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groff(7)

Miscellaneous Information Manual                                      GROFF(7)



NAME
       groff - a short reference for the GNU roff language

DESCRIPTION
       The  name  groff  stands for GNU roff and is the free implementation of
       the roff type-setting system.  See roff(7) for a survey and  the  back‐
       ground of the groff system.

       This document gives only short descriptions of the predefined roff lan‐
       guage elements as used in groff.  Both the classical features  and  the
       groff extensions are provided.

       Historically,  the roff language was called troff.  groff is compatible
       with the classical system and provides proper extensions.  So  in  GNU,
       the  terms  roff,  troff, and groff language could be used as synonyms.
       However troff slightly tends to refer more to  the  classical  aspects,
       whereas  groff  emphasizes  the GNU extensions, and roff is the general
       term for the language.

       This file is only a short version of the complete documentation that is
       found  in the groff info(1) file, which contains more detailed, actual,
       and concise information.

       The general syntax for writing groff documents is relatively easy,  but
       writing extensions to the roff language can be a bit harder.

       The roff language is line-oriented.  There are only two kinds of lines,
       control lines and text lines.  The control lines start with  a  control
       character,  by  default  a period “.”  or a single quote “'”; all other
       lines are text lines.

       Control lines represent commands, optionally with arguments.  They have
       the following syntax.  The leading control character can be followed by
       a command name; arguments, if any, are separated by spaces (but not tab
       characters) from the command name and among themselves, for example,

              .command_name arg1 arg2

       For  indentation, any number of space or tab characters can be inserted
       between the leading control character and the  command  name,  but  the
       control character must be on the first position of the line.

       Text  lines  represent the parts that is printed.  They can be modified
       by escape sequences, which are recognized by a leading  backslash  ‘\’.
       These  are  in-line  or  even in-word formatting elements or functions.
       Some of these take arguments separated by single quotes “'”, others are
       regulated by a length encoding introduced by an open parenthesis ‘(’ or
       enclosed in brackets ‘[’ and ‘]’.

       The roff language provides flexible instruments  for  writing  language
       extension,  such  as  macros.  When interpreting macro definitions, the
       roff system enters a special operating mode, called the copy mode.

       The copy mode behaviour can be quite tricky, but there are  some  rules
       that ensure a safe usage.

       1.     Printable  backslashes  must  be denoted as \e.  To be more pre‐
              cise, \e represents the current  escape  character.   To  get  a
              backslash glyph, use \(rs or \[rs].

       2.     Double all backslashes.

       3.     Begin all text lines with the special non-spacing character \&.

       This  does not produce the most efficient code, but it should work as a
       first measure.  For better strategies, see  the  groff  info  file  and
       groff_tmac(5).

       Reading roff source files is easier, just reduce all double backslashes
       to a single one in all macro definitions.

GROFF ELEMENTS
       The roff language elements add formatting information to a  text  file.
       The  fundamental  elements  are  predefined commands and variables that
       make roff a full-blown programming language.

       There  are  two  kinds  of  roff  commands,  possibly  with  arguments.
       Requests are written on a line of their own starting with a dot ‘.’  or
       a “'”, whereas Escape sequences are in-line functions and in-word  for‐
       matting elements starting with a backslash ‘\’.

       The  user  can define her own formatting commands using the de request.
       These commands are called  macros,  but  they  are  used  exactly  like
       requests.  Macro packages are pre-defined sets of macros written in the
       groff language.  A user's possibilities to create escape sequences her‐
       self is very limited, only special characters can be mapped.

       The  groff  language provides several kinds of variables with different
       interfaces.  There are pre-defined variables, but the user  can  define
       her own variables as well.

       String  variables  store character sequences.  They are set with the ds
       request and retrieved by the \* escape  sequences.   Strings  can  have
       variables.

       Register  variables  can  store  numerical values, numbers with a scale
       unit, and occasionally string-like objects.  They are set with  the  nr
       request and retrieved by the \n escape sequences.

       Environments  allow  the  user  to  temporarily store global formatting
       parameters like line length, font size, etc. for later reuse.  This  is
       done by the ev request.

       Fonts  are  identified  either by a name or by an internal number.  The
       current font is chosen by the ft request or by the \f escape sequences.
       Each  device  has  special fonts, but the following fonts are available
       for all devices.  R is the standard font Roman.  B is its bold counter‐
       part.   The italic font is called I and is available everywhere, but on
       text devices it is displayed as an  underlined  Roman  font.   For  the
       graphical  output devices, there exist constant-width pendants of these
       fonts, CR, CI, and CB.  On text devices, all  glyphs  have  a  constant
       width anyway.

       Glyphs  are  visual  representation forms of characters.  In groff, the
       distinction between those two elements is not  always  obvious  (and  a
       full discussion is beyond the scope of this man page).  A first approx‐
       imation is that glyphs have a specific size and colour  and  are  taken
       from  a specific font; they can't be modified any more – characters are
       the input, and glyphs are the output.  As soon as an  output  line  has
       been  generated,  it no longer contains characters but glyphs.  In this
       man page, we use either ‘glyph’ or ‘character’, whatever is more appro‐
       priate.

       Moreover,  there  are  some advanced roff elements.  A diversion stores
       (formatted) information into a macro for later  usage.   A  trap  is  a
       positional condition like a certain number of lines from page top or in
       a diversion or in the input.  Some action can be prescribed to  be  run
       automatically when the condition is met.

       More  detailed  information and examples can be found in the groff info
       file.

CONTROL CHARACTERS
       There is a small set of characters that have a special controlling task
       in certain conditions.

       .      A  dot  is  only special at the beginning of a line or after the
              condition in the requests if, ie, el, and while.   There  it  is
              the  control character that introduces a request (or macro).  By
              using the cc request, the control character can be set to a dif‐
              ferent character, making the dot ‘.’  a non-special character.

              In  all other positions, it just means a dot character.  In text
              paragraphs, it is advantageous to start each sentence at a  line
              of its own.

       '      The single quote has two controlling tasks.  At the beginning of
              a line and in the conditional requests it  is  the  non-breaking
              control character.  That means that it introduces a request like
              the dot, but with the  additional  property  that  this  request
              doesn't  cause  a  linebreak.  By using the c2 request, the non-
              break control character can be set to a different character.

              As a second task, it is the most commonly used argument  separa‐
              tor in some functional escape sequences (but any pair of charac‐
              ters not part of the argument do work).  In all other positions,
              it denotes the single quote or apostrophe character.  Groff pro‐
              vides a printable representation with the \(cq escape sequence.

       "      The double quote is used to enclose arguments in macros (but not
              in  requests and strings).  In the ds and as requests, a leading
              double quote in the argument is stripped off, making  everything
              else  afterwards  the  string  to  be  defined (enabling leading
              whitespace).  The escaped double quote \" introduces a  comment.
              Otherwise, it is not special.  Groff provides a printable repre‐
              sentation with the \(dq escape sequence.

       \      The backslash usually introduces an escape sequence (this can be
              changed  with  the ec request).  A printed version of the escape
              character is the \e escape; a backslash glyph can be obtained by
              \(rs.

       (      The  open  parenthesis  is only special in escape sequences when
              introducing an escape name or argument consisting of exactly two
              characters.   In groff, this behaviour can be replaced by the []
              construct.

       [      The opening bracket is only special in groff  escape  sequences;
              there  it is used to introduce a long escape name or long escape
              argument.  Otherwise, it is non-special, e.g. in macro calls.

       ]      The closing bracket is only special in groff  escape  sequences;
              there  it terminates a long escape name or long escape argument.
              Otherwise, it is non-special.

       space  Space characters are only functional characters.  They  separate
              the arguments in requests, macros, and strings, and the words in
              text lines.  They are subject to groff's horizontal spacing cal‐
              culations.   To get a defined space width, escape sequences like
              ‘\ ’ (this is the escape character followed by a space), \|, \^,
              or \h should be used.

       newline
              In  text  paragraphs,  newlines mostly behave like space charac‐
              ters.  Continuation lines can be specified by  an  escaped  new‐
              line,  i.e., by specifying a backslash ‘\’ as the last character
              of a line.

       tab    If a tab character occurs during text the  interpreter  makes  a
              horizontal  jump to the next pre-defined tab position.  There is
              a sophisticated interface for handling tab positions.

NUMERICAL EXPRESSIONS
       A numerical value is a signed or unsigned  integer  or  float  with  or
       without  an  appended scaling indicator.  A scaling indicator is a one-
       character abbreviation for a unit of measurement.  A number followed by
       a scaling indicator signifies a size value.  By default, numerical val‐
       ues do not have a scaling indicator, i.e., they are normal numbers.

       The roff language defines the following scaling indicators.

              c         Centimeter
              i         Inch
              P         Pica = 1/6 inch
              p         Point = 1/72 inch
              m         Em = the font size in points (approx. width of  letter
                        ‘m’)
              M         100th of an Em
              n         En = Em/2
              u         Basic unit for actual output device
              v         Vertical    line   space   in   basic   units   scaled
                        point = 1/sizescale of a point (defined in  font  DESC
                        file)
              f         Scale by 65536.

       Numerical  expressions are combinations of the numerical values defined
       above with the following  arithmetical  operators  already  defined  in
       classical troff.

              +         Addition
              -         Subtraction
              *         Multiplication
              /         Division
              %         Modulo
              =         Equals
              ==        Equals
              <         Less than
              >         Greater than
              <=        Less or equal
              >=        Greater or equal
              &         Logical and
              :         Logical or
              !         Logical not
              (         Grouping of expressions
              )         Close current grouping

       Moreover,  groff  added  the  following operators for numerical expres‐
       sions:

              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.

       For details see the groff info file.

CONDITIONS
       Conditions occur in tests raised by the if, ie, and the while requests.
       The following table characterizes the different types of conditions.

              N         A  numerical  expression N yields true if its value is
                        greater than 0.
              !N        True if the value of N is 0 (see below).
              's1's2'   True if string s1 is identical to string s2.
              !'s1's2'  True if string s1 is not identical to string  s2  (see
                        below).
              cch       True if there is a glyph ch available.
              dname     True  if  there  is  a  string,  macro,  diversion, or
                        request called name.
              e         Current page number is even.
              o         Current page number is odd.
              mname     True if there is a color called name.
              n         Formatter is nroff.
              rreg      True if there is a register named reg.
              t         Formatter is troff.
              Ffont     True if there exists a font named font.
              Sstyle    True if a style named style has been registered.

       Note that the !  operator may  only  appear  at  the  beginning  of  an
       expression, and negates the entire expression.  This maintains bug-com‐
       patibility with AT&T troff.

REQUESTS
       This section provides a short reference for  the  predefined  requests.
       In groff, request, macro, and string names can be arbitrarily long.  No
       bracketing or marking of long names is needed.

       Most requests take one or more arguments.  The arguments are  separated
       by  space  characters  (no tabs!); there is no inherent limit for their
       length or number.

       Some requests have optional arguments with a different behaviour.   Not
       all  of  these details are outlined here.  Refer to the groff info file
       and groff_diff(7) for all details.

       In the following request specifications, most argument names were  cho‐
       sen  to be descriptive.  Only the following denotations need clarifica‐
       tion.

              c         denotes a single character.
              font      a font either specified as a font name or a font  num‐
                        ber.
              anything  all  characters up to the end of the line or within \{
                        and \}.
              n         is a numerical expression that evaluates to an integer
                        value.
              N         is   an  arbitrary  numerical  expression,  signed  or
                        unsigned.
              ±N        has three meanings depending on  its  sign,  described
                        below.

       If  an  expression  defined  as ±N starts with a ‘+’ sign the resulting
       value of the expression is added to an already existing value  inherent
       to  the  related  request,  e.g.  adding  to a number register.  If the
       expression starts with a ‘-’ the value of the expression is  subtracted
       from the request value.

       Without  a  sign,  N replaces the existing value directly.  To assign a
       negative number either prepend 0 or  enclose  the  negative  number  in
       parentheses.

   Request Short Reference
       .         Empty line, ignored.  Useful for structuring documents.
       .\" anything
                 Complete line is a comment.
       .ab string
                 Print string on standard error, exit program.
       .ad       Begin  line  adjustment  for  output  lines in current adjust
                 mode.
       .ad c     Start line adjustment in mode c (c=l,r,c,b,n).
       .af register c
                 Assign format c to register (c=l,i,I,a,A).
       .aln alias register
                 Create alias name for register.
       .als alias object
                 Create alias name for request, string,  macro,  or  diversion
                 object.
       .am macro Append to macro until .. is encountered.
       .am macro end
                 Append to macro until .end is called.
       .am1 macro
                 Same  as  .am but with compatibility mode switched off during
                 macro expansion.
       .am1 macro end
                 Same as .am but with compatibility mode switched  off  during
                 macro expansion.
       .ami macro
                 Append  to a macro whose name is contained in the string reg‐
                 ister macro until .. is encountered.
       .ami macro end
                 Append to a macro indirectly.  macro and end are string  reg‐
                 isters whose contents are interpolated for the macro name and
                 the end macro, respectively.
       .ami1 macro
                 Same as .ami but with compatibility mode switched off  during
                 macro expansion.
       .ami1 macro end
                 Same  as .ami but with compatibility mode switched off during
                 macro expansion.
       .as stringvar anything
                 Append anything to stringvar.
       .as1 stringvar anything
                 Same as .as but with compatibility mode switched  off  during
                 string expansion.
       .asciify diversion
                 Unformat  ASCII characters, spaces, and some escape sequences
                 in diversion.
       .backtrace
                 Print a backtrace of the input on stderr.
       .bd font N
                 Embolden font by N-1 units.
       .bd S font N
                 Embolden Special Font S when current font is font.
       .blm      Unset the blank line macro.
       .blm macro
                 Set the blank line macro to macro.
       .box      End current diversion.
       .box macro
                 Divert to macro, omitting a partially filled line.
       .boxa     End current diversion.
       .boxa macro
                 Divert and append to macro, omitting a partially filled line.
       .bp       Eject current page and begin new page.
       .bp ±N    Eject current page; next page number ±N.
       .br       Line break.
       .brp      Break and spread output line.  Same as \p.
       .break    Break out of a while loop.
       .c2       Reset no-break control character to “'”.
       .c2 c     Set no-break control character to c.
       .cc       Reset control character to ‘.’.
       .cc c     Set control character to c.
       .ce       Center the next input line.
       .ce N     Center following N input lines.
       .cf filename
                 Copy contents of file filename unprocessed to  stdout  or  to
                 the diversion.
       .cflags mode c1 c2 ...
                 Treat characters c1, c2, ... according to mode number.
       .ch trap N
                 Change trap location to N.
       .char c anything
                 Define entity c as string anything.
       .chop object
                 Chop  the  last  character  off  macro,  string, or diversion
                 object.
       .class name c1 c2 ...
                 Assign a set of characters, character ranges, or classes  c1,
                 c2, ... to name.
       .close stream
                 Close the stream.
       .color    Enable colors.
       .color N  If N is zero disable colors, otherwise enable them.
       .composite from to
                 Map  glyph  name  from  to glyph name to while constructing a
                 composite glyph name.
       .continue Finish the current iteration of a while loop.
       .cp       Enable compatibility mode.
       .cp N     If N is zero disable compatibility mode, otherwise enable it.
       .cs font N M
                 Set constant character width mode for font to N/36  ems  with
                 em M.
       .cu N     Continuous underline in nroff, like .ul in troff.
       .da       End current diversion.
       .da macro Divert and append to macro.
       .de macro Define or redefine macro until .. is encountered.
       .de macro end
                 Define or redefine macro until .end is called.
       .de1 macro
                 Same  as  .de but with compatibility mode switched off during
                 macro expansion.
       .de1 macro end
                 Same as .de but with compatibility mode switched  off  during
                 macro expansion.
       .defcolor color scheme component
                 Define  or  redefine  a color with name color.  scheme can be
                 rgb, cym, cymk, gray, or grey.  component can be single  com‐
                 ponents  specified  as fractions in the range 0 to 1 (default
                 scaling indicator f), as a string  of  two-digit  hexadecimal
                 color  components  with  a leading #, or as a string of four-
                 digit hexadecimal components with two leading #.   The  color
                 default can't be redefined.
       .dei macro
                 Define  or  redefine  a  macro whose name is contained in the
                 string register macro until .. is encountered.
       .dei macro end
                 Define or redefine a macro indirectly.   macro  and  end  are
                 string  registers  whose  contents  are  interpolated for the
                 macro name and the end macro, respectively.
       .dei1 macro
                 Same as .dei but with compatibility mode switched off  during
                 macro expansion.
       .dei1 macro end
                 Same  as .dei but with compatibility mode switched off during
                 macro expansion.
       .device anything
                 Write anything to the intermediate output as a device control
                 function.
       .devicem name
                 Write  contents  of macro or string name uninterpreted to the
                 intermediate output as a device control function.
       .di       End current diversion.
       .di macro Divert to macro.
       .do name  Interpret .name with compatibility mode disabled.
       .ds stringvar anything
                 Set stringvar to anything.
       .ds1 stringvar anything
                 Same as .ds but with compatibility mode switched  off  during
                 string expansion.
       .dt N trap
                 Set  diversion  trap  to  position N (default scaling indica‐
                 tor v).
       .ec       Reset escape character to ‘\’.
       .ec c     Set escape character to c.
       .ecr      Restore escape character saved with .ecs.
       .ecs      Save current escape character.
       .el anything
                 Else part for if-else (ie) request.
       .em macro The macro is run after the end of input.
       .eo       Turn off escape character mechanism.
       .ev       Switch to previous environment and pop it off the stack.
       .ev env   Push down environment number or name env  to  the  stack  and
                 switch to it.
       .evc env  Copy  the contents of environment env to the current environ‐
                 ment.  No pushing or popping.
       .ex       Exit from roff processing.
       .fam      Return to previous font family.
       .fam name Set the current font family to name.
       .fc       Disable field mechanism.
       .fc a     Set field delimiter to a and pad glyph to space.
       .fc a b   Set field delimiter to a and pad glyph to b.
       .fchar c anything
                 Define fallback character (or glyph) c as string anything.
       .fcolor   Set fill color to previous fill color.
       .fcolor c Set fill color to c.
       .fi       Fill output lines.
       .fl       Flush output buffer.
       .fp n font
                 Mount font on position n.
       .fp n internal external
                 Mount font with long external name to short internal name  on
                 position n.
       .fschar f c anything
                 Define  fallback  character (or glyph) c for font f as string
                 anything.
       .fspecial font
                 Reset list of special fonts for font to be empty.
       .fspecial font s1 s2 ...
                 When the current font is font, then the fonts s1, s2, ... are
                 special.
       .ft       Return to previous font.  Same as \f[] or \fP.
       .ft font  Change  to  font name or number font; same as \f[font] escape
                 sequence.
       .ftr font1 font2
                 Translate font1 to font2.
       .fzoom font
                 Don't magnify font.
       .fzoom font zoom
                 Set zoom factor for font (in multiples of 1/1000th).
       .gcolor   Set glyph color to previous glyph color.
       .gcolor c Set glyph color to c.
       .hc       Remove additional hyphenation indicator character.
       .hc c     Set up additional hyphenation indicator character c.
       .hcode c1 code1 c2 code2 ...
                 Set the hyphenation code of character c1 to code1, that of c2
                 to code2, etc.
       .hla lang Set the current hyphenation language to lang.
       .hlm n    Set the maximum number of consecutive hyphenated lines to n.
       .hpf file Read hyphenation patterns from file.
       .hpfa file
                 Append hyphenation patterns from file.
       .hpfcode a b c d ...
                 Set input mapping for .hpf.
       .hw words List of words with exceptional hyphenation.
       .hy N     Switch to hyphenation mode N.
       .hym n    Set  the  hyphenation  margin  to  n (default scaling indica‐
                 tor m).
       .hys n    Set the hyphenation space to n.
       .ie cond anything
                 If cond then anything else goto .el.
       .if cond anything
                 If cond then anything; otherwise do nothing.
       .ig       Ignore text until .. is encountered.
       .ig end   Ignore text until .end is called.
       .in       Change to previous indentation value.
       .in ±N    Change indentation according to ±N (default  scaling  indica‐
                 tor m).
       .it N trap
                 Set an input-line count trap for the next N lines.
       .itc N trap
                 Same as .it but count lines interrupted with \c as one line.
       .kern     Enable pairwise kerning.
       .kern n   If n is zero, disable pairwise kerning, otherwise enable it.
       .lc       Remove leader repetition glyph.
       .lc c     Set leader repetition glyph to c.
       .length register anything
                 Write the length of the string anything to register.
       .linetabs Enable line-tabs mode (i.e., calculate tab positions relative
                 to output line).
       .linetabs n
                 If n is zero, disable line-tabs mode, otherwise enable it.
       .lf N     Set input line number to N.
       .lf N file
                 Set input line number to N and filename to file.
       .lg N     Ligature mode on if N>0.
       .ll       Change to previous line length.
       .ll ±N    Set line length according to ±N (default length 6.5i, default
                 scaling indicator m).
       .lsm      Unset the leading spaces macro.
       .lsm macro
                 Set the leading spaces macro to macro.
       .ls       Change to the previous value of additional intra-line skip.
       .ls N     Set  additional  intra-line  skip value to N, i.e., N-1 blank
                 lines are inserted after each text output line.
       .lt ±N    Length of title (default scaling indicator m).
       .mc       Margin glyph off.
       .mc c     Print glyph c after each text line at  actual  distance  from
                 right margin.
       .mc c N   Set  margin  glyph  to  c and distance to N from right margin
                 (default scaling indicator m).
       .mk register
                 Mark current vertical position in register.
       .mso file The same as .so except that file  is  searched  in  the  tmac
                 directories.
       .na       No output-line adjusting.
       .ne       Need a one-line vertical space.
       .ne N     Need N vertical space (default scaling indicator v).
       .nf       No filling or adjusting of output-lines.
       .nh       No hyphenation.
       .nm       Number mode off.
       .nm ±N [M [S [I]]]
                 In  line  number  mode,  set  number,  multiple, spacing, and
                 indentation.
       .nn       Do not number next line.
       .nn N     Do not number next N lines.
       .nop anything
                 Always process anything.
       .nr register ±N [M]
                 Define or modify register using ±N with auto-increment M.
       .nroff    Make the built-in conditions n true and t false.
       .ns       Turn on no-space mode.
       .nx       Immediately jump to end of current file.
       .nx filename
                 Immediately continue processing with file file.
       .open stream filename
                 Open filename for writing  and  associate  the  stream  named
                 stream with it.
       .opena stream filename
                 Like .open but append to it.
       .os       Output vertical distance that was saved by the sv request.
       .output string
                 Emit string directly to intermediate output, allowing leading
                 whitespace if string starts with " (which is stripped off).
       .pc       Reset page number character to ‘%’.
       .pc c     Page number character.
       .pev      Print the current environment and  each  defined  environment
                 state to stderr.
       .pi program
                 Pipe output to program (nroff only).
       .pl       Set  page  length to default 11i.  The current page length is
                 stored in register .p.
       .pl ±N    Change page length to ±N (default scaling indicator v).
       .pm       Print macro names and sizes (number of blocks of 128 bytes).
       .pm t     Print only total of sizes of  macros  (number  of  128  bytes
                 blocks).
       .pn ±N    Next page number N.
       .pnr      Print  the names and contents of all currently defined number
                 registers on stderr.
       .po       Change to previous page offset.  The current page  offset  is
                 available in register .o.
       .po ±N    Page offset N.
       .ps       Return to previous point size.
       .ps ±N    Point size; same as \s[±N].
       .psbb filename
                 Get the bounding box of a PostScript image filename.
       .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.
       .pvs      Change to previous post-vertical line spacing.
       .pvs ±N   Change  post-vertical  line  spacing according to ±N (default
                 scaling indicator p).
       .rchar c1 c2 ...
                 Remove the definitions of entities c1, c2, ...
       .rd prompt
                 Read insertion.
       .return   Return from a macro.
       .return anything
                 Return twice, namely from the macro at the current level  and
                 from the macro one level higher.
       .rfschar f c1 c2 ...
                 Remove the definitions of entities c1, c2, ... for font f.
       .rj n     Right justify the next n input lines.
       .rm name  Remove request, macro, or string name.
       .rn old new
                 Rename request, macro, or string old to new.
       .rnn reg1 reg2
                 Rename register reg1 to reg2.
       .rr register
                 Remove register.
       .rs       Restore spacing; turn no-space mode off.
       .rt ±N    Return  (upward only) to marked vertical place (default scal‐
                 ing indicator v).
       .schar c anything
                 Define global fallback character (or glyph) c as string  any‐
                 thing.
       .shc      Reset soft hyphen glyph to \(hy.
       .shc c    Set the soft hyphen glyph to c.
       .shift n  In a macro, shift the arguments by n positions.
       .sizes s1 s2 ... sn [0]
                 Set  available  font  sizes similar to the sizes command in a
                 DESC file.
       .so filename
                 Include source file.
       .sp       Skip one line vertically.
       .sp N     Space vertical distance N up or down according to sign  of  N
                 (default scaling indicator v).
       .special  Reset global list of special fonts to be empty.
       .special s1 s2 ...
                 Fonts  s1,  s2,  etc. are special and are searched for glyphs
                 not in the current font.
       .spreadwarn
                 Toggle the spread warning on and  off  without  changing  its
                 value.
       .spreadwarn limit
                 Emit  a warning if each space in an output line is widened by
                 limit or more (default scaling indicator m).
       .ss N     Set space glyph size to N/12 of the space width in  the  cur‐
                 rent font.
       .ss N M   Set  space  glyph size to N/12 and sentence space size set to
                 M/12 of the space width in the current font.
       .sty n style
                 Associate style with font position n.
       .substring xx n1 n2
                 Replace the string named xx with the substring defined by the
                 indices n1 and n2.
       .sv       Save 1 v of vertical space.
       .sv N     Save the vertical distance N for later output with os request
                 (default scaling indicator v).
       .sy command-line
                 Execute program command-line.
       .ta T N   Set tabs after  every  position  that  is  a  multiple  of  N
                 (default scaling indicator m).
       .ta n1 n2 ... nn T r1 r2 ... rn
                 Set  tabs  at  positions  n1,  n2,  ..., nn, then set tabs at
                 nn+r1, nn+r2, ..., nn+rn, then at  nn+rn+r1,  nn+rn+r2,  ...,
                 nn+rn+rn, and so on.
       .tc       Remove tab repetition glyph.
       .tc c     Set tab repetition glyph to c.
       .ti ±N    Temporary indent next line (default scaling indicator m).
       .tkf font s1 n1 s2 n2
                 Enable track kerning for font.
       .tl ’left’center’right’
                 Three-part title.
       .tm anything
                 Print anything on stdout.
       .tm1 anything
                 Print anything on stdout, allowing leading whitespace if any‐
                 thing starts with " (which is stripped off).
       .tmc anything
                 Similar to .tm1 without emitting a final newline.
       .tr abcd...
                 Translate a to b, c to d, etc. on output.
       .trf filename
                 Transparently output the contents of file filename.
       .trin abcd...
                 This is the same as the tr request except  that  the  asciify
                 request uses the character code (if any) before the character
                 translation.
       .trnt abcd...
                 This is the same as the tr request except that  the  transla‐
                 tions  do  not apply to text that is transparently throughput
                 into a diversion with \!.
       .troff    Make the built-in conditions t true and n false.
       .uf font  Set underline font to font (to be switched to by .ul).
       .ul N     Underline (italicize in troff) N input lines.
       .unformat diversion
                 Unformat space characters and tabs in  diversion,  preserving
                 font information.
       .vpt n    Enable vertical position traps if n is non-zero, disable them
                 otherwise.
       .vs       Change to previous vertical base line spacing.
       .vs ±N    Set vertical base line spacing to ±N (default scaling indica‐
                 tor p).
       .warn n   Set warnings code to n.
       .warnscale si
                 Set scaling indicator used in warnings to si.
       .wh N     Remove (first) trap at position N.
       .wh N trap
                 Set location trap; negative means from page bottom.
       .while cond anything
                 While condition cond is true, accept anything as input.
       .write stream anything
                 Write anything to the stream named stream.
       .writec stream anything
                 Similar to .write without emitting a final newline.
       .writem stream xx
                 Write  contents  of  macro  or  string xx to the stream named
                 stream.

       Besides these standard groff requests, there  might  be  further  macro
       calls.   They  can  originate  from a macro package (see roff(7) for an
       overview) or from a preprocessor.

       Preprocessor macros are easy to be recognized.  They enclose their code
       into a pair of characteristic macros.

       box, center, tab (@); c | c | c CfCB | CfCB | CfCB.  preprocessor@start
       macro@  end  macro  =  chem@.cstart@.cend  eqn@.EQ@.EN   gideal@.IS@.IE
       grap@.G1@.G2   grn@.GS@.GE   @@.IF   pic@.PS@.PE   refer@.R1@.R2   soe‐
       lim@none@none tbl@.TS@.TE _  glilypond@.lilypond  start@.lilypond  stop
       gperl@.Perl start@.Perl stop gpinyin@.pinyin start@.pinyin stop

       Note that the ‘ideal’ preprocessor is not available in groff yet.

ESCAPE SEQUENCES
       Escape  sequences are in-line language elements usually introduced by a
       backslash ‘\’ and followed  by  an  escape  name  and  sometimes  by  a
       required  argument.   Input  processing is continued directly after the
       escaped character or the argument (without  an  intervening  separation
       character).   So there must be a way to determine the end of the escape
       name and the end of the argument.

       This is done by enclosing names (escape name and  arguments  consisting
       of a variable name) by a pair of brackets [name] and constant arguments
       (number expressions and characters) by apostrophes  (ASCII  0x27)  like
       ’constant’.

       There  are  abbreviations  for short names.  Two-character escape names
       can be specified by an opening parenthesis like \(xy or \*(xy without a
       closing  counterpart.   And  all one-character names different from the
       special characters ‘[’ and ‘(’ can even be specified without a  marker,
       for example \nc or \$c.

       Constant  arguments  of  length 1 can omit the marker apostrophes, too,
       but there is no two-character analogue.

       While one-character escape sequences are mainly used for in-line  func‐
       tions  and  system related tasks, the two-letter names following the \(
       construct are glyphs predefined by the roff system;  these  are  called
       ‘Special Characters’ in the classical documentation.  Escapes sequences
       of the form \[name] denote glyphs too.

   Single-Character Escapes
       \"     Start of a comment.  Everything up to the end  of  the  line  is
              ignored.
       \#     Everything  up  to  and  including  the next newline is ignored.
              This is interpreted in copy mode.  This is like \"  except  that
              the terminating newline is ignored as well.
       \*s    The  string  stored  in  the  string variable with one-character
              name s.
       \*(st  The string stored in the string variable with two-character name
              st.
       \*[string]
              The  string stored in the string variable with name string (with
              arbitrary length).
       \*[stringvar arg1 arg2 ...]
              The string stored in the string variable with  arbitrarily  long
              name stringvar, taking arg1, arg2, ... as arguments.
       \$0    The  name  by  which  the  current  macro  was invoked.  The als
              request can make a macro have more than one name.
       \$x    Macro or string argument with one-digit number x in the range  1
              to 9.
       \$(xy  Macro  or  string argument with two-digit number xy (larger than
              zero).
       \$[nexp]
              Macro or string argument with  number  nexp,  where  nexp  is  a
              numerical expression evaluating to an integer ≥1.
       \$*    In  a  macro  or  string, the concatenation of all the arguments
              separated by spaces.
       \$@    In a macro or string, the concatenation  of  all  the  arguments
              with each surrounded by double quotes, and separated by spaces.
       \$^    In a macro, the representation of all parameters as if they were
              an argument to the ds request.
       \\     reduces to a single backslash; useful to delay  its  interpreta‐
              tion  as  escape  character in copy mode.  For a printable back‐
              slash, use \e, or even better \[rs], to be independent from  the
              current escape character.
       \´     The  acute accent ´; same as \(aa.  Unescaped: apostrophe, right
              quotation mark, single quote (ASCII 0x27).
       \`     The grave accent `; same as \(ga.  Unescaped: left quote,  back‐
              quote (ASCII 0x60).
       \-     The - (minus) sign in the current font.
       \_     The same as \(ul, the underline character.
       \.     The  same as a dot (‘.’).  Necessary in nested macro definitions
              so that ‘\\..’ expands to ‘..’.
       \%     Default optional hyphenation character.
       \!     Transparent line indicator.
       \?anything?
              In a diversion, this transparently embeds anything in the diver‐
              sion.   anything  is  read  in  copy  mode.  See also the escape
              sequences \!  and \?.
       \space Unpaddable space size space glyph (no line break).
       \0     Digit-width space.
       \|     1/6 em narrow space glyph; zero width in nroff.
       \^     1/12 em half-narrow space glyph; zero width in nroff.
       \&     Non-printable, zero-width glyph.
       \)     Like \& except that it behaves like a glyph  declared  with  the
              cflags request to be transparent for the purposes of end-of-sen‐
              tence recognition.
       \/     Increases the width of the preceding glyph so that  the  spacing
              between  that  glyph  and  the following glyph is correct if the
              following glyph is a roman glyph.
       \,     Modifies the spacing of the following glyph so that the  spacing
              between  that  glyph  and  the preceding glyph is correct if the
              preceding glyph is a roman glyph.
       \~     Unbreakable space that stretches like a normal inter-word  space
              when a line is adjusted.
       \:     Inserts  a  zero-width  break point (similar to \% but without a
              soft hyphen character).
       \newline
              Ignored newline, for continuation lines.
       \{     Begin conditional input.
       \}     End conditional input.
       \(sc   A glyph with two-character name sc; see section Special  Charac‐
              ters.
       \[name]
              A glyph with name name (of arbitrary length).
       \[comp1 comp2 ...]
              A composite glyph with components comp1, comp2, ...
       \a     Non-interpreted leader character.
       \A’anything’
              If  anything  is acceptable as a name of a string, macro, diver‐
              sion, register, environment or font it expands to 1,  and  to  0
              otherwise.
       \b’abc...’
              Bracket building function.
       \B’anything’
              If  anything  is  acceptable  as  a  valid numeric expression it
              expands to 1, and to 0 otherwise.
       \c     Interrupt text processing.
       \C’glyph’
              The glyph called glyph; same  as  \[glyph],  but  compatible  to
              other roff versions.
       \d     Forward (down) 1/2 em (1/2 line in nroff).
       \D’charseq’
              Draw  a  graphical element defined by the characters in charseq;
              see the groff info file for details.
       \e     Printable version of the current escape character.
       \E     Equivalent to an escape character, but  is  not  interpreted  in
              copy mode.
       \fF    Change to font with one-character name or one-digit number F.
       \fP    Switch back to previous font.
       \f(fo  Change to font with two-character name or two-digit number fo.
       \f[font]
              Change  to  font with arbitrarily long name or number expression
              font.
       \f[]   Switch back to previous font.
       \Ff    Change to font family with one-character name f.
       \F(fm  Change to font family with two-character name fm.
       \F[fam]
              Change to font family with arbitrarily long name fam.
       \F[]   Switch back to previous font family.
       \gr    Return format of register with one-character name r suitable for
              af request.
       \g(rg  Return  format  of  register with two-character name rg suitable
              for af request.
       \g[reg]
              Return format of register with arbitrarily long name  reg  suit‐
              able for af request.
       \h’N’  Local horizontal motion; move right N (left if negative).
       \H’N’  Set height of current font to N.
       \kr    Mark horizontal input place in one-character register r.
       \k(rg  Mark horizontal input place in two-character register rg.
       \k[reg]
              Mark  horizontal  input  place in register with arbitrarily long
              name reg.
       \l’Nc’ Horizontal line drawing function (optionally using character c).
       \L’Nc’ Vertical line drawing function (optionally using character c).
       \mc    Change to color with one-character name c.
       \m(cl  Change to color with two-character name cl.
       \m[color]
              Change to color with arbitrarily long name color.
       \m[]   Switch back to previous color.
       \Mc    Change filling color for closed drawn objects to color with one-
              character name c.
       \M(cl  Change filling color for closed drawn objects to color with two-
              character name cl.
       \M[color]
              Change filling color for closed  drawn  objects  to  color  with
              arbitrarily long name color.
       \M[]   Switch to previous fill color.
       \nr    The  numerical  value  stored  in the register variable with the
              one-character name r.
       \n(re  The numerical value stored in the  register  variable  with  the
              two-character name re.
       \n[reg]
              The  numerical  value stored in the register variable with arbi‐
              trarily long name reg.
       \N’n’  Typeset the glyph with index n in the current font.  No  special
              fonts  are  searched.   Useful  for adding (named) entities to a
              document using the char request and friends.
       \o’abc...’
              Overstrike glyphs a, b, c, etc.
       \O0    Disable glyph output.  Mainly for internal use.
       \O1    Enable glyph output.  Mainly for internal use.
       \p     Break and spread output line.
       \r     Reverse 1 em vertical motion (reverse line in nroff).
       \R’name ±n’
              The same as .nr name ±n.
       \s±N   Set/increase/decrease the point size to/by N scaled points; N is
              a one-digit number in the range 1 to 9.  Same as ps request.
       \s(±N
       \s±(N  Set/increase/decrease the point size to/by N scaled points; N is
              a two-digit number ≥1.  Same as ps request.
       \s[±N]
       \s±[N]
       \s’±N’
       \s±’N’ Set/increase/decrease the point  size  to/by  N  scaled  points.
              Same as ps request.
       \S’N’  Slant output by N degrees.
       \t     Non-interpreted horizontal tab.
       \u     Reverse (up) 1/2 em vertical motion (1/2 line in nroff).
       \v’N’  Local vertical motion; move down N (up if negative).
       \Ve    The  contents  of  the  environment  variable with one-character
              name e.
       \V(ev  The contents of the environment variable with two-character name
              ev.
       \V[env]
              The  contents  of the environment variable with arbitrarily long
              name env.
       \w’string’
              The width of the glyph sequence string.
       \x’N’  Extra line-space function (negative before, positive after).
       \X’string’
              Output string as device control function.
       \Yn    Output string variable or macro with one-character name n  unin‐
              terpreted as device control function.
       \Y(nm  Output string variable or macro with two-character name nm unin‐
              terpreted as device control function.
       \Y[name]
              Output string variable or macro with arbitrarily long name  name
              uninterpreted as device control function.
       \zc    Print c with zero width (without spacing).
       \Z’anything’
              Print  anything  and  then  restore  the horizontal and vertical
              position; anything may not contain tabs or leaders.

       The escape sequences \e, \., \", \$, \*, \a, \n, \t, \g,  and  \newline
       are interpreted in copy mode.

       Escape sequences starting with \( or \[ do not represent single charac‐
       ter escape sequences, but introduce escape names with two or more char‐
       acters.

       If  a  backslash  is followed by a character that does not constitute a
       defined escape sequence, the backslash  is  silently  ignored  and  the
       character maps to itself.

   Special Characters
       [Note:  ‘Special Characters’ is a misnomer; those entities are (output)
       glyphs, not (input) characters.]

       Common special characters are predefined by  escape  sequences  of  the
       form  \(xy  with  characters x and y.  In groff, it is also possible to
       use the writing \[xy] as well.

       Some of these special characters exist in the usual font while most  of
       them are only available in the special font.  Below you can see a small
       selection of the most important glyphs; a complete list can be found in
       groff_char(7).

              \(Do   Dollar $
              \(Eu   Euro €
              \(Po   British pound sterling £
              \(aq   Apostrophe quote '
              \(bu   Bullet sign ·
              \(co   Copyright ©
              \(cq   Single closing quote (right) ’
              \(ct   Cent ¢
              \(dd   Double dagger ‡
              \(de   Degree °
              \(dg   Dagger †
              \(dq   Double quote (ASCII 34) "
              \(em   Em-dash —
              \(en   En-dash –
              \(hy   Hyphen ‐
              \(lq   Double quote left “
              \(oq   Single opening quote (left) ‘
              \(rg   Registered sign ®
              \(rq   Double quote right ”
              \(rs   Printable backslash character \
              \(sc   Section sign §
              \(tm   Trademark symbol ™
              \(ul   Underline character _
              \(==   Identical ≡
              \(>=   Larger or equal ≥
              \(<=   Less or equal ≤
              \(!=   Not equal ≠
              \(->   Right arrow →
              \(<-   Left arrow ←
              \(+-   Plus-minus sign ±

   Unicode Characters
       There  is  the  extended  escape u that allows to include all available
       Unicode characters into some roff file.

       \[uxxxx]
              u is the escape name.  xxxx is a hexadecimal  number  of  4  hex
              digits, such as 0041 for the letter A, see \[u0041].

       \[uyyyyy]
              u  is  the  escape name.  yyyyy is a hexadecimal number of 5 hex
              digits, such as 2FA1A for a Chinese looking  character  for  CJK
              Compatibility Ideographs Supplement, see \[u2FA1A].

       Both  hexadecimal collections mean the corresponding Unicode code for a
       character.

       \[uhex1_hex2]
       \[uhex1_hex2_hex3]
              hex1, hex2, and hex3 are all Unicode hexadecimal codes (4  or  5
              hex  digits) that are used for overstriking, e.g.  \[u0041_0301]
              is A acute Á.

       The availability of the Unicode characters depends on  the  used  font.
       For  text mode, the device -Tutf8 is quite complete, for troff modes it
       might happen that some  or  many  characters  will  not  be  displayed.
       Please check your fonts.

   Strings
       Strings  are  defined  by the ds request and can be retrieved by the \*
       escape sequence.

       Strings share their name space with  macros.   So  strings  and  macros
       without  arguments  are  roughly  equivalent;  it is possible to call a
       string like a macro and vice-versa, but  this  often  leads  to  unpre‐
       dictable  results.   The following string is the only one predefined in
       groff.

       \*[.T]    The name of the current output device as specified by the  -T
                 command line option.

REGISTERS
       Registers  are  variables that store a value.  In groff, most registers
       store numerical values (see section NUMERICAL EXPRESSIONS  above),  but
       some can also hold a string value.

       Each  register is given a name.  Arbitrary registers can be defined and
       set with the nr request.

       The value stored in a register can be retrieved by the escape sequences
       introduced by \n.

       Most  useful  are  predefined registers.  In the following the notation
       name is used to refer to register name to  make  clear  that  we  speak
       about  registers.   Please keep in mind that the \n[] decoration is not
       part of the register name.

   Read-only Registers
       The following registers have predefined values that should not be modi‐
       fied  by  the  user  (usually,  registers starting with a dot are read-
       only).  Mostly, they provide information on  the  current  settings  or
       store results from request calls.

       \n[$$]    The process ID of troff.
       \n[.$]    Number of arguments in the current macro or string.
       \n[.a]    Post-line extra line-space most recently utilized using \x.
       \n[.A]    Set to 1 in troff if option -A is used; always 1 in nroff.
       \n[.b]    The emboldening offset while .bd is active.
       \n[.br]   Within  a  macro,  set to 1 if macro called with the ‘normal’
                 control character, and to 0 otherwise.
       \n[.c]    Current input line number.
       \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  environ‐
                 ment.   It  is  positive if the glyph extends above the base‐
                 line.
       \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[.d]    Current  vertical place in current diversion; equal to regis‐
                 ter nl.
       \n[.ev]   The name or number of the  current  environment  (string-val‐
                 ued).
       \n[.f]    Current font number.
       \n[.F]    The name of the current input file (string-valued).
       \n[.fam]  The current font family (string-valued).
       \n[.fn]   The current (internal) real font name (string-valued).
       \n[.fp]   The number of the next free font position.
       \n[.g]    Always  1 in GNU troff.  Macros should use it to test if run‐
                 ning under groff.
       \n[.h]    Text base-line high-water mark on current page or diversion.
       \n[.H]    Available horizontal resolution in basic units.
       \n[.height]
                 The current font height 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[.i]    Current indentation.
       \n[.in]   The indentation that applies to the current output line.
       \n[.int]  Positive if last output line contains \c.
       \n[.j]    The current adjustment mode.  It can be stored  and  used  to
                 set adjustment.  (n = 1, b = 1, l = 0, r = 5, c = 3).
       \n[.k]    The  current horizontal output position (relative to the cur‐
                 rent indentation).
       \n[.kern] 1 if pairwise kerning is enabled, 0 otherwise.
       \n[.l]    Current line length.
       \n[.L]    The current line spacing setting as set by .ls.
       \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 current drawing color (string-valued).
       \n[.M]    The current background color (string-valued).
       \n[.n]    Length of text portion on previous output line.
       \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
                 register .trunc.
       \n[.ns]   1 if in no-space mode, 0 otherwise.
       \n[.o]    Current page offset.
       \n[.O]    The suppression nesting level (see \O).
       \n[.p]    Current page length.
       \n[.P]    1 if the current page  is  being  printed,  0  otherwise  (as
                 determined by the -o command line option).
       \n[.pe]   1 during page ejection, 0 otherwise.
       \n[.pn]   The  number  of  the  next page: either the value set by a pn
                 request, or the number of the current page plus 1.
       \n[.ps]   The current point size in scaled points.
       \n[.psr]  The last-requested point size in scaled points.
       \n[.pvs]  The current post-vertical line spacing.
       \n[.R]    The number of unused number registers.  Always 10000  in  GNU
                 troff.
       \n[.rj]   The  number  of  lines to be right-justified as set by the rj
                 request.
       \n[.s]    Current point size as a decimal fraction.
       \n[.slant]
                 The slant of the current font as set with \S.
       \n[.sr]   The last requested point size in points as a decimal fraction
                 (string-valued).
       \n[.ss]   The  value of the parameters set by the first argument of the
                 ss request.
       \n[.sss]  The value of the parameters set by the second argument of the
                 ss request.
       \n[.sty]  The current font style (string-valued).
       \n[.t]    Vertical distance to the next trap.
       \n[.T]    Set to 1 if option -T is used.
       \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
                 .ne.  Useful in conjunction with the register .ne.
       \n[.u]    Equal to 1 in fill mode and 0 in no-fill mode.
       \n[.U]    Equal to 1 in safer mode and 0 in unsafe mode.
       \n[.v]    Current vertical line spacing.
       \n[.V]    Available vertical resolution in basic units.
       \n[.vpt]  1 if vertical position traps are enabled, 0 otherwise.
       \n[.w]    Width of previous glyph.
       \n[.warn] The  sum  of  the number codes of the currently enabled warn‐
                 ings.
       \n[.x]    The major version number.
       \n[.y]    The minor version number.
       \n[.Y]    The revision number of groff.
       \n[.z]    Name of current diversion.
       \n[.zoom] Zoom factor for current font (in multiples of 1/1000th;  zero
                 if no magnification).

   Writable Registers
       The following registers can be read and written by the user.  They have
       predefined default values, but these can be modified for customizing  a
       document.

       \n[%]     Current page number.
       \n[c.]    Current input line number.
       \n[ct]    Character type (set by width function \w).
       \n[dl]    Maximal width of last completed diversion.
       \n[dn]    Height of last completed diversion.
       \n[dw]    Current day of week (1–7).
       \n[dy]    Current day of month (1–31).
       \n[hours] The number of hours past midnight.  Initialized at start-up.
       \n[hp]    Current horizontal position at input line.
       \n[llx]   Lower  left  x-coordinate  (in  PostScript  units) of a given
                 PostScript image (set by .psbb).
       \n[lly]   Lower left y-coordinate (in  PostScript  units)  of  a  given
                 PostScript image (set by .psbb).
       \n[ln]    Output line number.
       \n[lsn]   The number of leading spaces of an input line.
       \n[lss]   The  horizontal  space corresponding to the leading spaces of
                 an input line.
       \n[minutes]
                 The number of minutes after the hour.  Initialized at  start-
                 up.
       \n[mo]    Current month (1–12).
       \n[nl]    Vertical position of last printed text base-line.
       \n[opmaxx]
       \n[opmaxy]
       \n[opminx]
       \n[opminy]
                 These  four registers mark the top left and bottom right hand
                 corners of a box which encompasses all written glyphs.   They
                 are reset to -1 by \O0 or \O1.
       \n[rsb]   Like register sb, but takes account of the heights and depths
                 of glyphs.
       \n[rst]   Like register st, but takes account of the heights and depths
                 of glyphs.
       \n[sb]    Depth  of string below base line (generated by width function
                 \w).
       \n[seconds]
                 The number of  seconds  after  the  minute.   Initialized  at
                 start-up.
       \n[skw]   Right  skip width from the center of the last glyph in the \w
                 argument.
       \n[slimit]
                 If greater than 0, the maximum number of objects on the input
                 stack.  If ≤0 there is no limit, i.e., recursion can continue
                 until virtual memory is exhausted.
       \n[ssc]   The amount  of  horizontal  space  (possibly  negative)  that
                 should  be added to the last glyph before a subscript (gener‐
                 ated by width function \w).
       \n[st]    Height of string above base line (generated by width function
                 \w).
       \n[systat]
                 The  return  value  of  the system() function executed by the
                 last sy request.
       \n[urx]   Upper right x-coordinate (in PostScript  units)  of  a  given
                 PostScript image (set by .psbb).
       \n[ury]   Upper  right  y-coordinate  (in  PostScript units) of a given
                 PostScript image (set by .psbb).
       \n[year]  The current year (year 2000 compliant).
       \n[yr]    Current year minus 1900.  For  Y2K  compliance  use  register
                 year instead.

UNDERLINING
       In  the  RUNOFF  language, the underlining was quite easy.  But in roff
       this is much more difficult.

   Underlining with .ul
       There exists a groff request .ul (see above)  that  can  underline  the
       next  or further source lines in nroff, but in troff it produces only a
       font change into italic.  So this request is not really useful.

   Underlining with .UL from ms
       In the ‘ms’ macro package in  tmac/s.tmac  groff_ms(7),  there  is  the
       macro .UL.  But this works only in troff, not in nroff.

   Underlining macro definitions
       So  one can use the italic nroff idea from .ul and the troff definition
       in ms for writing a useful new macro, something like
              .de UNDERLINE
              . ie n \\$1\f[I]\\$2\f[P]\\$3
              . el \\$1\Z'\\$2'\v'.25m'\D'l \w'\\$2'u 0'\v'-.25m'\[rs]\$3
              ..
       If doclifter (1) makes trouble, change the macro  name  UNDERLINE  into
       some  2-letter  word,  like  Ul.  Moreover change the font writing from
       \f[P] to \fP.

   Underlining without macro definitions
       If one does not want to use macro definitions, e.g. when doclifter gets
       lost, use the following:
              .ds u1 before
              .ds u2 in
              .ds u3 after
              .ie n \*[u1]\f[I]\*[u2]\f[P]\*[u3]
              .el \*[u1]\Z'\*[u2]'\v'.25m'\D'l \w'\*[u2]'u 0'\v'-.25m'\*[u3]
       Due  to doclifter, it might be necessary to change the variable writing
       \[xy] and \*[xy] into the strange ancient writing \*(xy and  \(xy,  and
       so on.

       Then these lines could look like
              .ds u1 before
              .ds u2 in
              .ds u3 after
              .ie n \*[u1]\fI\*(u2\fP\*(u3
              .el \*(u1\Z'\*(u2'\v'.25m'\D'l \w'\*(u2'u 0'\v'-.25m'\*(u3

       The result looks like
              before _i_n after

   Underlining with Overstriking \z and \(ul
       There is another possibility for underlining by using overstriking with
       \zc (print c with zero width without spacing) and \(ul (underline char‐
       acter).   This  produces  the underlining of 1 character, both in nroff
       and in troff.

       For example the underlining of a character say t looks like \z\[ul]t or
       \z\(ult

       Longer  words  look  then  a bit strange, but a useful mode is to write
       each character into a whole own line.  To underlines  the  3  character
       part "tar" of the word "start":
              before s\
              \z\[ul]t\
              \z\[ul]a\
              \z\[ul]r\
              t after
       or
              before s\
              \z\(ult\
              \z\(ula\
              \z\(ulr\
              t after

       The result looks like
              before s_t_a_rt after

COMPATIBILITY
       The  differences of the groff language in comparison to classical troff
       as defined by [CSTR #54] are documented in groff_diff(7).

       The groff system provides a compatibility mode, see groff(1) on how  to
       invoke this.

BUGS
       Report bugs to the groff bug mailing list ⟨bug-groff@gnu.org⟩.  Include
       a complete, self-contained example that will allow the bug to be repro‐
       duced, and say which version of groff you are using.


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


       box; cbp-1 | cbp-1 l | l .  ATTRIBUTE TYPE ATTRIBUTE VALUE = Availabil‐
       ity   text/groff = Stability Uncommitted


SEE ALSO
       The main source of information for the  groff  language  is  the  groff
       info(1) file.  Besides the gory details, it contains many examples.

       groff(1)
              the usage of the groff program and pointers to the documentation
              and availability of the groff system.

       groff_diff(7)
              the differences of the groff language as compared  to  classical
              roff.   This  is  the  authoritative document for the predefined
              language elements that are specific to groff.

       groff_char(7)
              the predefined groff special characters (glyphs).

       groff_font(5)
              the specification of fonts and the DESC file.

       roff(7)
              the history of roff, the common parts shared by  all  roff  sys‐
              tems, and pointers to further documentation.

       [CSTR #54]
              Nroff/Troff  User's  Manual  by  Ossanna  &  Kernighan  ⟨http://
              cm.bell-labs.com/cm/cs/cstr/54.ps.gz⟩ — the bible for  classical
              troff.

COPYING
       This file is part of groff, the GNU roff type-setting system.

       Copyright © 2000-2014 Free Software Foundation, Inc.

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

       A copy of the Free Documentation License is included as a  file  called
       FDL  in  the  main  directory  of the groff source package.  It is also
       available in the internet at ⟨http://www.gnu.org/copyleft/fdl.html⟩.

AUTHORS
       This   documentation   was   written   by    Bernd    Warken    ⟨groff-
       bernd.warken-72@web.de⟩  and  is  appended  and  maintained  by  Werner
       Lemberg ⟨wl@gnu.org⟩.



NOTES
       Source code for open source software components in Oracle  Solaris  can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-
       code-downloads.html.

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

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



Groff Version 1.22.3            4 November 2014                       GROFF(7)
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