a 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 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<&lt;?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 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
              interpreted in copy-mode.  For example, strings to start and end
              superscripting could be defined like this

                     $*
                     $*

              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 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 will not be searched.  The \N escape
              sequence can be conveniently used in conjunction with the char
              request, for example

                     $*

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

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

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

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

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

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

              \O4    End a nesting level.

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

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

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

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

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

       \$(nn

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

       \?anything\?
              When used in a diversion, this will transparently embed anything
              in the diversion.  anything is read in copy mode.  When the
              diversion is reread, anything will be interpreted.  anything may
              not contain newlines; use \! if you want to embed 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

                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*

              will print 4.

       \/     This increases the width of the preceding glyph so that the
              spacing between that glyph and the following glyph will be
              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 will 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
              followed by an italic glyph without any intervening space.

       \)     Like \&&amp; 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 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
              `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.

       .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
              compatibility 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 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

                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*

              will set 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 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 diversion.

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

       .brp   This is the same as \p.

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

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

              2      Lines can be broken before the character (initially no
                     characters have this property); a line 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]\[radicalex]\[sqrtex] have this property).

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

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

       .char c string
              Define glyph c to be string. Every time glyph 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 glyphs in string.

              A glyph 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 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 glyph within
              the glyph's definition will be 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.

       .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,
              otherwise disable it.  In compatibility mode, long names are not
              recognised, and the incompatibilities caused by long names do
              not arise.

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

                     $*

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

                     $*

              The color named default (which is device-specific) can't be
              redefined.  It is possible that the default color for $* and $*
              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

                     $*
                     $*
                     $*

              is equivalent to

                     $*

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

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

                     $*

              would have the same effect as

                     $*

              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 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 glyph c to be string. The syntax of this request
              is the same as the char request; the only difference 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 previous
              fill color.

       .fschar f c string
              Define fallback 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,... will be special,
              that is, they will searched for glyphs not in the current font.
              Any fonts specified in the special request will be 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 will be used.  If g is missing, or equal to f
              then font f will not be translated.

       .gcolor c
              Set the glyph color to c. If c is missing, switch to the
              previous glyph color.

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

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

       .hlm n Set the maximum number of consecutive hyphenated lines to n. If
              n is negative, there is no maximum.  The default value is -1.
              This value is associated with the current environment.  Only
              lines output from an environment count towards the 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 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
                     comment).

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

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

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

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

       .hym n Set the hyphenation margin to n: when the current adjustment
              mode is not b, the line will not be hyphenated if the line is no
              more than n short.  The default hyphenation margin is 0.  The
              default scaling indicator for this request is m. The hyphenation
              margin is associated with the current environment.  The current
              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

                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*

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

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

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

       .special s1 s2...
              Fonts s1, s2, are special and will be searched for glyphs not in
              the current font.  Without arguments, reset the list of special
              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 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 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
              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 glyph 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

                     $*
                     $*
                     $*

              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:

                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*
                     $*

              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,

                     $*
                     $*
                     $*
                     $*
                     $*

              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
              position traps are enabled.

       .warn n
              Control warnings.  n is the sum of the numbers associated with
              each warning that is to be enabled; all other warnings will be
              disabled.  The number associated with each warning is listed in
              troff(1). For example, .warn 0 will disable all warnings, and
              .warn 1 will disable all warnings except that about missing
              glyphs.  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 escape sequences
       \D'...'
              All drawing commands of groff's intermediate output are
              accepted.  See subsection Drawing Commands below for more
              information.

   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.

       .de xx yy

       .am xx yy

       .ds xx yy

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

       .ev xx If xx is not a number, this 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,

                     $*

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

       \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[.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
              actually 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] 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 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
              argument, 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[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 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 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,
       glyphs from that font will be kerned.  Kerning between two glyphs can
       be inhibited by placing a \&&amp; 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 glyph ch available; ch is either an ASCII
              character or a glyph (special character) \(xx or \[xxx]; the
              condition will also be 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 \~.

       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:

              $*
              $*
              $*
              $*
              $*

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 glyph 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 (to be more precise, it is a sequence of glyphs which
              are accessed with the corresponding characters); 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
              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 will be only two characters long.

       When a glyph is to be printed, that glyph will always be 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:

       $*

       $*

       $*

       $*

       $*     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.

       $*     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.

       $*     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.

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

       $*     Draw a solid circle with a diameter of d with the leftmost point
              at the current position.

       $*     Draw a solid ellipse with a horizontal diameter of dx and a
              vertical diameter of dy with the leftmost point at the current
              position.  (delim$$)

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

       $*     Like Dp but draw a solid rather than outlined polygon.

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

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

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

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

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

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

       Another set of extensions is

       $*

       $*

       $*

       $*

       $*     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 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 troff or for other implementations of roff in a
       consistent way.

       Compatibility mode can be turned on with the command line option, and
       turned on or off with the $* request.  The number register $* 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

              $*

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

       Also classical troff interprets $* or $* 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 $* (character c) in names of strings, macros,
       diversions, number registers, fonts or environments, whereas classical
       troff does.

       The $* escape sequence can be helpful in avoiding these escape
       sequences in names.

       Fractional pointsizes cause one noteworthy incompatibility.  In
       classical troff, the $* 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, there is a fundamental difference between unformatted input
       characters, and formatted output characters (glyphs).  Everything that
       affects how a glyph will be output is stored with the glyph; once a
       glyph has been constructed it is unaffected by any subsequent requests
       that are executed, including the $* $* $* $* or $* 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
       combination.

       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 will make things clearer.

              $*
              $*
              $*
              $*
              $*

       With GNU troff this will be printed as $* So each pair of input
       backslashes $* 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 $* 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 $* escape sequence; this works if the current escape
       character is not redefined.  It works in both GNU mode and
       compatibility mode, while dirty tricks like specifying a sequence of
       multiple backslashes do not work reliably; for the different 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 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, 2003, 2004 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
       This document was written by James Clark, with modifications by and

       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#$*/

       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



Groff Version 1.19.2           February 6, 2006                  GROFF_DIFF(7)