TROFF(1)                                                              TROFF(1)



NAME
       troff - format documents

SYNOPSIS
       troff [ -abivzCERU ] [ -w ] [ -W ] [ -d ] [ -f ] [ -m ] [ -n ] [ -o ]
       [ -r ] [ -T ] [ -F ] [ -M ] [ files... ]

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

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

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

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

       -v     Print the version number.

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

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

       -E     Inhibit all error messages.

       -z     Suppress formatted output.

       -C     Enable compatibility mode.

       -dcs   

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

       -ffam  Use fam as the default font family.

       -mname Read in the file tmac.name. Normally this will be searched for
              in /usr/local/share/tmac.  By default is used the safer macro
              (reverted using -U ).

       -U     Unsafe option, avoids default use of safer macro.

       -R     Don't load troffrc.

       -nnum  Number the first page num.

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

       -rcn   

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

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

       -Fdir  Search dir for subdirectories devname (name is the name of the
              device) for the DESC file and font files before the normal
              /usr/local/share/groff_font.

       -Mdir  Search directory dir for macro files before the normal
              /usr/local/share/tmac.

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

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

       \[xxx] Print the special character called xxx.

       \f[xxx]
              Set font xxx.

       \*[xxx]
              Interpolate string xxx.

       \n[xxx]
              Interpolate number register xxx.

   Fractional pointsizes
       A scaled point is equal to 1/sizescale points, where sizescale is
       specified in the DESC file (1 by default.)  There is a new scale
       indicator z which has the effect of multiplying by sizescale.  Requests
       and escape sequences in troff interpret arguments that represent a
       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 request .ps 10.25 is equivalent to .ps
       10.25z and so sets the pointsize to 10250 scaled points, which is equal
       to 10.25 points.

       The number register \n(.s returns the pointsize in points as 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.

       e1>?e2 The maximum of e1 and e2.

       e1<?e2 The minimum of e1 and e2.

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

   New escape sequences
       \A'anything'
              This expands to 1 or 0 according as anything is or is not
              acceptable as the name of a string, macro, diversion, number
              register, environment or font.  It will return 0 if anything is
              empty.  This is useful if you want to lookup user input in some
              sort of associative table.

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

       \E     This is equivalent to an escape character, but it's not
              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.)

       \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 on conjunction
              with the char request:

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


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

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

                     .nr name +-n

       \s(nn  

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

       \s[+-n]
              

       \s+-[n]
              

       \s'+-n'
              

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

       \Vx    

       \V(xx  

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

       \Yx    

       \Y(xx  

       \Y[xxx]
              This is approximately equivalent to \X'\*[xxx]'. However the
              contents of the string or macro xxx are not interpreted; also it
              is permitted for xxx to have been defined as a macro and thus
              contain newlines (it is not permitted for the argument to \X to
              contain newlines).  The inclusion of newlines requires an
              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, the concatenation of all the arguments separated by
              spaces.

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

       \$(nn  

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

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


              will print 4.

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

       \,     This modifies the spacing of the following character so that the
              spacing between that character and the preceding character will
              correct if the preceding character is a roman character.  For
              example, inserting \, between the parenthesis and the f changes
              (f to (f.  It is a good idea to use this escape sequence
              whenever a roman character is immediately followed by an italic
              character without any intervening space.

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

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

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

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

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

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

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


              will set register n to 1.

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

       .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.

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

       .cflags n c1 c2...
              Characters c1, c2,... have properties determined by n, which is
              ORed from the following:
              1      the character ends sentences (initially characters .?!
                     have this property);

              2      lines can be broken before the character (initially no
                     characters have this property); 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 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
                     s')]*\(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.

       .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.

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

                     .do fam T

              would have the same effect as


                     .fam T

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

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

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

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

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

       .hla lang
              Set the current hyphenation language to lang. Hyphenation
              exceptions specified with the hw request and hyphenation
              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 tmac.name is searched for when the -mname
              option is specified.  It should have the same format as the
              argument to the \patterns primitive in TeX; the letters
              appearing in this file are interpreted as hyphenation codes.  A
              % character in the patterns file introduces a comment that
              continues to the end of the line.  The set of hyphenation
              patterns is associated with the current language set by the hla
              request.  The hpf request is usually invoked by the troffrc
              file.

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

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

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

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

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

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

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

       .pso command
              This is 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.

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

       .rj    

       .rj n  Right justify the next n input lines.  Without an argument right
              justify the next input line.  The number of lines to be right
              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 hyphenated at a line break.  If the soft hyphen
              character does not exist in the font of the character
              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.

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

       .sty n f
              Associate style f with font position n. A font position can be
              associated either with a font or with a style.  The current font
              is the index of a font position and so is also either a font or
              a style.  When it is a style, the font that is actually used is
              the font the name of which is the concatenation of the name of
              the current family and the name of the current style.  For
              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.

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

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

                     .di x
                     .trf f
                     .di

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

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

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

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

       .vpt n Enable vertical position traps if n is non-zero, disable them
              otherwise.  Vertical position traps are traps set by the wh or
              dt requests.  Traps set by the it request are not vertical
              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
              the `Warnings' section.  For example, .warn 0 will disable all
              warnings, and .warn 1 will disable all warnings except that
              about missing characters.  If n is not given, all warnings will
              be enabled.

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

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

   Extended requests
       .cf filename
              When used in a diversion, this will embed in the diversion an
              object which, when reread, will cause the contents of filename
              to be transparently copied through to the output.  In Unix
              troff, the contents of filename is immediately copied through to
              the output regardless of whether there is a current diversion;
              this 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.

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

       .ss m n
              When two arguments are given to the ss request, the second
              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.  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[.csk]
              The skew of the last character added to the current environment.
              The skew of a character is how far to the right of the center of
              a character the center of an accent over that character should
              be placed.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       \n[.ss]
              

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

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

       \n[.warn]
              The sum of the numbers associated with each of the currently
              enabled warnings.  The number associated with each warning is
              listed in the `Warnings' subsection.

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

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

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

       \n[rst]
              

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

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

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

       The following read/write number registers are available:

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

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

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

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


              .xx \\$@

       is


              \\*[xx]\\

       If the font description file contains pairwise kerning information,
       characters from that font will be kerned.  Kerning between two
       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.  When decoding a macro
       argument that is delimited by double quotes, a character that appears
       at a different input level to the starting delimiter character will not
       be recognised as the closing delimiter character.  The implementation
       of \$@ ensures that the double quotes surrounding an argument will
       appear 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 cch
              True if there is a character ch available; ch is either an ASCII
              character or a special character \(xx or \[xxx]; the condition
              will also be true if ch has been defined by the char request.

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

       chart1 Non-existent characters.  This is enabled by default.

       numbert2
              Invalid numeric expressions.  This is enabled by default.

       breakt4
              In fill mode, lines which could not be broken so that their
              length was less than the line length.  This is enabled by
              default.

       delimt8
              Missing or mismatched closing delimiters.

       elt16  Use of the el request with no matching ie request.

       scalet32
              Meaningless scaling indicators.

       ranget64
              Out of range arguments.

       syntaxt128
              Dubious syntax in numeric expressions.

       dit256 Use of di or da without an argument when there is no current
              diversion.

       mact512
              Use of undefined strings, macros and diversions.  When an
              undefined string, macro or diversion is used, that string is
              automatically defined as empty.  So, in most cases, at most one
              warning will be given for each name.

       regt1024
              Use of undefined number registers.  When an undefined number
              register is used, that register is automatically defined to have
              a value of 0.  a definition is automatically made with a value
              of 0.  So, in most cases, at most one warning will be given for
              use of a particular name.

       tabt2048
              Inappropriate use of a tab character.  Either use of a tab
              character where a number was expected, or use of tab character
              in an unquoted macro argument.

       right-bracet4096
              Use of \} where a number was expected.

       missingt8192
              Requests that are missing non-optional arguments.

       inputt16384
              Illegal input characters.

       escapet32768
              Unrecognized escape sequences.  When an unrecognized escape
              sequence is encountered, the escape character is ignored.

       spacet65536
              Missing space between a request or macro and its argument.  This
              warning will be given when an undefined name longer than two
              characters is encountered, and the first two characters of the
              name make a defined name.  The request or macro will not be
              invoked.  When this warning is given, no macro is automatically
              defined.  This is enabled by default.  This warning will never
              occur in compatibility mode.

       fontt131072
              Non-existent fonts.  This is enabled by default.

       igt262144
              Illegal escapes in text ignored with the ig request.  These are
              conditions that are errors when they do not occur in ignored
              text.

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

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

       w      All warnings.

   Incompatibilities
       Long names cause some incompatibilities.  Unix troff will interpret


              .dsabcd

       as defining a string ab with contents cd. Normally, GNU troff will
       interpret this as a call of a macro named dsabcd. Also Unix troff will
       interpret \*[ or \n[ as references to a string or number register
       called [. In GNU troff, however, this will normally be interpreted as
       the start of a long name.  In compatibility mode GNU troff will
       interpret these things in the traditional way.  In compatibility mode,
       however, long names are not recognised.  Compatibility mode can be
       turned on with the -C command line option, and turned on or off with
       the cp request.  The number register \n(.C is 1 if compatibility mode
       is on, 0 otherwise.

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

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


              .ps 10u

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

       In GNU troff there is a fundamental difference between unformatted,
       input characters, and formatted, output characters.  Everything that
       affects how an output character will be output is stored with the
       character; once an output character has been constructed it is
       unaffected by any subsequent requests that are executed, including bd,
       cs, tkf, tr, or fp requests.  Normally output characters are
       constructed from input characters at the moment immediately before the
       character is added to the current output line.  Macros, diversions and
       strings are all, in fact, the same type of object; they contain lists
       of input characters and output characters in any combination.  An
       output 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.  For example,


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

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

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

       GROFF_TYPESETTER
              Default device.

       GROFF_FONT_PATH
              A colon separated list of directories in which to search for the
              devname directory.  troff will search in directories given in
              the -F option before these, and in standard directories
              (.:/usr/local/share/groff_font:/usr/lib/font) after these.

FILES
       /usr/local/share/tmac/troffrc
              Initialization file

       /usr/local/share/tmac/tmac.name
              Macro files

       /usr/local/share/groff_font/devname/DESC
              Device description file for device name.

       /usr/local/share/groff_font/devname/F
              Font file for font F of device name.

SEE ALSO
       groff(1) tbl(1), pic(1), eqn(1), grops(1), grodvi(1), grotty(1),
       grohtml(1), deroff(1), groff_font(5), groff_out(5), groff_char(7)



Groff Version 1.15                                                9 April 2000
