groff(7) — Linux manual page

Name | Description | groff Elements | Control Characters | Numerical Expressions | Conditions | Requests | Escape Sequences | Registers | Hyphenation | Underlining | Compatibility | Authors | See Also | COLOPHON

groff(7)              Miscellaneous Information Manual              groff(7)

Name         top

       groff - a short reference for the GNU roff language

Description         top

       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 provides only short descriptions of roff language
       elements.  Groff: The GNU Implementation of troff, by Trent A. Fisher
       and Werner Lemberg, is the primary groff manual, and is written in
       Texinfo.  You can browse it interactively with “info groff”.

       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.

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

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

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

              .command_name arg1 arg2

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

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

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

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

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

       2.     Double all backslashes.

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

       This does not produce the most efficient code, but it should work as
       a first measure.  For better strategies, see the groff Texinfo manual
       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         top

       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.  A few characters commonly seen on
       keyboards are treated specially by roff languages and may not look
       correct in output; they are the (double) quotation mark ("), the
       apostrophe ('), the hyphen-minus (-), the backslash (\), the caret or
       circumflex accent (^), the grave accent (`), and the tilde (~).  All
       are available if required; see groff_char(7).

       Moreover, there are some advanced roff elements.  A diversion stores
       (formatted) information into a macro for later usage.  See
       groff_tmac(5) for more details.  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
       Texinfo manual.

Control Characters         top

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

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

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

       '      The apostrophe 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 a single quote or apostrophe character,
              depending on the output device's glyph repertoire.  groff
              provides a printable representation with the \(aq escape
              sequence.

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

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

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

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

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

       space  Space characters separate arguments in requests, macros, and
              strings.  In text, they separate words.  When filling is
              enabled (the default), a line may be broken at a space.
              Further, in fill mode, multiple adjacent space characters
              cause groff to attempt end-of-sentence detection on the
              preceding word (and trailing punctuation).  The amount of
              space between sentences in fill mode is controlled by the ss
              request.  When adjustment is enabled, a space's width may be
              expanded to justify the line.  To get a space of definite
              width, use the escape sequences ‘\ ’ (this is the escape
              character followed by a space), \0, \|, \^, or \h; see section
              “Escape Sequences” below.  An adjustable but non-breaking
              space is available with \~.

       newline
              In text, newlines behave like space characters and trigger
              end-of-sentence recognition on the preceding text.
              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         top

       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
              s         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 Texinfo manual.

Conditions         top

       Conditions are expressions tested by the .if, .ie, and the .while
       requests.  The following table characterizes the different types of
       conditions.

              N         A numerical expression N yields true if its value is
                        greater than 0.
              !N        True if the value of N is ≤ 0 (see below).
              's1's2'   True if string s1 is identical to string s2.
              !'s1's2'  True if string s1 is not identical to string s2 (see
                        below).
              c g       True if a glyph g is available.
              d name    True if there is a string, macro, diversion, or
                        request called name.
              e         Current page number is even.
              F font    True if a font called font exists.
              m color   True if there is a color called color.
              n         Formatter is nroff.
              o         Current page number is odd.
              r reg     True if there is a number register called reg.
              S style   True if a style called style has been registered.
              t         Formatter is troff.
              v         Always false (for compatibilty with other troff
                        implementations).

       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         top

       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
       Texinfo manual and groff_diff(7) for all details.

       In the following request specifications, most argument names were
       chosen to be descriptive.  Only the following denotations need
       clarification.

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

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

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

   Request short reference
       .         Empty line, ignored.  Useful for structuring documents.
       .\" anything
                 Complete line is a comment.
       .ab string
                 Print string on standard error, exit program.
       .ad       Begin line adjustment for output lines in current adjust
                 mode.
       .ad c     Start line adjustment in mode c (c=l,r,c,b,n).
       .af register c
                 Assign format c to register (c=l,i,I,a,A).
       .aln new old
                 Create alias (additional name) new for existing number
                 register named old.
       .als new old
                 Create alias (additional name) new for existing request,
                 string, macro, or diversion old.
       .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
                 Write a backtrace of the input stack to the standard error
                 stream.  Also see the -b option of groff(1).
       .bd font N
                 Embolden font by N-1 units.
       .bd S font N
                 Embolden Special Font S when current font is font.
       .blm      Unset blank line macro (trap).  Restore default handling of
                 blank lines.
       .blm macro
                 Set blank line trap 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 output line; adjust if applicable.
       .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 n c1 c2 ...
                 Assign properties encoded by the number n to characters c1,
                 c2, and so on.
       .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 ...
                 Define a (character) class name comprising the characters
                 or range expressions c1, c2, and so on.
       .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.  See groff_tmac(5) for more details.
       .do name ...
                 Interpret the string, request, diversion, or macro name
                 (along with any arguments) with compatibility mode
                 disabled.  Note that compatibility mode is restored (if and
                 only if it was active) when the expansion of name is
                 interpreted.
       .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 \ or \.
       .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       Reset the hyphenation character to \% (the default).
       .hc char  Change the hyphenation character to char.
       .hcode c1 code1 [c2 code2] ...
                 Set the hyphenation code of character c1 to code1, that of
                 c2 to code2, and so on.
       .hla lang Set the hyphenation language to lang.
       .hlm n    Set the maximum number of consecutive hyphenated lines to
                 n.
       .hpf pattern-file
                 Read hyphenation patterns from pattern-file.
       .hpfa pattern-file
                 Append hyphenation patterns from pattern-file.
       .hpfcode a b [c d] ...
                 Define mapping values for character codes in pattern files
                 read with the .hpf and .hpfa requests.
       .hw word ...
                 Define how each word is to be hyphenated, with each hyphen
                 “-” indicating a hyphenation point.
       .hy       Set hyphenation mode to 1 (the default).
       .hy 0     Disable hyphenation; same as .nh.
       .hy mode  Set hyphenation mode to mode; see section “Hyphenation”
                 below.
       .hym      Set the (right) hyphenation margin to 0 (the default).
       .hym length
                 Set the (right) hyphenation margin to length (default
                 scaling indicator m).
       .hys      Set the hyphenation space to 0 (the default).
       .hys hyphenation-space
                 Suppress hyphenation of the line in adjustment modes “b” or
                 “n” if it can be justified by adding no more than
                 hyphenation-space extra space to each word space (default
                 scaling indicator m).
       .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 don't count lines interrupted with \c.
       .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, or in an
                 internal register used by .rt if no argument.
       .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       Disable hyphenation; same as “.hy 0”.
       .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       Report, to the standard error stream, the names and sizes
                 in bytes of defined macros, strings, and diversions.
       .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    Set/increase/decrease the point size to/by N scaled points
                 (a non-positive resulting point size is set to 1 u); also
                 see \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, diversion, or string name.
       .rn old new
                 Rename request, macro, diversion, or string old to new.
       .rnn reg1 reg2
                 Rename register reg1 to reg2.
       .rr ident Remove name of number register ident.
       .rs       Restore spacing; turn no-space mode off.
       .rt       Return (upward only) to vertical position marked by .mk on
                 the current page.
       .rt ±N    Return (upward only) to specified distance from the top of
                 the page (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 (the default) without
                 changing its value.
       .spreadwarn N
                 Emit a break warning if the additional space inserted for
                 each space between words in an output line adjusted to both
                 margins is larger than or equal to N.  A negative N is
                 treated as 0.  The default scaling indicator is m.  At
                 startup, .spreadwarn is inactive and N is 3 m.
       .ss N     Set minimal inter-word spacing to N 12ths of the space
                 width of the current font.
       .ss N M   As .ss N, and set additional inter-sentence spacing to
                 M 12ths of the space width of the current font.
       .stringdown stringvar
                 Replace each byte in the string named stringvar with its
                 lowercase version.
       .stringup stringvar
                 Replace each byte in the string named stringvar with its
                 uppercase version.
       .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+m×rn+r1 through nn+m×rn+rn, where m increments from 0,
                 1, 2, ... to infinity.
       .tc       Remove tab repetition glyph.
       .tc c     Set tab repetition glyph to c.
       .ti ±N    Temporary indent next line (default scaling indicator m).
       .tkf font s1 n1 s2 n2
                 Enable track kerning for font.
       .tl 'left'center'right'
                 Three-part title.
       .tm anything
                 Print anything on stderr.
       .tm1 anything
                 Print anything on stderr, 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     Enable all warnings.
       .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 recognize.  They enclose their code
       between a pair of characteristic macros.

                 ┌─────────────┬─────────────────┬────────────────┐
                 │preprocessor │   start macro   │    end macro   │
                 ├─────────────┼─────────────────┼────────────────┤
                 │    chem     .cstart     .cend      │
                 │    eqn      .EQ       .EN       │
                 │    grap     .G1       .G2       │
                 │    grn      .GS       .GE       │
                 │   ideal     .IS       .IE       │
                 │             │                 │      .IF       │
                 │    pic      .PS       .PE       │
                 │   refer     .R1       .R2       │
                 │   soelim    nonenone      │
                 │    tbl      .TS       .TE       │
                 ├─────────────┼─────────────────┼────────────────┤
                 │ glilypond   .lilypond start .lilypond stop │
                 │   gperl     .Perl start   .Perl stop   │
                 │  gpinyin    .pinyin start  .pinyin stop  │
                 └─────────────┴─────────────────┴────────────────┘
       Note that the ‘ideal’ preprocessor is not available in groff yet.

Escape Sequences         top

       Whereas requests must occur on control lines, escape sequences can
       occur intermixed with text and appear in arguments to requests and
       macros (and sometimes other escape sequences).  An escape sequence
       (or simply “escape”) is introduced by the escape character, a
       backslash “\” (but see the .ec request).  The next character
       identifies the escape's function.  Escapes vary in length.  Some take
       an argument, and of those, some have different syntactical forms for
       a one-character, two-character, or arbitrary-length argument.  Others
       accept only an arbitrary-length argument.  In the former convention,
       a one-character argument follows the function character immediately,
       an opening parenthesis “(” introduces a two-character argument, and
       an argument of arbitrary length is enclosed in brackets “[]”.  In the
       latter convention, the user selects a delimiter character other than
       “(” or “[]”—the neutral apostrophe “'” is a popular choice and used
       in this document.  A few escapes are idiosyncratic, and support both
       of the foregoing conventions (“\s”), designate their own terminating
       character (“\?”), consume input until the next newline (“\!”, “\"”,
       “\#”), or support an additional modifier character (“\s” again).
       Once an escape sequence terminates, input processing resumes with the
       next character.

       Escape sequences serve a variety of purposes.  Widespread uses
       include commenting the source document; changing the font style;
       setting the point size; interpolating special characters, number
       registers, and strings into the text; and placement or suppression of
       break and hyphenation points.  As with requests, use of escapes in
       source documents may interact poorly with a macro package you use;
       consult its documentation to learn of “safe” escapes or alternative
       facilities it provides to achieve the desired result.

   Escape short reference
       \"     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.
       \`     The grave accent `; same as \(ga.
       \-     The - (minus) sign in the current font.
       \_     The same as \(ul, the underline character.
       \.     The same as a dot (‘.’).  Necessary in nested macro
              definitions so that ‘\\..’ expands to ‘..’.
       \%     Default hyphenation character.
       \!     Transparent line indicator.
       \?anything?
              In a diversion, this transparently embeds anything in the
              diversion.  anything is read in copy mode.  See also the
              escape sequences \!  and \?.
       \space Unpaddable space size space glyph (no line break).
       \0     Digit-width unbreakable space.
       \|     1/6 em narrow unbreakable space glyph; zero width in nroff.
       \^     1/12 em half-narrow unbreakable space glyph; zero width in
              nroff.
       \&     Non-printable, zero-width glyph.
       \)     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” below.
       \[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     Continue output line at next input line.  Anything after this
              escape on the same line is ignored except \R (which works as
              usual).  Anything before \c on the same line is appended to
              the current partial output line.  The next non-command line
              after a line interrupted with \c counts as a new input line.
       \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 Texinfo manual 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 position in one-character register r.  r.
       \k(rg  Mark horizontal position in two-character register rg.
       \k[reg]
              Mark horizontal position 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 output line at next word boundary; adjust if applicable.
       \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
              must be a single digit; 0 restores the previous point size.
              (In compatibility mode only, a non-zero N must be in the range
              4–39.)  Otherwise, 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.  In groff, it is also possible to
       use the form \[xy].

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

              \(Do   Dollar $
              \(Eu   Euro 
              \(Po   British pound sterling £
              \(aq   Apostrophe quote '
              \(bu   Bullet sign ·
              \(co   Copyright ©
              \(cq   Single closing quote (right) 
              \(ct   Cent ¢
              \(dd   Double dagger 
              \(de   Degree sign °
              \(dg   Dagger 
              \(dq   Double quote "
              \(em   Em-dash 
              \(en   En-dash 
              \(ha   Caret/spacing circumflex accent (“hat”) ^
              \(hy   Hyphen 
              \(lq   Double quote left 
              \(oq   Single opening quote (left) 
              \(rg   Registered sign ®
              \(rq   Double quote right 
              \(rs   Reverse solidus/backslash \
              \(sc   Section sign §
              \(ti   Tilde (spacing) ~
              \(tm   Trademark symbol 
              \(ul   Underline character _
              \(==   Identical 
              \(>=   Larger or equal 
              \(<=   Less or equal 
              \(!=   Not equal 
              \(->   Right arrow 
              \(<-   Left arrow 
              \(+-   Plus-minus sign ±

   Unicode characters
       The extended escape u allows the inclusion of all available Unicode
       characters into a roff file.

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

       \[uyyyyy]
              u is the escape name.  yyyyy is a hexadecimal number of five
              hex digits, such as 2FA1A for a Chinese-looking character from
              the Unicode block CJK Compatibility Ideographs Supplement,
              thus \[u2FA1A].

       The hexadecimal value indicates the corresponding Unicode code point
       for a character.

       \[uhex1_hex2]
       \[uhex1_hex2_hex3]
              hex1, hex2, and hex3 are all Unicode hexadecimal codes (4 or 5
              hex digits) that are used for overstriking, e.g.,
              \[u0041_0301] is A acute, which can also be specified as Á;
              see groff_char(7).

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

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

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

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

Registers         top

       Registers are variables that store a value.  In groff, most registers
       store numerical values (see section “Numerical Expressions” above),
       but some can also hold a string value.

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

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

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

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

       \n[$$]    The process ID of troff.
       \n[.$]    Number of arguments in the current macro or string.
       \n[.a]    Post-line extra line-space most recently utilized using \x.
       \n[.A]    Set to 1 in troff if option -A is used; always 1 in nroff.
       \n[.b]    The emboldening offset while .bd is active.
       \n[.br]   Within a macro, set to 1 if macro called with the ‘normal’
                 control character, and to 0 otherwise.
       \n[.c]    Current input line number.
       \n[.C]    1 if compatibility mode is in effect, 0 otherwise.
                 Always 0 in a .do request; see register .cp below.
       \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[.cp]   Within a .do request, the saved value of compatibility mode
                 (see register .C above).
       \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]    Number of basic units per horizontal unit of output device
                 resolution.
       \n[.height]
                 The current font height as set with \H.
       \n[.hla]  The hyphenation language in the current environment.
       \n[.hlc]  The count of immediately preceding consecutive hyphenated
                 lines in the current environment.
       \n[.hlm]  The maximum number of consecutive hyphenated lines allowed
                 in the current environment.
       \n[.hy]   The hyphenation mode in the current environment.
       \n[.hym]  The hyphenation margin in the current environment.
       \n[.hys]  The hyphenation space adjustment threshold in the current
                 environment.
       \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]   Size of minimal inter-word spacing in twelfths of the space
                 width of the current font.
       \n[.sss]  Size of additional inter-sentence spacing in twelfths of
                 the space width of the current font.
       \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 an 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]    Number of basic units per vertical unit of output device
                 resolution.
       \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.

Hyphenation         top

       Several requests influence hyphenation.  Because conventions vary, a
       variety of hyphenation modes are available to the .hy request; these
       determine whether automatic hyphenation will apply to a word prior to
       breaking a line at the end of a column or page, and at which
       positions within that word hyphenation is permissible.  The default
       is “1” for historical reasons, but macro packages often override this
       default.

       0      disables hyphenation.

       1      enables hyphenation except after the first and before the last
              character of a word.

       2      disables hyphenation of the last word on a page or column.

       4      disables hyphenation before the last two characters of a word.

       8      disables hyphenation after the first two characters of a word.

       16     enables hyphenation before the last character of a word.

       32     enables hyphenation after the first character of a word.

       Note that any restrictions imposed by the hyphenation mode are not
       respected for words whose hyphenations have been explicitly specified
       with the hyphenation character (“\%” by default) or the .hw request.

       The nonzero values above are additive.  For example, value 12 causes
       groff to hyphenate neither the last two nor the first two characters
       of a word.  Note that value 13 would do exactly the same; in other
       words, value 1 need not be added if the value is larger than 1.

       Some values cannot be used together because they contradict; for
       instance, values 4 and 16, and values 8 and 32.

       The places within a word that are eligible for hyphenation are
       determined by language-specific data (.hla, .hpf, and .hpfa) and
       lettercase relationships (.hcode and .hpfcode).  Furthermore,
       hyphenation of a word might be suppressed because too many previous
       lines have been hyphenated (.hlm), the line has not reached a certain
       minimum length (.hym), or the line can instead be adjusted with up to
       a certain amount of additional inter-word space (.hys).  See
       groff_diff(7) or the groff Texinfo manual for further details.

Underlining         top

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

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

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

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

   Underlining without macro definitions
       If one does not want to use macro definitions, e.g., when doclifter
       gets lost, use the following:
              .ds u1 before
              .ds u2 in
              .ds u3 after
              .ie n \*[u1]\f[I]\*[u2]\f[P]\*[u3]
              .el \*[u1]\Z'\*[u2]'\v'.25m'\D'l \w'\*[u2]'u 0'\v'-.25m'\*[u3]
       When using doclifter, it might be necessary to change syntax forms
       such as \[xy] and \*[xy] to those supported by AT&T troff: \*(xy and
       \(xy, and so on.

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

       The result looks like
              before _i_n after

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

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

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

       The result looks like
              before s_t_a_rt after

Compatibility         top

       The differences between the groff language and 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.

Authors         top

       This document was written by Bernd Warken ⟨groff-bernd.warken-72@
       web.de⟩.

See Also         top

       Groff: The GNU Implementation of troff, by Trent A. Fisher and Werner
       Lemberg, is the primary groff manual.  You can browse it
       interactively with “info groff”.  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)
              describes the differences between the groff language and
              classical troff.

              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.

       groff_tmac(5)
              contains an overview of available groff macro packages,
              instructions on how to interface them with a document,
              guidance on writing macro packages and using diversions, and
              historical information on macro package naming conventions.

       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.

       Wikipedia
              article about groffhttps://en.wikipedia.org/wiki/Groff_%28software%29⟩.

       Tutorial about groff
              Manas Laha - An Introduction to the GNU Groff Text Processing
              System ⟨dl.dropbox.com/u/4299293/grofftut.pdf⟩

       troff.org
              This is a collection of internet sites with classical roff
              documentations and other information.

COLOPHON         top

       This page is part of the groff (GNU troff) project.  Information
       about the project can be found at 
       ⟨http://www.gnu.org/software/groff/⟩.  If you have a bug report for
       this manual page, see ⟨http://www.gnu.org/software/groff/⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2020-07-14.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-07-12.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to man-pages@man7.org

groff 1.22.4.234-3ba6           14 July 2020                        groff(7)

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