groff - a short reference for the GNU roff language
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 blanks
    from the command name and among themselves, for example,
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 will be 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 \[rs]\$1\$2 To be more
      precise, \[rs]\$1\$2 represents the current escape character. To
      get a backslash glyph, use \[rs]\$1\$2 or \[rs]\$1\$2
- 2.
- Double all backslashes.
- 3.
- Begin all text lines with the special non-spacing character
      \[rs]\$1\$2
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.
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
    \$* 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 \$* request and retrieved by the \[rs]\$1\$2 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
    \$* request and retrieved by the \[rs]\$1\$2 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 \$* request.
Fonts are identified either by a name or by an internal
    number. The current font is chosen by the \$* request or by the
    \[rs]\$1\$2 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 characters have a constant width
  anyway.
Moreover, there are some advanced roff elements. A
    diversion stores 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.
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 \$* \$* \$* and \$*
      There it is the control character that introduces a request (or macro).
      The special behavior can be delayed by using the \[rs]\$1\$2
      escape. By using the \$* 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 \$* 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 will work). In all other positions, it denotes the single quote
      or apostrophe character. Groff provides a printable representation with
      the \[rs]\$1\$2 escape sequence.
  - The double quote is used to enclose arguments in requests, macros,
    and
- strings. In the \$* and \$* requests, a leading double quote
      in the argument will be stripped off, making everything else afterwards
      the string to be defined (enabling leading whitespace). The escaped double
      quote \[rs]\$1\$2 introduces a comment. Otherwise, it is not
      special. Groff provides a printable representation with the
      \[rs]\$1\$2 escape sequence.
- The backslash usually introduces an escape sequence (this can be
- changed with the \$* request). A printed version of the escape
      character is the \[rs]\$1\$2 escape; a backslash glyph can be
      obtained by \[rs]\$1\$2
- 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), \[rs]\$1\$2 \[rs]\$1\$2 or
      \[rs]\$1\$2 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.
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 (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:
  - The maximum of
- e1 and e2.
- The minimum of
- e1 and e2.
- Evaluate
- e using c as the default scaling indicator.
 
For details see the groff info file.
Conditions occur in tests raised by the \$* \$* and the
  \$* 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.
- 's1's2'
- True if string s1 is identical to
    string s2.
- !'s1's2'
- True if string s1 is not identical to
      string s2.
- cch
- True if there is a character 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.
 
This section provides a short reference for the predefined requests. In groff,
  request and macro 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. An argument can be enclosed by a pair of double
    quotes. This is very handy if an argument contains space characters, e.g.,
    "arg with space" denotes a single argument.
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 \[rs]\$1\$2 and
      \[rs]\$1\$2
- 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 will be 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 will be 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.
Empty line, ignored. Useful for structuring documents. Complete line is a
  comment. Print string on standard error, exit program. Begin line
  adjustment for output lines in current adjust mode. Start line adjustment in
  mode c (c=l,r,b,n). Assign format
  c to register (c=l,i,I,a,A).
  Create alias name for register. Create alias name for request, string,
  macro, or diversion object. Append to macro until .. is
  encountered. Append to macro until \$* is called. Same as
  \$* but with compatibility mode switched off during macro expansion.
  Same as \$* but with compatibility mode switched off during macro
  expansion. Append to a macro whose name is contained in the string register
  macro until .. is encountered. Append to a macro indirectly.
  macro and end are string registers whose contents are
  interpolated for the macro name and the end macro, respectively. Same as
  \$* but with compatibility mode switched off during macro expansion.
  Same as \$* but with compatibility mode switched off during macro
  expansion. Append anything to stringvar. Same as \$* but
  with compatibility mode switched off during string expansion. Unformat ASCII
  characters, spaces, and some escape sequences in diversion. Print a
  backtrace of the input on stderr. Embolden font by N-1 units.
  Embolden Special Font S when current font is font. Unset the
  blank line macro. Set the blank line macro to macro. End current
  diversion. Divert to macro, omitting a partially filled line. End
  current diversion. Divert and append to macro, omitting a partially
  filled line. Eject current page and begin new page. Eject current page; next
  page number ±N. Line break. Break and spread output line. Same
  as \[rs]\$1\$2 Break out of a while loop. Reset no-break control
  character to Set no-break control character to c. Reset control
  character to Set control character to c. Center the next input line.
  Center following N input lines. Copy contents of file filename
  unprocessed to stdout or to the diversion. Treat characters c1,
  c2, ... according to mode number. Change trap
  location to N . Define character c as string anything.
  Chop the last character off macro, string, or diversion object. Close
  the stream. Enable colors. If N is zero disable colors,
  otherwise enable them. Map glyph name from to glyph name to
  while constructing a composite glyph name. Finish the current iteration of a
  while loop. Enable compatibility mode. If N is zero disable
  compatibility mode, otherwise enable it. Set constant character width mode for
  font to N/36 ems with em M. Continuous underline in
  nroff, like \$* in troff. End current diversion. Divert and append to
  macro. Define or redefine macro until .. is encountered.
  Define or redefine macro until \$* is called. Same as \$*
  but with compatibility mode switched off during macro expansion. Same as
  \$* but with compatibility mode switched off during macro expansion.
  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 \)\$*
  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. Define or redefine a macro whose name is contained in the
  string register macro until .. is encountered. 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. Same as \$* but with compatibility mode switched off
  during macro expansion. Same as \$* but with compatibility mode
  switched off during macro expansion. End current diversion. Divert to macro
  . Interpret \$* with compatibility mode disabled. Set
  stringvar to anything. Same as \$* but with compatibility
  mode switched off during string expansion. Set diversion trap to position
  N (default scaling indicator \)\$*
  Reset escape character to
  Set escape character to c. Restore escape
  character saved with \$* Save current escape character. Else part for
  if-else (\$* request. The macro will be run after the end of
  input. Turn off escape character mechanism. Switch to previous environment.
  Push down environment number or name env and switch to it. Copy the
  contents of environment env to the current environment. No pushing or
  popping. Exit from roff processing. Return to previous font family. Set the
  current font family to name. Disable field mechanism. Set field
  delimiter to a and pad character to space. Set field delimiter to
  a and pad character to b. Define fallback character c as
  string anything. Set fill color to previous fill color. Set fill color
  to c. Fill output lines. Flush output buffer. Mount font on
  position n. Mount font with long external name to short
  internal name on position n. Define fallback character c
  for font f as string anything. Reset list of special fonts for
  font to be empty. When the current font is font, then the fonts
  s1, s2, ... will be special. Return to previous font.
  Same as \$* or \$* Change to font name or number font;
  same as \)\$* escape sequence. Translate font1 to font2. Set
  glyph color to previous glyph color. Set glyph color to c. Remove
  additional hyphenation indicator character. Set up additional hyphenation
  indicator character c. Set the hyphenation code of character
  c1 to code1, that of c2 to code2, etc. Set the
  current hyphenation language to lang. Set the maximum number of
  consecutive hyphenated lines to n. Read hyphenation patterns from
  file. Append hyphenation patterns from file. Set input mapping
  for \$* List of words with exceptional hyphenation. Switch to
  hyphenation mode N. Set the hyphenation margin to n (default
  scaling indicator \)\$* Set
  the hyphenation space to n. If cond then anything
  else goto \$* If cond then anything; otherwise do
  nothing. Ignore text until .. is encountered. Ignore text until
  \$* Change to previous indent value. Change indent according to
  ±N (default scaling indicator \)\$*
   Set an input-line count trap for the
  next N lines. Same as \$* but count lines interrupted
  with \[rs]\$1\$2 as one line. Enable pairwise kerning. If n is
  zero, disable pairwise kerning, otherwise enable it. Remove leader repetition
  character. Set leader repetition character to c. Write the
  length of the string anything in register. Enable line-tabs mode
  (i.e., calculate tab positions relative to output line). If n is zero,
  disable line-tabs mode, otherwise enable it. Set input line number to
  N. Set input line number to N and filename to file.
  Ligature mode on if N>0. Change to previous line length. Set line
  length according to ±N (default size \)\$*
   default scaling
  indicator  \)\$*
   Change to the previous value of
  additional intra-line skip. Set additional intra-line
  skip value to N, i.e., N-1 blank lines are inserted after
  each text output line. Length of title (default scaling indicator \)\$*
  Margin character off.
  Print character c after each text line at
  actual distance from right margin. Set margin character to c and
  distance to N from right margin (default scaling indicator \)\$*
  Mark current vertical position
  in register. The same as the .so request except that file
  is searched in the tmac directories. No output-line adjusting. Need a one-line
  vertical space. Need N vertical space (default scaling
  indicator \)\$* No filling or
  adjusting of output-lines. No hyphenation.
  Number mode off. In line number mode,
  set number, multiple, spacing, and indent. Do not
  number next line. Do not number next N
  lines. Always execute anything. Define or modify register using
  ±N with auto-increment M. Make the built-in condition
  n true and t false. Turn no-space mode on. Immediately jump to
  end of current file. Next file. Open \)\$* \$* for writing and
  associate the stream named \)\$* \$* with it. Like \$* but
  append to it. Output vertical distance that was saved by the \$*
  request. Emit string directly to intermediate output, allowing leading
  whitespace if string starts with (which will be stripped off). Reset
  page number character to Page number character. Pipe output to
  program (nroff only). Set page length to default \)\$*
  The current page length is stored
  in \)\$* \$* Change page length to
  ±N (default scaling indicator \)\$*
   Print macro names and sizes (number
  of blocks of 128 bytes). Print only total of sizes of
  macros (number of 128 bytes blocks). Next page
  number N. Print the names and contents of all currently defined
  number registers on stderr. Change to previous page offset. The current page
  offset is available in \)\$* \$* Page offset N. Return to
  previous point-size. Point size; same as \)\$* Get the bounding box of a
  PostScript image filename. This behaves like the \$* request
  except that input comes from the standard output of command. Print the
  names and positions of all traps (not including input line traps and diversion
  traps) on stderr. Change to previous post-vertical line spacing. Change
  post-vertical line spacing according to ±N (default scaling
  indicator \)\$* Remove the
  definitions of characters c1, c2, ... Read
  insertion. Return from a macro. Return twice, namely from the macro at the
  current level and from the macro one level higher. Remove the definitions of
  characters c1, c2, ... for font f. Right justify
  the next n input lines. Remove request, macro, or string name.
  Rename request, macro, or string old to new. Rename register
  reg1 to reg2. Remove register. Restore spacing; turn
  no-space mode off. Return (upward only) to marked vertical place
  (default scaling indicator \)\$*
  Define global fallback
  character c as string anything. Reset soft hyphen
  character to \[rs]\$1\$2 Set the soft hyphen character to c. In
  a macro, shift the arguments by n positions. Set available font
  sizes similar to the sizes command in a DESC file. Include
  source file. Skip one line vertically. Space vertical distance N up or
  down according to sign of N (default scaling indicator \)\$*
  Reset global list of special fonts to
  be empty. Fonts s1, s2, etc. are
  special and will be searched for characters not in the current font. Toggle
  the spread warning on and off without changing its value. Emit a warning if
  each space in an output line is widened by limit or more (default
  scaling indicator \)\$*
  Space-character size set to
  N/12 of the spacewidth in the current font. Space-character size set to
  N/12 and sentence space size set to M/12 of the spacewidth in
  the current font (=1/3 em). Associate style
  with font position n. Replace the string named xx with the
  substring defined by the indices n1 and n2. Save \)\$*
  of vertical space.
  Save the vertical distance N for later output
  with \$* request. Execute program command-line. Set tabs after
  every position that is a multiple of N (default scaling
  indicator \)\$* 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. Remove tab repition character. Set
  tab repetition character to c. Temporary indent next line
  (default scaling indicator \)\$*
  Enable track kerning for
  font. Three-part title. Print anything on terminal (UNIX
  standard message output). Print anything on terminal (UNIX standard
  message output), allowing leading whitespace if anything starts with
  (which will be stripped off). Similar to \$* without emitting a final
  newline. Translate a to b, c to d, etc. on output.
  Transparently output the contents of file filename. This is the same as
  the \$* request except that the asciify request will use the
  character code (if any) before the character translation. This is the same as
  the \$* request except that the translations do not apply to text that
  is transparently throughput into a diversion with \[rs]\$1\$2 Make the
  built-in condition t true and n false. Underline font set to
  font (to be switched to by \$* Underline (italicize in troff)
  N input lines. Unformat space characters and tabs, preserving font
  information in diversion. Enable vertical position traps if n is
  non-zero, disable them otherwise. Change to previous vertical base line
  spacing. Set vertical base line spacing according to ±N (default
  scaling indicator \)\$*
  Default value is
  \)\$* Set
  warnings code to n. Set scaling indicator used in warnings to
  si. Remove (first) trap at position N. Set location trap;
  negative means from page bottom. While condition cond is true, accept
  anything as input. Write anything to the stream named
  stream. Similar to \$* without emitting a final newline. 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 | .PS | .PE | 
  
    | grap | .G1 | .G2 | 
  
    | grn | .GS | .GE | 
  
    | pic | .PS | .PE | 
  
    | refer | .R1 | .R2 | 
  
    | soelim | none | none | 
  
    | tbl | .TS | .TE | 
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
  resp. 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 \[rs]\$1\$2
    without a closing counterpart. And all one-character names different from
    the special characters and can even be specified without a marker in the
    form \[rs]\$1\$2
Constant arguments of length 1 can omit the marker
    apostrophes, too, but there is no two-character analogue.
While 1-character escape sequences are mainly used for in-line
    functions and system related tasks, the 2-letter names following the
    \[rs]\$1\$2 construct are used for special characters predefined by
    the roff system. Escapes sequences with names of more than two characters
    \)\$* denote user defined named characters (see the \$* request).
Beginning 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 \[rs]\$1\$2 except that the
  terminating newline is ignored as well. The string stored in the string
  variable with 1-character name s. The string stored in the string
  variable with 2-character name st. The string stored in the string
  variable with arbitrary length name stringvar, taking arg1,
  arg2, ... as arguments. The name by which the current macro was
  invoked. The \$* request can make a macro have more than one name.
  Macro or string argument with 1-place number x, where x is a
  digit between 1 and 9. Macro or string argument with 2-digit number xy.
  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. reduces to a single backslash; useful to
  delay its interpretation as escape character in copy mode. For a printable
  backslash, use \[rs]\$1\$2 or even better \[rs]\$1\$2 to be
  independent from the current escape character. The acute accent ´; same
  as \[rs]\$1\$2 Unescaped: apostrophe, right quotation mark, single
  quote (ASCII 0x27). The grave accent `; same as \[rs]\$1\$2 Unescaped:
  left quote, backquote (ASCII 0x60). The - sign in the current font. An
  uninterpreted dot (period), even at start of line. Default optional
  hyphenation character. Transparent line indicator. In a diversion, this will
  transparently embed anything in the diversion. anything is read
  in copy mode. See also the escape sequences \[rs]\$1\$2 and
  \[rs]\$1\$2 Unpaddable space-size space character (no line break).
  Digit width. 1/6 em narrow space character; zero width in nroff.
  1/12 em half-narrow space character; zero width in nroff.
  Non-printable, zero width character. Like \[rs]\$1\$2 except that it
  behaves like a character declared with the cflags request to be transparent
  for the purposes of end of sentence recognition. Increases the width of the
  preceding character so that the spacing between that character and the
  following character will be correct if the following character is a roman
  character. Modifies the spacing of the following character so that the spacing
  between that character and the preceding character will correct if the
  preceding character is a roman character. Unbreakable space that stretches
  like a normal inter-word space when a line is adjusted. Inserts a zero-width
  break point (similar to \[rs]\$1\$2 but without a soft hyphen
  character). Ignored newline, for continuation lines. Begin conditional input.
  End conditional input. The special character with 2-character name sc,
  see section Special Characters. The named character (or rather glyph)
  with arbitrary length name name. A composite glyph with components
  comp1, comp2, ... Non-interpreted leader character. If
  anything is acceptable as a name of a string, macro, diversion,
  register, environment or font it expands to 1, and to 0
  otherwise. Bracket building function. If anything is acceptable as a
  valid numeric expression it expands to 1, and to 0 otherwise.
  Interrupt text processing. The character called char; same as \)\$* but
  compatible to other roff versions. Forward (down) 1/2 em vertical unit (1/2
  line in nroff). Draw a graphical element defined by the characters in
  charseq; see groff info file for details. Printable version of the
  current escape character. Equivalent to an escape character, but is not
  interpreted in copy-mode. Change to font with 1-character name or 1-digit
  number F. Switch back to previous font. Change to font with 2-character
  name or 2-digit number fo. Change to font with arbitrary length name or
  number expression font. Switch back to previous font. Change to font
  family with 1-character name f. Change to font family with 2-character
  name fm. Change to font family with arbitrary length name fam.
  Switch back to previous font family. Return format of register with name
  reg suitable for \$* Alternative forms \)\$* and \)\$* Local
  horizontal motion; move right N (left if negative). Set height of
  current font to N. Mark horizontal input place in register with
  arbitrary length name reg. Alternative forms \)\$* and \)\$* Horizontal
  line drawing function (optionally using character c). Vertical line
  drawing function (optionally using character c). Change to color
  color. Alternative forms \)\$* and \)\$* Switch back to previous color.
  Change filling color for closed drawn objects to color color.
  Alternative forms \)\$* and \)\$* Switch to previous fill color. The numerical
  value stored in the register variable with the 1-character name r. The
  numerical value stored in the register variable with the 2-character name
  re. The numerical value stored in the register variable with arbitrary
  length name reg. Typeset the character with code n in the
  current font, no special fonts are searched. Useful for adding characters to a
  font using the \$* request. Overstrike characters a, b,
  c, etc. Disable glyph output. Mainly for internal use. Enable glyph
  output. Mainly for internal use. Break and spread output line. Reverse
  1 em vertical motion (reverse line in nroff). The same as \$*
  name ±n. Set the point size to N scaled points.
  Note the alternative forms \s±[N],
  \s'±N'\)\$*
  \s±'N'\)\$* \)\$* \)\$*
  \s±(xy\)\$* \)\$* Same as \$*
  request. Slant output N degrees. Non-interpreted horizontal tab.
  Reverse (up) 1/2 em vertical motion (1/2 line in nroff). Local vertical
  motion; move down N (up if negative). The contents of the environment
  variable env. Alternative forms \)\$* and \)\$* The width of the
  character sequence string. Extra line-space function (negative before,
  positive after). Output string as device control function. Output
  string variable or macro name uninterpreted as device control function.
  Alternative forms \)\$* and \)\$* Print c with zero width (without
  spacing). Print anything and then restore the horizontal and vertical
  position; anything may not contain tabs or leaders.
The escape sequences \[rs]\$1\$2 \[rs]\$1\$2
    \[rs]\$1\$2 \[rs]\$1\$2 \[rs]\$1\$2 \[rs]\$1\$2
    \[rs]\$1\$2 \[rs]\$1\$2 \[rs]\$1\$2 and \)\$* are
    interpreted in copy mode.
Escape sequences starting with \[rs]\$1\$2 or
    \[rs]\$1\$2 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.
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'll find a selection of the most important glyphs; a complete list
  can be found in groff_char(7).
Bullet sign Copyright Cent Double dagger Degree Dagger Printable
    double quote Em-dash Hyphen Registered sign Printable backslash character
    Section sign Underline character Identical Larger or equal Less or equal Not
    equal Right arrow Left arrow Plus-minus sign
 
Strings are defined by the \$* request and can be retrieved by the
  \[rs]\$1\$2 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 strings are predefined in groff.
  - The name of the current output device as specified by the
- \)\$* command line option.
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 request \$* register.
The value stored in a register can be retrieved by the escape
    sequences introduced by \[rs]\$1\$2
Most useful are predefined registers. In the following the
    notation name is used to refer to a register called \)\$* \$*
    to make clear that we speak about registers. Please keep in mind that the
    \)\$* decoration is not part of the register name.
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.
  - Number of arguments in the current macro or string.
- Post-line extra line-space most recently utilized using
- \)\$*
- Set to 1 in
- troff if option -A is used; always 1 in
    nroff.
- Current input line number.
- 1 if compatibility mode is in effect, 0 otherwise.
- The depth of the last character added to the current environment.
- It is positive if the character extends below the baseline.
- The number of lines remaining to be centered, as set by the
- \$* request.
- The height of the last character added to the current environment.
- It is positive if the character extends above the baseline.
- 1 if colors are enabled, 0 otherwise.
- The skew of the last character added to the current environment.
- The skew of a character is how far to the right of the center of a
      character the center of an accent over that character should be
    placed.
- Current vertical place in current diversion; equal to
- \)\$* \$*
- The name or number of the current environment (string-valued).
- Current font number.
- The current font family (string-valued).
- The current (internal) real font name (string-valued).
- The number of the next free font position.
- Always 1 in GNU troff.
- Macros should use it to test if running under groff.
- Text base-line high-water mark on current page or diversion.
- Available horizontal resolution in basic units.
- The current font height as set with
- \$*
- The current hyphenation language as set by the
- .hla request.
- The number of immediately preceding consecutive hyphenated lines.
- The maximum allowed number of consecutive hyphenated lines, as set by
- the \$* request.
- The current hyphenation flags (as set by the
- \$* request).
- The current hyphenation margin (as set by the
- \$* request).
- The current hyphenation space (as set by the
- \$* request).
- Current ident.
- The indent that applies to the current output line.
- Positive if last output line contains
- \[rs]\$1\$2
- 1 if pairwise kerning is enabled, 0 otherwise.
- Current line length.
- The current ligature mode (as set by the
- \$* request).
- The current line-tabs mode (as set by the
- \$* request).
- The line length that applies to the current output line.
- The title length (as set by the
- \$* request).
- The current drawing color (string-valued).
- The current background color (string-valued).
- Length of text portion on previous output line.
- The amount of space that was needed in the last
- \$* request that caused a trap to be sprung. Useful in conjunction
      with \)\$* \$*
- 1 if in no-space mode, 0 otherwise.
- Current page offset.
- Current page length.
- 1 during page ejection, 0 otherwise.
- The number of the next page: either the value set by a
- \$* request, or the number of the current page plus 1.
- The current pointsize in scaled points.
- The last-requested pointsize in scaled points.
- The current post-vertical line spacing.
- The number of lines to be right-justified as set by the rj request.
- Current point size as a decimal fraction.
- The slant of the current font as set with
- \$*
- The last requested pointsize in points as a decimal fraction
- (string-valued).
- The value of the parameters set by the first argument of the
- \$* request.
- The value of the parameters set by the second argument of the
- \$* request.
- The current font style (string-valued).
- Distance to the next trap.
- Set to 1
- if option -T is used.
- A string representation of the current tab settings suitable for use
- as an argument to the \$* request.
- The amount of vertical space truncated by the most recently sprung
- vertical position trap, or, if the trap was sprung by a \$*
      request, minus the amount of vertical motion produced by \$* In
      other words, at the point a trap is sprung, it represents the difference
      of what the vertical position would have been but for the trap, and what
      the vertical position actually is. Useful in conjunction with the \)\$*
      \$*
- Equal to 1 in fill mode and 0 in nofill mode.
- Equal to 1 in safer mode and 0 in unsafe mode.
- Current vertical line spacing.
- Available vertical resolution in basic units.
- 1  if vertical position traps are enabled, 0 otherwise.
- Width of previous character.
- The sum of the number codes of the currently enabled warnings.
- The major version number.
- The minor version number.
- The revision number of groff.
- Name of current diversion.
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.
  - Current page number.
- Current input line number.
- Character type (set by width function
- \[rs]\$1\$2
- Maximal width of last completed diversion.
- Height of last completed diversion.
- Current day of week (1-7).
- Current day of month (1-31).
- The number of hours past midnight.
- Initialized at start-up.
- Current horizontal position at input line.
- Lower left x-coordinate (in PostScript units) of a given PostScript
- image (set by \$*
- Lower left y-coordinate (in PostScript units) of a given PostScript
- image (set by \$*
- Output line number.
- The number of minutes after the hour.
- Initialized at start-up.
- Current month (1-12).
- Vertical position of last printed text base-line.
- Like
- \)\$* \$* but takes account of the heights and depths of
      characters.
- Like
- \)\$* \$* but takes account of the heights and depths of
      characters.
- Depth of string below base line (generated by width function
- \[rs]\$1\$2
- The number of seconds after the minute.
- Initialized at start-up.
- Right skip width from the center of the last character in the
- \[rs]\$1\$2 argument.
- 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.
- The amount of horizontal space (possibly negative) that should be
- added to the last character before a subscript (generated by width
      function \[rs]\$1\$2
- Height of string above base line (generated by width function
- \[rs]\$1\$2
- The return value of the
- system() function executed by the last \$* request.
- Upper right x-coordinate (in PostScript units) of a given PostScript
- image (set by \$*
- Upper right y-coordinate (in PostScript units) of a given PostScript
- image (set by \$*
- The current year (year 2000 compliant).
- Current year minus 1900.
- For Y2K compliance use \)\$* \$* instead.
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.
Report bugs to the Include a complete, self-contained example that will allow
  the bug to be reproduced, and say which version of groff you are using.
Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
This document is distributed under the terms of the FDL (GNU Free
    Documentation License) version 1.1 or later. You should have received a copy
    of the FDL on your system, it is also available on-line at the
This document is part of groff, the GNU roff distribution.
    It was written by it is maintained by
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 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]
- — the bible for classical troff.