Provided by: groff_1.21-7_amd64 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 behavior 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).  The special behavior can be delayed by using the \.  escape.
              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 behavior 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 I 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,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.
       .tl leftcenterright
                 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 │
                               ├─────────────┼─────────────┼────────────┤
                               │    eqn.EQ.EN     │
                               │    grap.G1.G2     │
                               │    grn.GS.GE     │
                               │    pic.PS.PE     │
                               │   refer.R1.R2     │
                               │   soelimnonenone    │
                               │    tbl.TS.TE     │
                               └─────────────┴─────────────┴────────────┘

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 \(ul, the underline character.
       \.     An uninterpreted dot (period), even at start of line.
       \%     Default optional hyphenation character.
       \!     Transparent line indicator.
       \?anything?
              In a diversion, this transparently embeds anything in the diversion.   anything  is
              read in copy mode.  See also the escape sequences \!  and \?.
       \space Unpaddable space size space glyph (no line break).
       \0     Digit-width space.
       \|     1/6 em narrow space glyph; zero width in nroff.
       \^     1/12 em half-narrow space glyph; zero width in nroff.
       \&     Non-printable, zero-width glyph.
       \)     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.
       \A’anything
              If anything is acceptable as a  name  of  a  string,  macro,  diversion,  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 suitable 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 arbitrarily 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 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).
       \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 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.   Some of these exist in the usual font while most of them are only
       available in the special font.  Below you can find  a  selection  of  the  most  important
       glyphs; a complete list can be found in groff_char(7).

              \(bu   Bullet sign
              \(co   Copyright
              \(ct   Cent
              \(dd   Double dagger
              \(de   Degree
              \(dg   Dagger
              \(rq   Printable double quote
              \(em   Em-dash
              \(hy   Hyphen
              \(rg   Registered sign
              \(rs   Printable backslash character
              \(sc   Section sign
              \(ul   Underline character
              \(==   Identical
              \(>=   Larger or equal
              \(<=   Less or equal
              \(!=   Not equal
              \(->   Right arrow
              \(<-   Left arrow
              \(+-   Plus-minus sign

   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 a 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.

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.

AUTHORS

       Copyright  (C)  2000,  2001,  2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software
       Foundation, Inc.

       This document is distributed under the terms of the FDL (GNU Free  Documentation  License)
       version  1.3  or  later.  You should have received a copy of the FDL on your system, it is
       also available on-line at the GNU copyleft site ⟨http://www.gnu.org/copyleft/fdl.html⟩.

       This document is part of groff, the GNU roff distribution.  It was written by Bernd Warken
       ⟨bwarken@mayn.de⟩; it is maintained by Werner Lemberg ⟨wl@gnu.org⟩.

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.