Provided by: groff_1.22.3-7_i386 bug

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
       background of the groff system.

       This  document  gives  only  short  descriptions of the predefined roff
       language 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
              precise, \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
       formatting 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
       herself 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
       counterpart.   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
       approximation 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 appropriate.

       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
              different 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
              separator  in  some functional escape sequences (but any pair of
              characters not part of the argument  do  work).   In  all  other
              positions,  it denotes the single quote or apostrophe character.
              Groff provides 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
              representation 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
              calculations.  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
              characters.   Continuation  lines can be specified by an escaped
              newline, 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
       values 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
       expressions:

              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-
       compatibility 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
       chosen  to  be  descriptive.   Only  the  following  denotations   need
       clarification.

              c         denotes a single character.
              font      a  font  either  specified  as  a  font name or a font
                        number.
              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
                 register macro until .. is encountered.
       .ami macro end
                 Append  to  a  macro  indirectly.   macro  and end are string
                 registers 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
                 components 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
                 indicator 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
                 environment.  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
                 indicator 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
                 indicator 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
                 scaling indicator v).
       .schar c anything
                 Define  global  fallback  character  (or  glyph)  c as string
                 anything.
       .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
                 current 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.
       .tlleftcenterright’
                 Three-part title.
       .tm anything
                 Print anything on stdout.
       .tm1 anything
                 Print anything on  stdout,  allowing  leading  whitespace  if
                 anything 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
                 translations 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
                 indicator 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.

                  ┌─────────────┬─────────────────┬────────────────┐
                  │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       │
                  │   soelimnonenone      │
                  │    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
       functions 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
              interpretation  as  escape  character  in  copy  mode.   For   a
              printable  backslash,  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,
              backquote (ASCII 0x60).
       \-     The - (minus) sign in the current font.
       \_     The same as \(ul, the underline character.
       \.     The same as a dot (‘.’).  Necessary in nested macro  definitions
              so that ‘\\..’ expands to ‘..’.
       \%     Default optional hyphenation character.
       \!     Transparent line indicator.
       \?anything?
              In  a  diversion,  this  transparently  embeds  anything  in the
              diversion.  anything is read in copy mode.  See also the  escape
              sequences \!  and \?.
       \space Unpaddable space size space glyph (no line break).
       \0     Digit-width space.
       \|     1/6 em narrow space glyph; zero width in nroff.
       \^     1/12 em half-narrow space glyph; zero width in nroff.
       \&     Non-printable, zero-width glyph.
       \)     Like  \&  except  that it behaves like a glyph declared with the
              cflags request to be transparent for  the  purposes  of  end-of-
              sentence 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
              Characters.
       \[name]
              A glyph with name name (of arbitrary length).
       \[comp1 comp2 ...]
              A composite glyph with components comp1, comp2, ...
       \a     Non-interpreted leader character.
       \Aanything’
              If anything  is  acceptable  as  a  name  of  a  string,  macro,
              diversion,  register,  environment  or font it expands to 1, and
              to 0 otherwise.
       \babc...’
              Bracket building function.
       \Banything’
              If anything is acceptable  as  a  valid  numeric  expression  it
              expands to 1, and to 0 otherwise.
       \c     Interrupt text processing.
       \Cglyph’
              The  glyph  called  glyph;  same  as \[glyph], but compatible to
              other roff versions.
       \d     Forward (down) 1/2 em (1/2 line in nroff).
       \Dcharseq’
              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
              suitable for af request.
       \hN’  Local horizontal motion; move right N (left if negative).
       \HN’  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.
       \lNc’ Horizontal line drawing function (optionally using character c).
       \LNc’ 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
              arbitrarily long name reg.
       \Nn’  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.
       \oabc...’
              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).
       \Rname n’
              The same as .nr name n.
       \sN   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]
       \sN\s±N’ Set/increase/decrease  the  point  size  to/by  N scaled points.
              Same as ps request.
       \SN’  Slant output by N degrees.
       \t     Non-interpreted horizontal tab.
       \u     Reverse (up) 1/2 em vertical motion (1/2 line in nroff).
       \vN’  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.
       \wstring’
              The width of the glyph sequence string.
       \xN’  Extra line-space function (negative before, positive after).
       \Xstring’
              Output string as device control function.
       \Yn    Output  string  variable  or  macro  with  one-character  name n
              uninterpreted as device control function.
       \Y(nm  Output string variable  or  macro  with  two-character  name  nm
              uninterpreted 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).
       \Zanything’
              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
       character escape sequences, but introduce escape names with two or more
       characters.

       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
       unpredictable 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
       modified 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
                 environment.  It is positive if the glyph extends  above  the
                 baseline.
       \n[.color]
                 1 if colors are enabled, 0 otherwise.
       \n[.csk]  The  skew of the last glyph added to the current environment.
                 The skew of a glyph is how far to the right of the center  of
                 a  glyph  the  center  of an accent over that glyph should be
                 placed.
       \n[.d]    Current  vertical  place  in  current  diversion;  equal   to
                 register nl.
       \n[.ev]   The  name  or  number  of  the  current  environment (string-
                 valued).
       \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
                 running 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
                 current 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
                 warnings.
       \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
                 (generated 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 in 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
       character).  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 start 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
       reproduced, and say which version of groff you are using.

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
              systems, 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⟩.