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version 1.4, 2010/05/17 02:01:05 version 1.91, 2017/06/14 19:39:18
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 .\"     $Id$  .\"     $Id$
 .\"  .\"
 .\" Copyright (c) 2010 Kristaps Dzonsons <kristaps@bsd.lv>  .\" Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
   .\" Copyright (c) 2010,2011,2013-2015,2017 Ingo Schwarze <schwarze@openbsd.org>
 .\"  .\"
 .\" Permission to use, copy, modify, and distribute this software for any  .\" Permission to use, copy, modify, and distribute this software for any
 .\" purpose with or without fee is hereby granted, provided that the above  .\" purpose with or without fee is hereby granted, provided that the above
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 .Os  .Os
 .Sh NAME  .Sh NAME
 .Nm roff  .Nm roff
 .Nd roff language reference  .Nd roff language reference for mandoc
 .Sh DESCRIPTION  .Sh DESCRIPTION
 The  The
 .Nm roff  .Nm roff
 language is a general-purpose text-formatting language.  The purpose of  language is a general purpose text formatting language.
 this document is to consistently describe those language constructs  Since traditional implementations of the
 accepted by the  .Xr mdoc 7
   and
   .Xr man 7
   manual formatting languages are based on it,
   many real-world manuals use small numbers of
   .Nm
   requests and escape sequences intermixed with their
   .Xr mdoc 7
   or
   .Xr man 7
   code.
   To properly format such manuals, the
 .Xr mandoc 1  .Xr mandoc 1
 utility.  It is a work in progress.  utility supports a tiny subset of
   .Nm
   requests and escapes.
   Only these requests and escapes supported by
   .Xr mandoc 1
   are documented in the present manual,
   together with the basic language syntax shared by
   .Nm ,
   .Xr mdoc 7 ,
   and
   .Xr man 7 .
   For complete
   .Nm
   manuals, consult the
   .Sx SEE ALSO
   section.
 .Pp  .Pp
 An  Input lines beginning with the control character
   .Sq \&.
   are parsed for requests and macros.
   Such lines are called
   .Dq request lines
   or
   .Dq macro lines ,
   respectively.
   Requests change the processing state and manipulate the formatting;
   some macros also define the document structure and produce formatted
   output.
   The single quote
   .Pq Qq \(aq
   is accepted as an alternative control character,
   treated by
   .Xr mandoc 1
   just like
   .Ql \&.
   .Pp
   Lines not beginning with control characters are called
   .Dq text lines .
   They provide free-form text to be printed; the formatting of the text
   depends on the respective processing context.
   .Sh LANGUAGE SYNTAX
 .Nm  .Nm
 document follows simple rules:  lines beginning with the control  documents may contain only graphable 7-bit ASCII characters, the space
 characters  character, and, in certain circumstances, the tab character.
 .Sq \.  The backslash character
   .Sq \e
   indicates the start of an escape sequence, used for example for
   .Sx Comments ,
   .Sx Special Characters ,
   .Sx Predefined Strings ,
   and
   user-defined strings defined using the
   .Sx ds
   request.
   For a listing of escape sequences, consult the
   .Sx ESCAPE SEQUENCE REFERENCE
   below.
   .Ss Comments
   Text following an escaped double-quote
   .Sq \e\(dq ,
   whether in a request, macro, or text line, is ignored to the end of the line.
   A request line beginning with a control character and comment escape
   .Sq \&.\e\(dq
   is also ignored.
   Furthermore, request lines with only a control character and optional
   trailing whitespace are stripped from input.
   .Pp
   Examples:
   .Bd -literal -offset indent -compact
   \&.\e\(dq This is a comment line.
   \&.\e\(dq The next line is ignored:
   \&.
   \&.Sh EXAMPLES \e\(dq This is a comment, too.
   \&example text \e\(dq And so is this.
   .Ed
   .Ss Special Characters
   Special characters are used to encode special glyphs and are rendered
   differently across output media.
   They may occur in request, macro, and text lines.
   Sequences begin with the escape character
   .Sq \e
   followed by either an open-parenthesis
   .Sq \&(
   for two-character sequences; an open-bracket
   .Sq \&[
   for n-character sequences (terminated at a close-bracket
   .Sq \&] ) ;
   or a single one character sequence.
   .Pp
   Examples:
   .Bl -tag -width Ds -offset indent -compact
   .It Li \e(em
   Two-letter em dash escape.
   .It Li \ee
   One-letter backslash escape.
   .El
   .Pp
   See
   .Xr mandoc_char 7
   for a complete list.
   .Ss Text Decoration
   Terms may be text-decorated using the
   .Sq \ef
   escape followed by an indicator: B (bold), I (italic), R (regular), or P
   (revert to previous mode).
   A numerical representation 3, 2, or 1 (bold, italic, and regular,
   respectively) may be used instead.
   The indicator or numerical representative may be preceded by C
   (constant-width), which is ignored.
   .Pp
   The two-character indicator
   .Sq BI
   requests a font that is both bold and italic.
   It may not be portable to old roff implementations.
   .Pp
   Examples:
   .Bl -tag -width Ds -offset indent -compact
   .It Li \efBbold\efR
   Write in \fBbold\fP, then switch to regular font mode.
   .It Li \efIitalic\efP
   Write in \fIitalic\fP, then return to previous font mode.
   .It Li \ef(BIbold italic\efP
   Write in \f(BIbold italic\fP, then return to previous font mode.
   .El
   .Pp
   Text decoration is
   .Em not
   recommended for
   .Xr mdoc 7 ,
   which encourages semantic annotation.
   .Ss Predefined Strings
   Predefined strings, like
   .Sx Special Characters ,
   mark special output glyphs.
   Predefined strings are escaped with the slash-asterisk,
   .Sq \e* :
   single-character
   .Sq \e*X ,
   two-character
   .Sq \e*(XX ,
   and N-character
   .Sq \e*[N] .
   .Pp
   Examples:
   .Bl -tag -width Ds -offset indent -compact
   .It Li \e*(Am
   Two-letter ampersand predefined string.
   .It Li \e*q
   One-letter double-quote predefined string.
   .El
   .Pp
   Predefined strings are not recommended for use,
   as they differ across implementations.
   Those supported by
   .Xr mandoc 1
   are listed in
   .Xr mandoc_char 7 .
   Manuals using these predefined strings are almost certainly not portable.
   .Ss Whitespace
   Whitespace consists of the space character.
   In text lines, whitespace is preserved within a line.
   In request and macro lines, whitespace delimits arguments and is discarded.
   .Pp
   Unescaped trailing spaces are stripped from text line input unless in a
   literal context.
   In general, trailing whitespace on any input line is discouraged for
   reasons of portability.
   In the rare case that a blank character is needed at the end of an
   input line, it may be forced by
   .Sq \e\ \e& .
   .Pp
   Literal space characters can be produced in the output
   using escape sequences.
   In macro lines, they can also be included in arguments using quotation; see
   .Sx MACRO SYNTAX
   for details.
   .Pp
   Blank text lines, which may include whitespace, are only permitted
   within literal contexts.
   If the first character of a text line is a space, that line is printed
   with a leading newline.
   .Ss Scaling Widths
   Many requests and macros support scaled widths for their arguments.
   The syntax for a scaled width is
   .Sq Li [+-]?[0-9]*.[0-9]*[:unit:] ,
   where a decimal must be preceded or followed by at least one digit.
   Negative numbers, while accepted, are truncated to zero.
   .Pp
   The following scaling units are accepted:
   .Pp
   .Bl -tag -width Ds -offset indent -compact
   .It c
   centimetre
   .It i
   inch
   .It P
   pica (~1/6 inch)
   .It p
   point (~1/72 inch)
   .It f
   scale
   .Sq u
   by 65536
   .It v
   default vertical span
   .It m
   width of rendered
   .Sq m
   .Pq em
   character
   .It n
   width of rendered
   .Sq n
   .Pq en
   character
   .It u
   default horizontal span for the terminal
   .It M
   mini-em (~1/100 em)
   .El
   .Pp
   Using anything other than
   .Sq m ,
   .Sq n ,
 or  or
   .Sq v
   is necessarily non-portable across output media.
   See
   .Sx COMPATIBILITY .
   .Pp
   If a scaling unit is not provided, the numerical value is interpreted
   under the default rules of
   .Sq v
   for vertical spaces and
   .Sq u
   for horizontal ones.
   .Pp
   Examples:
   .Bl -tag -width ".Bl -tag -width 2i" -offset indent -compact
   .It Li \&.Bl -tag -width 2i
   two-inch tagged list indentation in
   .Xr mdoc 7
   .It Li \&.HP 2i
   two-inch tagged list indentation in
   .Xr man 7
   .It Li \&.sp 2v
   two vertical spaces
   .El
   .Ss Sentence Spacing
   Each sentence should terminate at the end of an input line.
   By doing this, a formatter will be able to apply the proper amount of
   spacing after the end of sentence (unescaped) period, exclamation mark,
   or question mark followed by zero or more non-sentence closing
   delimiters
   .Po
   .Sq \&) ,
   .Sq \&] ,
   .Sq \&' ,
   .Sq \&"
   .Pc .
   .Pp
   The proper spacing is also intelligently preserved if a sentence ends at
   the boundary of a macro line.
   .Pp
   Examples:
   .Bd -literal -offset indent -compact
   Do not end sentences mid-line like this.  Instead,
   end a sentence like this.
   A macro would end like this:
   \&.Xr mandoc 1 \&.
   .Ed
   .Sh REQUEST SYNTAX
   A request or macro line consists of:
   .Pp
   .Bl -enum -compact
   .It
   the control character
   .Sq \&.
   or
 .Sq \(aq  .Sq \(aq
 are parsed for macros.  Other lines are interpreted within the scope of  at the beginning of the line,
 prior macros:  .It
   optionally an arbitrary amount of whitespace,
   .It
   the name of the request or the macro, which is one word of arbitrary
   length, terminated by whitespace,
   .It
   and zero or more arguments delimited by whitespace.
   .El
   .Pp
   Thus, the following request lines are all equivalent:
 .Bd -literal -offset indent  .Bd -literal -offset indent
 \&.xx Macro lines change control state.  \&.ig end
 Other lines are interpreted within the current state.  \&.ig    end
   \&.   ig end
 .Ed  .Ed
 .Sh LANGUAGE SYNTAX  
 .Nm  
 documents may contain only graphable 7-bit ASCII characters, the space  
 character, and, in certain circumstances, the tab character.  All  
 manuals must have  
 .Ux  
 line terminators.  
 .Sh MACRO SYNTAX  .Sh MACRO SYNTAX
 Macros are arbitrary in length and begin with a control character ,  Macros are provided by the
 .Sq \.  .Xr mdoc 7
   and
   .Xr man 7
   languages and can be defined by the
   .Sx \&de
   request.
   When called, they follow the same syntax as requests, except that
   macro arguments may optionally be quoted by enclosing them
   in double quote characters
   .Pq Sq \(dq .
   Quoted text, even if it contains whitespace or would cause
   a macro invocation when unquoted, is always considered literal text.
   Inside quoted text, pairs of double quote characters
   .Pq Sq Qq
   resolve to single double quote characters.
   .Pp
   To be recognised as the beginning of a quoted argument, the opening
   quote character must be preceded by a space character.
   A quoted argument extends to the next double quote character that is not
   part of a pair, or to the end of the input line, whichever comes earlier.
   Leaving out the terminating double quote character at the end of the line
   is discouraged.
   For clarity, if more arguments follow on the same input line,
   it is recommended to follow the terminating double quote character
   by a space character; in case the next character after the terminating
   double quote character is anything else, it is regarded as the beginning
   of the next, unquoted argument.
   .Pp
   Both in quoted and unquoted arguments, pairs of backslashes
   .Pq Sq \e\e
   resolve to single backslashes.
   In unquoted arguments, space characters can alternatively be included
   by preceding them with a backslash
   .Pq Sq \e\~ ,
   but quoting is usually better for clarity.
   .Pp
   Examples:
   .Bl -tag -width Ds -offset indent -compact
   .It Li .Fn strlen \(dqconst char *s\(dq
   Group arguments
   .Qq const char *s
   into one function argument.
   If unspecified,
   .Qq const ,
   .Qq char ,
   and
   .Qq *s
   would be considered separate arguments.
   .It Li .Op \(dqFl a\(dq
   Consider
   .Qq \&Fl a
   as literal text instead of a flag macro.
   .El
   .Sh REQUEST REFERENCE
   The
   .Xr mandoc 1
   .Nm
   parser recognises the following requests.
   For requests marked as "ignored" or "unsupported", any arguments are
   ignored, and the number of arguments is not checked.
   .Bl -tag -width Ds
   .It Ic \&ab Op Ar message
   Abort processing.
   Currently unsupported.
   .It Ic \&ad Op Cm b | c | l | n | r
   Set line adjustment mode for subsequent text.
   Currently ignored.
   .It Ic \&af Ar registername format
   Assign an output format to a number register.
   Currently ignored.
   .It Ic \&aln Ar newname oldname
   Create an alias for a number register.
   Currently unsupported.
   .It Ic \&als Ar newname oldname
   Create an alias for a request, string, macro, or diversion.
   .It Ic \&am Ar macroname Op Ar endmacro
   Append to a macro definition.
   The syntax of this request is the same as that of
   .Ic \&de .
   .It Ic \&am1 Ar macroname Op Ar endmacro
   Append to a macro definition, switching roff compatibility mode off
   during macro execution (groff extension).
   The syntax of this request is the same as that of
   .Ic \&de1 .
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&am .
   .It Ic \&ami Ar macrostring Op Ar endstring
   Append to a macro definition, specifying the macro name indirectly
   (groff extension).
   The syntax of this request is the same as that of
   .Ic \&dei .
   .It Ic \&ami1 Ar macrostring Op Ar endstring
   Append to a macro definition, specifying the macro name indirectly
   and switching roff compatibility mode off during macro execution
   (groff extension).
   The syntax of this request is the same as that of
   .Ic \&dei1 .
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&ami .
   .It Ic \&as Ar stringname Op Ar string
   Append to a user-defined string.
   The syntax of this request is the same as that of
   .Sx \&ds .
   If a user-defined string with the specified name does not yet exist,
   it is set to the empty string before appending.
   .It Ic \&as1 Ar stringname Op Ar string
   Append to a user-defined string, switching roff compatibility mode off
   during macro execution (groff extension).
   The syntax of this request is the same as that of
   .Ic \&ds1 .
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&as .
   .It Ic \&asciify Ar divname
   Fully unformat a diversion.
   Currently unsupported.
   .It Ic \&backtrace
   Print a backtrace of the input stack.
   This is a groff extension and currently ignored.
   .It Ic \&bd Ar font Oo Ar curfont Oc Op Ar offset
   Artificially embolden by repeated printing with small shifts.
   Currently ignored.
   .It Ic \&bleedat Ar left top width height
   Set the BleedBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .It Ic \&blm Ar macroname
   Set a blank line trap.
   Currently unsupported.
   .It Ic \&box Ar divname
   Begin a diversion without including a partially filled line.
   Currently unsupported.
   .It Ic \&boxa Ar divname
   Add to a diversion without including a partially filled line.
   Currently unsupported.
   .It Ic \&bp Oo Cm + Ns | Ns Cm - Oc Ns Ar pagenumber
   Begin a new page.
   Currently ignored.
   .It Ic \&BP Ar source height width position offset flags label
   Define a frame and place a picture in it.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&br
   Break the output line.
   .It Ic \&break
   Break out of a
   .Ic \&while
   loop.
   Currently unsupported.
   .It Ic \&breakchar Ar char ...
   Optional line break characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&brnl Ar N
   Break output line after the next
   .Ar N
   input lines.
   This is a Heirloom extension and currently ignored.
   .It Ic \&brp
   Break and spread output line.
   Currently, this is implemented as an alias for
   .Ic \&br .
   .It Ic \&brpnl Ar N
   Break and spread output line after the next
   .Ar N
   input lines.
   This is a Heirloom extension and currently ignored.
   .It Ic \&c2 Op Ar char
   Change the no-break control character.
   Currently unsupported.
   .It Ic \&cc Op Ar char
   Change the control character.
   If
   .Ar char
   is not specified, the control character is reset to
   .Sq \&. .
   Trailing characters are ignored.
   .It Ic \&ce Op Ar N
   Center the next
   .Ar N
   input lines without filling.
   .Ar N
   defaults to 1.
   An argument of 0 or less ends centering.
   Currently, high level macros abort centering.
   .It Ic \&cf Ar filename
   Output the contents of a file.
   Ignored because insecure.
   .It Ic \&cflags Ar flags char ...
   Set character flags.
   This is a groff extension and currently ignored.
   .It Ic \&ch Ar macroname Op Ar dist
   Change a trap location.
   Currently ignored.
   .It Ic \&char Ar glyphname Op Ar string
   Define a new glyph.
   Currently unsupported.
   .It Ic \&chop Ar stringname
   Remove the last character from a macro, string, or diversion.
   Currently unsupported.
   .It Ic \&class Ar classname char ...
   Define a character class.
   This is a groff extension and currently ignored.
   .It Ic \&close Ar streamname
   Close an open file.
   Ignored because insecure.
   .It Ic \&CL Ar color text
   Print text in color.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&color Op Cm 1 | 0
   Activate or deactivate colors.
   This is a groff extension and currently ignored.
   .It Ic \&composite Ar from to
   Define a name component for composite glyph names.
   This is a groff extension and currently unsupported.
   .It Ic \&continue
   Immediately start the next iteration of a
   .Ic \&while
   loop.
   Currently unsupported.
   .It Ic \&cp Op Cm 1 | 0
   Switch
   .Nm
   compatibility mode on or off.
   Currently ignored.
   .It Ic \&cropat Ar left top width height
   Set the CropBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .It Ic \&cs Ar font Op Ar width Op Ar emsize
   Constant character spacing mode.
   Currently ignored.
   .It Ic \&cu Op Ar N
   Underline next
   .Ar N
   input lines including whitespace.
   Currently ignored.
   .It Ic \&da Ar divname
   Append to a diversion.
   Currently unsupported.
   .It Ic \&dch Ar macroname Op Ar dist
   Change a trap location in the current diversion.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&de Ar macroname Op Ar endmacro
   Define a
   .Nm
   macro.
   Its syntax can be either
   .Bd -literal -offset indent
   .Pf . Ic \&de Ar macroname
   .Ar definition
   \&..
   .Ed
   .Pp
 or  or
 .Sq \(aq ,  
 at the beginning of the line.  
 An arbitrary amount of whitespace may sit between the control character  
 and the macro name.  
 Thus, the following are equivalent:  
 .Bd -literal -offset indent  .Bd -literal -offset indent
 \&.if  .Pf . Ic \&de Ar macroname Ar endmacro
 \&.\ \ \ \&if  .Ar definition
   .Pf . Ar endmacro
 .Ed  .Ed
 .Sh REFERENCE  .Pp
 This section is a canonical reference of all macros, arranged  Both forms define or redefine the macro
 alphabetically.  .Ar macroname
 .Ss \&am  to represent the
 The syntax of this macro is the same as that of  .Ar definition ,
 .Sx \&ig ,  which may consist of one or more input lines, including the newline
 except that a leading argument must be specified.  characters terminating each line, optionally containing calls to
 It is ignored, as are its children.  .Nm
 .Ss \&ami  requests,
 The syntax of this macro is the same as that of  .Nm
 .Sx \&ig ,  macros or high-level macros like
 except that a leading argument must be specified.  .Xr man 7
 It is ignored, as are its children.  or
 .Ss \&am1  .Xr mdoc 7
 The syntax of this macro is the same as that of  macros, whichever applies to the document in question.
 .Sx \&ig ,  .Pp
 except that a leading argument must be specified.  Specifying a custom
 It is ignored, as are its children.  .Ar endmacro
 .Ss \&de  macro works in the same way as for
 The syntax of this macro is the same as that of  .Ic \&ig ;
 .Sx \&ig ,  namely, the call to
 except that a leading argument must be specified.  .Sq Pf . Ar endmacro
 It is ignored, as are its children.  first ends the
 .Ss \&dei  .Ar definition ,
 The syntax of this macro is the same as that of  and after that, it is also evaluated as a
 .Sx \&ig ,  .Nm
 except that a leading argument must be specified.  request or
 It is ignored, as are its children.  .Nm
 .Ss \&de1  macro, but not as a high-level macro.
 The syntax of this macro is the same as that of  .Pp
 .Sx \&ig ,  The macro can be invoked later using the syntax
 except that a leading argument must be specified.  .Pp
 It is ignored, as are its children.  .D1 Pf . Ar macroname Op Ar argument Op Ar argument ...
 .Ss \&if  .Pp
 Begins a conditional that always evaluates to false.  Regarding argument parsing, see
   .Sx MACRO SYNTAX
   above.
   .Pp
   The line invoking the macro will be replaced
   in the input stream by the
   .Ar definition ,
   replacing all occurrences of
   .No \e\e$ Ns Ar N ,
   where
   .Ar N
   is a digit, by the
   .Ar N Ns th Ar argument .
   For example,
   .Bd -literal -offset indent
   \&.de ZN
   \efI\e^\e\e$1\e^\efP\e\e$2
   \&..
   \&.ZN XtFree .
   .Ed
   .Pp
   produces
   .Pp
   .D1 \efI\e^XtFree\e^\efP.
   .Pp
   in the input stream, and thus in the output: \fI\^XtFree\^\fP.
   Each occurrence of \e\e$* is replaced with all the arguments,
   joined together with single blank characters.
   .Pp
   Since macros and user-defined strings share a common string table,
   defining a macro
   .Ar macroname
   clobbers the user-defined string
   .Ar macroname ,
   and the
   .Ar definition
   can also be printed using the
   .Sq \e*
   string interpolation syntax described below
   .Ic ds ,
   but this is rarely useful because every macro definition contains at least
   one explicit newline character.
   .Pp
   In order to prevent endless recursion, both groff and
   .Xr mandoc 1
   limit the stack depth for expanding macros and strings
   to a large, but finite number, and
   .Xr mandoc 1
   also limits the length of the expanded input line.
   Do not rely on the exact values of these limits.
   .It Ic \&de1 Ar macroname Op Ar endmacro
   Define a
   .Nm
   macro that will be executed with
   .Nm
   compatibility mode switched off during macro execution.
   This is a groff extension.
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&de .
   .It Ic \&defcolor Ar newname scheme component ...
   Define a color name.
   This is a groff extension and currently ignored.
   .It Ic \&dei Ar macrostring Op Ar endstring
   Define a
   .Nm
   macro, specifying the macro name indirectly (groff extension).
   The syntax of this request is the same as that of
   .Ic \&de .
   The effect is the same as:
   .Pp
   .D1 Pf . Cm \&de No \e* Ns Bo Ar macrostring Bc Op \e* Ns Bq Ar endstring
   .It Ic \&dei1 Ar macrostring Op Ar endstring
   Define a
   .Nm
   macro that will be executed with
   .Nm
   compatibility mode switched off during macro execution,
   specifying the macro name indirectly (groff extension).
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&dei .
   .It Ic \&device Ar string ...
   .It Ic \&devicem Ar stringname
   These two requests only make sense with the groff-specific intermediate
   output format and are unsupported.
   .It Ic \&di Ar divname
   Begin a diversion.
   Currently unsupported.
   .It Ic \&do Ar command Op Ar argument ...
   Execute
   .Nm
   request or macro line with compatibility mode disabled.
   Currently unsupported.
   .It Ic \&ds Ar stringname Op Oo \(dq Oc Ns Ar string
   Define a user-defined string.
   The
   .Ar stringname
   and
   .Ar string
   arguments are space-separated.
   If the
   .Ar string
   begins with a double-quote character, that character will not be part
   of the string.
   All remaining characters on the input line form the
   .Ar string ,
   including whitespace and double-quote characters, even trailing ones.
   .Pp
   The
   .Ar string
   can be interpolated into subsequent text by using
   .No \e* Ns Bq Ar stringname
   for a
   .Ar stringname
   of arbitrary length, or \e*(NN or \e*N if the length of
   .Ar stringname
   is two or one characters, respectively.
   Interpolation can be prevented by escaping the leading backslash;
   that is, an asterisk preceded by an even number of backslashes
   does not trigger string interpolation.
   .Pp
   Since user-defined strings and macros share a common string table,
   defining a string
   .Ar stringname
   clobbers the macro
   .Ar stringname ,
   and the
   .Ar stringname
   used for defining a string can also be invoked as a macro,
   in which case the following input line will be appended to the
   .Ar string ,
   forming a new input line passed to the
   .Nm
   parser.
   For example,
   .Bd -literal -offset indent
   \&.ds badidea .S
   \&.badidea
   H SYNOPSIS
   .Ed
   .Pp
   invokes the
   .Ic SH
   macro when used in a
   .Xr man 7
   document.
   Such abuse is of course strongly discouraged.
   .It Ic \&ds1 Ar stringname Op Oo \(dq Oc Ns Ar string
   Define a user-defined string that will be expanded with
   .Nm
   compatibility mode switched off during string expansion.
   This is a groff extension.
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Ic \&ds .
   .It Ic \&dwh Ar dist macroname
   Set a location trap in the current diversion.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&dt Op Ar dist macroname
   Set a trap within a diversion.
   Currently unsupported.
   .It Ic \&ec Op Ar char
   Enable the escape mechanism and change the escape character.
   The
   .Ar char
   argument defaults to the backslash
   .Pq Sq \e .
   .It Ic \&ecr
   Restore the escape character.
   Currently unsupported.
   .It Ic \&ecs
   Save the escape character.
   Currently unsupported.
   .It Ic \&el Ar body
   The
   .Dq else
   half of an if/else conditional.
   Pops a result off the stack of conditional evaluations pushed by
   .Ic \&ie
   and uses it as its conditional.
   If no stack entries are present (e.g., due to no prior
   .Ic \&ie
   calls)
   then false is assumed.
   The syntax of this request is similar to
   .Ic \&if
   except that the conditional is missing.
   .It Ic \&em Ar macroname
   Set a trap at the end of input.
   Currently unsupported.
   .It Ic \&EN
   End an equation block.
   See
   .Ic \&EQ .
   .It Ic \&eo
   Disable the escape mechanism completely.
   .It Ic \&EP
   End a picture started by
   .Ic \&BP .
   This is a Heirloom extension and currently unsupported.
   .It Ic \&EQ
   Begin an equation block.
   See
   .Xr eqn 7
   for a description of the equation language.
   .It Ic \&errprint Ar message
   Print a string like an error message.
   This is a Heirloom extension and currently ignored.
   .It Ic \&ev Op Ar envname
   Switch to another environment.
   Currently unsupported.
   .It Ic \&evc Op Ar envname
   Copy an environment into the current environment.
   Currently unsupported.
   .It Ic \&ex
   Abort processing and exit.
   Currently unsupported.
   .It Ic \&fallback Ar curfont font ...
   Select the fallback sequence for a font.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fam Op Ar familyname
   Change the font family.
   This is a groff extension and currently ignored.
   .It Ic \&fc Op Ar delimchar Op Ar padchar
   Define a delimiting and a padding character for fields.
   Currently unsupported.
   .It Ic \&fchar Ar glyphname Op Ar string
   Define a fallback glyph.
   Currently unsupported.
   .It Ic \&fcolor Ar colorname
   Set the fill color for \eD objects.
   This is a groff extension and currently ignored.
   .It Ic \&fdeferlig Ar font string ...
   Defer ligature building.
   This is a Heirloom extension and currently ignored.
   .It Ic \&feature Cm + Ns | Ns Cm - Ns Ar name
   Enable or disable an OpenType feature.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fi
   Switch to fill mode.
   See
   .Xr man 7 .
   Ignored in
   .Xr mdoc 7 .
   .It Ic \&fkern Ar font minkern
   Control the use of kerning tables for a font.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fl
   Flush output.
   Currently ignored.
   .It Ic \&flig Ar font string char ...
   Define ligatures.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fp Ar position font Op Ar filename
   Assign font position.
   Currently ignored.
   .It Ic \&fps Ar mapname ...
   Mount a font with a special character map.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fschar Ar font glyphname Op Ar string
   Define a font-specific fallback glyph.
   This is a groff extension and currently unsupported.
   .It Ic \&fspacewidth Ar font Op Ar afmunits
   Set a font-specific width for the space character.
   This is a Heirloom extension and currently ignored.
   .It Ic \&fspecial Ar curfont Op Ar font ...
   Conditionally define a special font.
   This is a groff extension and currently ignored.
   .It Ic \&ft Op Ar font
   Change the font.
   The following
   .Ar font
   arguments are supported:
   .Bl -tag -width 4n -offset indent
   .It Cm B , BI , 3 , 4
   switches to
   .Sy bold
   font
   .It Cm I , 2
   switches to
   .Em underlined
   font
   .It Cm R , CW , 1
   switches to normal font
   .It Cm P No "or no argument"
   switches back to the previous font
   .El
   .Pp
   This request takes effect only locally and may be overridden
   by macros and escape sequences.
   .It Ic \&ftr Ar newname Op Ar oldname
   Translate font name.
   This is a groff extension and currently ignored.
   .It Ic \&fzoom Ar font Op Ar permille
   Zoom font size.
   Currently ignored.
   .It Ic \&gcolor Op Ar colorname
   Set glyph color.
   This is a groff extension and currently ignored.
   .It Ic \&hc Op Ar char
   Set the hyphenation character.
   Currently ignored.
   .It Ic \&hcode Ar char code ...
   Set hyphenation codes of characters.
   Currently ignored.
   .It Ic \&hidechar Ar font char ...
   Hide characters in a font.
   This is a Heirloom extension and currently ignored.
   .It Ic \&hla Ar language
   Set hyphenation language.
   This is a groff extension and currently ignored.
   .It Ic \&hlm Op Ar number
   Set maximum number of consecutive hyphenated lines.
   Currently ignored.
   .It Ic \&hpf Ar filename
   Load hyphenation pattern file.
   This is a groff extension and currently ignored.
   .It Ic \&hpfa Ar filename
   Load hyphenation pattern file, appending to the current patterns.
   This is a groff extension and currently ignored.
   .It Ic \&hpfcode Ar code code ...
   Define mapping values for character codes in hyphenation patterns.
   This is a groff extension and currently ignored.
   .It Ic \&hw Ar word ...
   Specify hyphenation points in words.
   Currently ignored.
   .It Ic \&hy Op Ar mode
   Set automatic hyphenation mode.
   Currently ignored.
   .It Ic \&hylang Ar language
   Set hyphenation language.
   This is a Heirloom extension and currently ignored.
   .It Ic \&hylen Ar nchar
   Minimum word length for hyphenation.
   This is a Heirloom extension and currently ignored.
   .It Ic \&hym Op Ar length
   Set hyphenation margin.
   This is a groff extension and currently ignored.
   .It Ic \&hypp Ar penalty ...
   Define hyphenation penalties.
   This is a Heirloom extension and currently ignored.
   .It Ic \&hys Op Ar length
   Set hyphenation space.
   This is a groff extension and currently ignored.
   .It Ic \&ie Ar condition body
   The
   .Dq if
   half of an if/else conditional.
   The result of the conditional is pushed into a stack used by subsequent
   invocations of
   .Ic \&el ,
   which may be separated by any intervening input (or not exist at all).
   Its syntax is equivalent to
   .Ic \&if .
   .It Ic \&if Ar condition body
   Begin a conditional.
   This request can also be written as follows:
   .Bd -unfilled -offset indent
   .Pf . Ic \&if Ar condition No \e{ Ns Ar body
   .Ar body ... Ns \e}
   .Ed
   .Bd -unfilled -offset indent
   .Pf . Ic \&if Ar condition No \e{\e
   .Ar body ...
   .Pf . No \e}
   .Ed
   .Pp
   The
   .Ar condition
   is a boolean expression.
   Currently,
   .Xr mandoc 1
   supports the following subset of roff conditionals:
   .Bl -bullet
   .It
   If
   .Sq \&!
   is prefixed to
   .Ar condition ,
   it is logically inverted.
   .It
   If the first character of
   .Ar condition
   is
   .Sq n
   .Pq nroff mode
   or
   .Sq o
   .Pq odd page ,
   it evaluates to true.
   .It
   If the first character of
   .Ar condition
   is
   .Sq c
   .Pq character available ,
   .Sq e
   .Pq even page ,
   .Sq t
   .Pq troff mode ,
   or
   .Sq v
   .Pq vroff mode ,
   it evaluates to false.
   .It
   If the first character of
   .Ar condition
   is
   .Sq d ,
   it evaluates to true if the rest of
   .Ar condition
   is the name of an existing user defined macro or string;
   otherwise, it evaluates to false.
   .It
   If the first character of
   .Ar condition
   is
   .Sq r ,
   it evaluates to true if the rest of
   .Ar condition
   is the name of an existing number register;
   otherwise, it evaluates to false.
   .It
   If the
   .Ar condition
   starts with a parenthesis or with an optionally signed
   integer number, it is evaluated according to the rules of
   .Sx Numerical expressions
   explained below.
   It evaluates to true if the result is positive,
   or to false if the result is zero or negative.
   .It
   Otherwise, the first character of
   .Ar condition
   is regarded as a delimiter and it evaluates to true if the string
   extending from its first to its second occurrence is equal to the
   string extending from its second to its third occurrence.
   .It
   If
   .Ar condition
   cannot be parsed, it evaluates to false.
   .El
   .Pp
 If a conditional is false, its children are not processed, but are  If a conditional is false, its children are not processed, but are
 syntactically interpreted to preserve the integrity of the input  syntactically interpreted to preserve the integrity of the input
 document.  document.
 Thus,  Thus,
 .Pp  .Pp
 .D1 \&.if t \e .ig  .D1 \&.if t .ig
 .Pp  .Pp
 will discard the  will discard the
 .Sq \&.ig ,  .Sq \&.ig ,
 which may lead to interesting results, but  which may lead to interesting results, but
 .Pp  .Pp
 .D1 \&.if t \e .if t \e{\e  .D1 \&.if t .if t \e{\e
 .Pp  .Pp
 will continue to syntactically interpret to the block close of the final  will continue to syntactically interpret to the block close of the final
 conditional.  conditional.
 Sub-conditionals, in this case, obviously inherit the truth value of  Sub-conditionals, in this case, obviously inherit the truth value of
 the parent.  the parent.
 This macro has the following syntax:  
 .Pp  .Pp
 .Bd -literal -offset indent -compact  If the
 \&.if COND \e{\e  .Ar body
 BODY...  section is begun by an escaped brace
 \&.\e}  
 .Ed  
 .Bd -literal -offset indent -compact  
 \&.if COND \e{ BODY  
 BODY... \e}  
 .Ed  
 .Bd -literal -offset indent -compact  
 \&.if COND \e{ BODY  
 BODY...  
 \&.\e}  
 .Ed  
 .Bd -literal -offset indent -compact  
 \&.if COND \e  
 BODY  
 .Ed  
 .Pp  
 COND is a conditional (for the time being, this always evaluates to  
 false).  
 .Pp  
 If the BODY section is begun by an escaped brace  
 .Sq \e{ ,  .Sq \e{ ,
 scope continues until a closing-brace macro  scope continues until the end of the input line containing the
 .Sq \.\e} .  matching closing-brace escape sequence
 If the BODY is not enclosed in braces, scope continues until the next  .Sq \e} .
 macro or word.  If the
 If the COND is followed by a BODY on the same line, whether after a  .Ar body
 brace or not, then macros  is not enclosed in braces, scope continues until the end of the line.
   If the
   .Ar condition
   is followed by a
   .Ar body
   on the same line, whether after a brace or not, then requests and macros
 .Em must  .Em must
 begin with a control character.  begin with a control character.
 It is generally more intuitive, in this case, to write  It is generally more intuitive, in this case, to write
 .Bd -literal -offset indent  .Bd -unfilled -offset indent
 \&.if COND \e{\e  .Pf . Ic \&if Ar condition No \e{\e
 \&.foo  .Pf . Ar request
 bar  .Pf . No \e}
 \&.\e}  
 .Ed  .Ed
 .Pp  .Pp
 than having the macro follow as  than having the request or macro follow as
 .Pp  .Pp
 .D1 \&.if COND \e{ .foo  .D1 Pf . Ic \&if Ar condition Pf \e{. Ar request
 .Pp  .Pp
 The scope of a conditional is always parsed, but only executed if the  The scope of a conditional is always parsed, but only executed if the
 conditional evaluates to true.  conditional evaluates to true.
 .Pp  .Pp
 Note that text subsequent a  Note that the
 .Sq \&.\e}  
 macro is discarded.  
 Furthermore, if an explicit closing sequence  
 .Sq \e}  .Sq \e}
 is specified in a free-form line, the entire line is accepted within the  is converted into a zero-width escape sequence if not passed as a
 scope of the prior macro, not only the text preceding the close.  standalone macro
 .Ss \&ig  .Sq \&.\e} .
 Ignore input.  For example,
 Accepts the following syntax:  
 .Pp  .Pp
 .Bd -literal -offset indent -compact  .D1 \&.Fl a \e} b
 \&.ig  .Pp
 BODY...  will result in
   .Sq \e}
   being considered an argument of the
   .Sq \&Fl
   macro.
   .It Ic \&ig Op Ar endmacro
   Ignore input.
   Its syntax can be either
   .Bd -literal -offset indent
   .Pf . Cm \&ig
   .Ar ignored text
 \&..  \&..
 .Ed  .Ed
 .Bd -literal -offset indent -compact  .Pp
 \&.ig END  or
 BODY...  .Bd -literal -offset indent
 \&.END  .Pf . Cm \&ig Ar endmacro
   .Ar ignored text
   .Pf . Ar endmacro
 .Ed  .Ed
 .Pp  .Pp
 In the first case, input is ignored until a  In the first case, input is ignored until a
 .Sq \&..  .Sq \&..
 macro is encountered on its own line.  request is encountered on its own line.
 In the second case, input is ignored until a  In the second case, input is ignored until the specified
 .Sq \&.END  .Sq Pf . Ar endmacro
 is encountered.  is encountered.
 Text subsequent the  Do not use the escape character
 .Sq \&.END  
 or  
 .Sq \&..  
 is discarded.  
 .Pp  
 Do not use the escape  
 .Sq \e  .Sq \e
 anywhere in the definition of END.  anywhere in the definition of
 It causes very strange behaviour.  .Ar endmacro ;
 Furthermore, if you redefine a  it would cause very strange behaviour.
 .Nm  
 macro, such as  
 .Pp  .Pp
   When the
   .Ar endmacro
   is a roff request or a roff macro, like in
   .Pp
 .D1 \&.ig if  .D1 \&.ig if
 .Pp  .Pp
 the subsequent invocation of  the subsequent invocation of
 .Sx \&if  .Ic \&if
 will first signify the end of comment, then be invoked as a macro.  will first terminate the
 This behaviour really shouldn't be counted upon.  .Ar ignored text ,
   then be invoked as usual.
   Otherwise, it only terminates the
   .Ar ignored text ,
   and arguments following it or the
   .Sq \&..
   request are discarded.
   .It Ic \&in Op Oo Cm + Ns | Ns Cm - Oc Ns Ar width
   Change indentation.
   See
   .Xr man 7 .
   Ignored in
   .Xr mdoc 7 .
   .It Ic \&index Ar register stringname substring
   Find a substring in a string.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&it Ar expression macro
   Set an input line trap.
   The named
   .Ar macro
   will be invoked after processing the number of input text lines
   specified by the numerical
   .Ar expression .
   While evaluating the
   .Ar expression ,
   the unit suffixes described below
   .Sx Scaling Widths
   are ignored.
   .It Ic \&it Ar expression macro
   Set an input line trap, not counting lines ending with \ec.
   Currently unsupported.
   .It Ic \&IX Ar class keystring
   To support the generation of a table of contents,
   .Xr pod2man 1
   emits this user-defined macro, usually without defining it.
   To avoid reporting large numbers of spurious errors,
   .Xr mandoc 1
   ignores it.
   .It Ic \&kern Op Cm 1 | 0
   Switch kerning on or off.
   Currently ignored.
   .It Ic \&kernafter Ar font char ... afmunits ...
   Increase kerning after some characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&kernbefore Ar font char ... afmunits ...
   Increase kerning before some characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&kernpair Ar font char ... font char ... afmunits
   Add a kerning pair to the kerning table.
   This is a Heirloom extension and currently ignored.
   .It Ic \&lc Op Ar glyph
   Define a leader repetition character.
   Currently unsupported.
   .It Ic \&lc_ctype Ar localename
   Set the
   .Dv LC_CTYPE
   locale.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&lds Ar macroname string
   Define a local string.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&length Ar register string
   Count the number of input characters in a string.
   Currently unsupported.
   .It Ic \&letadj Ar lspmin lshmin letss lspmax lshmax
   Dynamic letter spacing and reshaping.
   This is a Heirloom extension and currently ignored.
   .It Ic \&lf Ar lineno Op Ar filename
   Change the line number for error messages.
   Ignored because insecure.
   .It Ic \&lg Op Cm 1 | 0
   Switch the ligature mechanism on or off.
   Currently ignored.
   .It Ic \&lhang Ar font char ... afmunits
   Hang characters at left margin.
   This is a Heirloom extension and currently ignored.
   .It Ic \&linetabs Op Cm 1 | 0
   Enable or disable line-tabs mode.
   This is a groff extension and currently unsupported.
   .It Ic \&ll Op Oo Cm + Ns | Ns Cm - Oc Ns Ar width
   Change the output line length.
   If the
   .Ar width
   argument is omitted, the line length is reset to its previous value.
   The default setting for terminal output is 78n.
   If a sign is given, the line length is added to or subtracted from;
   otherwise, it is set to the provided value.
   Using this request in new manuals is discouraged for several reasons,
   among others because it overrides the
   .Xr mandoc 1
   .Fl O Cm width
   command line option.
   .It Ic \&lnr Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar value Op Ar increment
   Set local number register.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&lnrf Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar value Op Ar increment
   Set local floating-point register.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&lpfx Ar string
   Set a line prefix.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&ls Op Ar factor
   Set line spacing.
   It takes one integer argument specifying the vertical distance of
   subsequent output text lines measured in v units.
   Currently ignored.
   .It Ic \&lsm Ar macroname
   Set a leading spaces trap.
   This is a groff extension and currently unsupported.
   .It Ic \&lt Op Oo Cm + Ns | Ns Cm - Oc Ns Ar width
   Set title line length.
   Currently ignored.
   .It Ic \&mc Ar glyph Op Ar dist
   Print margin character in the right margin.
   The
   .Ar dist
   is currently ignored; instead, 1n is used.
   .It Ic \&mediasize Ar media
   Set the device media size.
   This is a Heirloom extension and currently ignored.
   .It Ic \&minss Ar width
   Set minimum word space.
   This is a Heirloom extension and currently ignored.
   .It Ic \&mk Op Ar register
   Mark vertical position.
   Currently ignored.
   .It Ic \&mso Ar filename
   Load a macro file using the search path.
   Ignored because insecure.
   .It Ic \&na
   Disable adjusting without changing the adjustment mode.
   Currently ignored.
   .It Ic \&ne Op Ar height
   Declare the need for the specified minimum vertical space
   before the next trap or the bottom of the page.
   Currently ignored.
   .It Ic \&nf
   Switch to no-fill mode.
   See
   .Xr man 7 .
   Ignored by
   .Xr mdoc 7 .
   .It Ic \&nh
   Turn off automatic hyphenation mode.
   Currently ignored.
   .It Ic \&nhychar Ar char ...
   Define hyphenation-inhibiting characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&nm Op Ar start Op Ar inc Op Ar space Op Ar indent
   Print line numbers.
   Currently unsupported.
   .It Ic \&nn Op Ar number
   Temporarily turn off line numbering.
   Currently unsupported.
   .It Ic \&nop Ar body
   Execute the rest of the input line as a request or macro line.
   Currently unsupported.
   .It Ic \&nr Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar expression
   Define or change a register.
   A register is an arbitrary string value that defines some sort of state,
   which influences parsing and/or formatting.
   For the syntax of
   .Ar expression ,
   see
   .Sx Numerical expressions
   below.
   If it is prefixed by a sign, the register will be
   incremented or decremented instead of assigned to.
   .Pp
   The following
   .Ar register
   is handled specially:
   .Bl -tag -width Ds
   .It Cm nS
   If set to a positive integer value, certain
   .Xr mdoc 7
   macros will behave in the same way as in the
   .Em SYNOPSIS
   section.
   If set to 0, these macros will behave in the same way as outside the
   .Em SYNOPSIS
   section, even when called within the
   .Em SYNOPSIS
   section itself.
   Note that starting a new
   .Xr mdoc 7
   section with the
   .Ic \&Sh
   macro will reset this register.
   .El
   .It Xo
   .Ic \&nrf Ar register Oo Cm + Ns | Ns Cm - Oc Ns Ar expression
   .Op Ar increment
   .Xc
   Define or change a floating-point register.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&nroff
   Force nroff mode.
   This is a groff extension and currently ignored.
   .It Ic \&ns
   Turn on no-space mode.
   Currently ignored.
   .It Ic \&nx Op Ar filename
   Abort processing of the current input file and process another one.
   Ignored because insecure.
   .It Ic \&open Ar stream file
   Open a file for writing.
   Ignored because insecure.
   .It Ic \&opena Ar stream file
   Open a file for appending.
   Ignored because insecure.
   .It Ic \&os
   Output saved vertical space.
   Currently ignored.
   .It Ic \&output Ar string
   Output directly to intermediate output.
   Not supported.
   .It Ic \&padj Op Cm 1 | 0
   Globally control paragraph-at-once adjustment.
   This is a Heirloom extension and currently ignored.
   .It Ic \&papersize Ar media
   Set the paper size.
   This is a Heirloom extension and currently ignored.
   .It Ic \&pc Op Ar char
   Change the page number character.
   Currently ignored.
   .It Ic \&pev
   Print environments.
   This is a groff extension and currently ignored.
   .It Ic \&pi Ar command
   Pipe output to a shell command.
   Ignored because insecure.
   .It Ic \&PI
   Low-level request used by
   .Ic \&BP .
   This is a Heirloom extension and currently unsupported.
   .It Ic \&pl Op Oo Cm + Ns | Ns Cm - Oc Ns Ar height
   Change page length.
   Currently ignored.
   .It Ic \&pm
   Print names and sizes of macros, strings, and diversions
   to standard error output.
   Currently ignored.
   .It Ic \&pn Oo Cm + Ns | Ns Cm - Oc Ns Ar number
   Change the page number of the next page.
   Currently ignored.
   .It Ic \&pnr
   Print all number registers on standard error output.
   Currently ignored.
   .It Ic \&po Op Oo Cm + Ns | Ns Cm - Oc Ns Ar offset
   Set horizontal page offset.
   Currently ignored.
   .It Ic \&ps Op Oo Cm + Ns | Ns Cm - Oc Ns size
   Change point size.
   Currently ignored.
   .It Ic \&psbb Ar filename
   Retrieve the bounding box of a PostScript file.
   Currently unsupported.
   .It Ic \&pshape Ar indent length ...
   Set a special shape for the current paragraph.
   This is a Heirloom extension and currently unsupported.
   .It Ic \&pso Ar command
   Include output of a shell command.
   Ignored because insecure.
   .It Ic \&ptr
   Print the names and positions of all traps on standard error output.
   This is a groff extension and currently ignored.
   .It Ic \&pvs Op Oo Cm + Ns | Ns Cm - Oc Ns Ar height
   Change post-vertical spacing.
   This is a groff extension and currently ignored.
   .It Ic \&rchar Ar glyph ...
   Remove glyph definitions.
   Currently unsupported.
   .It Ic \&rd Op Ar prompt Op Ar agument ...
   Read from standard input.
   Currently ignored.
   .It Ic \&recursionlimit Ar maxrec maxtail
   Set the maximum stack depth for recursive macros.
   This is a Heirloom extension and currently ignored.
   .It Ic \&return Op Ar twice
   Exit a macro and return to the caller.
   Currently unsupported.
   .It Ic \&rfschar Ar font glyph ...
   Remove font-specific fallback glyph definitions.
   Currently unsupported.
   .It Ic \&rhang Ar font char ... afmunits
   Hang characters at right margin.
   This is a Heirloom extension and currently ignored.
   .It Ic \&rj Op Ar N
   Justify the next
   .Ar N
   input lines to the right margin without filling.
   .Ar N
   defaults to 1.
   An argument of 0 or less ends right adjustment.
   .It Ic \&rm Ar macroname
   Remove a request, macro or string.
   .It Ic \&rn Ar oldname newname
   Rename a request, macro, diversion, or string.
   In
   .Xr mandoc 1 ,
   user-defined macros,
   .Xr mdoc 7
   and
   .Xr man 7
   macros, and user-defined strings can be renamed, but renaming of
   predefined strings and of
   .Nm
   requests is not supported, and diversions are not implemented at all.
   .It Ic \&rnn Ar oldname newname
   Rename a number register.
   Currently unsupported.
   .It Ic \&rr Ar register
   Remove a register.
   .It Ic \&rs
   End no-space mode.
   Currently ignored.
   .It Ic \&rt Op Ar dist
   Return to marked vertical position.
   Currently ignored.
   .It Ic \&schar Ar glyph Op Ar string
   Define global fallback glyph.
   This is a groff extension and currently unsupported.
   .It Ic \&sentchar Ar char ...
   Define sentence-ending characters.
   This is a Heirloom extension and currently ignored.
   .It Ic \&shc Op Ar glyph
   Change the soft hyphen character.
   Currently ignored.
   .It Ic \&shift Op Ar number
   Shift macro arguments.
   Currently unsupported.
   .It Ic \&sizes Ar size ...
   Define permissible point sizes.
   This is a groff extension and currently ignored.
   .It Ic \&so Ar filename
   Include a source file.
   The file is read and its contents processed as input in place of the
   .Ic \&so
   request line.
   To avoid inadvertent inclusion of unrelated files,
   .Xr mandoc 1
   only accepts relative paths not containing the strings
   .Qq ../
   and
   .Qq /.. .
   .Pp
   This request requires
   .Xr man 1
   to change to the right directory before calling
   .Xr mandoc 1 ,
   per convention to the root of the manual tree.
   Typical usage looks like:
   .Pp
   .Dl \&.so man3/Xcursor.3
   .Pp
   As the whole concept is rather fragile, the use of
   .Ic \&so
   is discouraged.
   Use
   .Xr ln 1
   instead.
   .It Ic \&sp Op Ar height
   Break the output line and emit vertical space.
   The argument follows the syntax of
   .Sx Scaling Widths
   and defaults to one blank line
   .Pq Li 1v .
   .It Ic \&spacewidth Op Cm 1 | 0
   Set the space width from the font metrics file.
   This is a Heirloom extension and currently ignored.
   .It Ic \&special Op Ar font ...
   Define a special font.
   This is a groff extension and currently ignored.
   .It Ic \&spreadwarn Op Ar width
   Warn about wide spacing between words.
   Currently ignored.
   .It Ic \&ss Ar wordspace Op Ar sentencespace
   Set space character size.
   Currently ignored.
   .It Ic \&sty Ar position style
   Associate style with a font position.
   This is a groff extension and currently ignored.
   .It Ic \&substring Ar stringname startpos Op Ar endpos
   Replace a user-defined string with a substring.
   Currently unsupported.
   .It Ic \&sv Op Ar height
   Save vertical space.
   Currently ignored.
   .It Ic \&sy Ar command
   Execute shell command.
   Ignored because insecure.
   .It Ic \&T&
   Re-start a table layout, retaining the options of the prior table
   invocation.
   See
   .Sx \&TS .
   .It Ic \&ta Op Ar width ... Op Cm T Ar width ...
   Set tab stops.
   Each
   .Ar width
   argument follows the syntax of
   .Sx Scaling Widths .
   If prefixed by a plus sign, it is relative to the previous tab stop.
   The arguments after the
   .Cm T
   marker are used repeatedly as often as needed; for each reuse,
   they are taken relative to the last previously established tab stop.
   When
   .Ic \&ta
   is called without arguments, all tab stops are cleared.
   .It Ic \&tc Op Ar glyph
   Change tab repetition character.
   Currently unsupported.
   .It Ic \&TE
   End a table context.
   See
   .Sx \&TS .
   .It Ic \&ti Oo Cm + Ns | Ns Cm - Oc Ns Ar width
   Break the output line and indent the next output line by
   .Ar width .
   If a sign is specified, the temporary indentation is calculated
   relative to the current indentation; otherwise, it is absolute.
   The argument follows the syntax of
   .Sx Scaling Widths
   and the default scaling unit is
   .Cm m .
   .It Ic \&tkf Ar font minps width1 maxps width2
   Enable track kerning for a font.
   Currently ignored.
   .It Ic \&tl No \& Ap Ar left Ap Ar center Ap Ar right Ap
   Print a title line.
   Currently unsupported.
   .It Ic \&tm Ar string
   Print to standard error output.
   Currently ignored.
   .It Ic \&tm1 Ar string
   Print to standard error output, allowing leading blanks.
   This is a groff extension and currently ignored.
   .It Ic \&tmc Ar string
   Print to standard error output without a trailing newline.
   This is a groff extension and currently ignored.
   .It Ic \&tr Ar glyph glyph ...
   Output character translation.
   The first glyph in each pair is replaced by the second one.
   Character escapes can be used; for example,
   .Pp
   .Dl tr \e(xx\e(yy
   .Pp
   replaces all invocations of \e(xx with \e(yy.
   .It Ic \&track Ar font minps width1 maxps width2
   Static letter space tracking.
   This is a Heirloom extension and currently ignored.
   .It Ic \&transchar Ar char ...
   Define transparent characters for sentence-ending.
   This is a Heirloom extension and currently ignored.
   .It Ic \&trf Ar filename
   Output the contents of a file, disallowing invalid characters.
   This is a groff extension and ignored because insecure.
   .It Ic \&trimat Ar left top width height
   Set the TrimBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .It Ic \&trin Ar glyph glyph ...
   Output character translation, ignored by
   .Ic \&asciify .
   Currently unsupported.
   .It Ic \&trnt Ar glyph glyph ...
   Output character translation, ignored by \e!.
   Currently unsupported.
   .It Ic \&troff
   Force troff mode.
   This is a groff extension and currently ignored.
   .It Ic \&TS
   Begin a table, which formats input in aligned rows and columns.
   See
   .Xr tbl 7
   for a description of the tbl language.
   .It Ic \&uf Ar font
   Globally set the underline font.
   Currently ignored.
   .It Ic \&ul Op Ar N
   Underline next
   .Ar N
   input lines.
   Currently ignored.
   .It Ic \&unformat Ar divname
   Unformat spaces and tabs in a diversion.
   Currently unsupported.
   .It Ic \&unwatch Ar macroname
   Disable notification for string or macro.
   This is a Heirloom extension and currently ignored.
   .It Ic \&unwatchn Ar register
   Disable notification for register.
   This is a Heirloom extension and currently ignored.
   .It Ic \&vpt Op Cm 1 | 0
   Enable or disable vertical position traps.
   This is a groff extension and currently ignored.
   .It Ic \&vs Op Oo Cm + Ns | Ns Cm - Oc Ns Ar height
   Change vertical spacing.
   Currently ignored.
   .It Ic \&warn Ar flags
   Set warning level.
   Currently ignored.
   .It Ic \&warnscale Ar si
   Set the scaling indicator used in warnings.
   This is a groff extension and currently ignored.
   .It Ic \&watch Ar macroname
   Notify on change of string or macro.
   This is a Heirloom extension and currently ignored.
   .It Ic \&watchlength Ar maxlength
   On change, report the contents of macros and strings
   up to the specified length.
   This is a Heirloom extension and currently ignored.
   .It Ic \&watchn Ar register
   Notify on change of register.
   This is a Heirloom extension and currently ignored.
   .It Ic \&wh Ar dist Op Ar macroname
   Set a page location trap.
   Currently unsupported.
   .It Ic \&while Ar condition body
   Repeated execution while a condition is true.
   Currently unsupported.
   .It Ic \&write Oo \(dq Oc Ns Ar string
   Write to an open file.
   Ignored because insecure.
   .It Ic \&writec Oo \(dq Oc Ns Ar string
   Write to an open file without appending a newline.
   Ignored because insecure.
   .It Ic \&writem Ar macroname
   Write macro or string to an open file.
   Ignored because insecure.
   .It Ic \&xflag Ar level
   Set the extension level.
   This is a Heirloom extension and currently ignored.
   .El
   .Ss Numerical expressions
   The
   .Sx \&nr ,
   .Sx \&if ,
   and
   .Sx \&ie
   requests accept integer numerical expressions as arguments.
   These are always evaluated using the C
   .Vt int
   type; integer overflow works the same way as in the C language.
   Numbers consist of an arbitrary number of digits
   .Sq 0
   to
   .Sq 9
   prefixed by an optional sign
   .Sq +
   or
   .Sq - .
   Each number may be followed by one optional scaling unit described below
   .Sx Scaling Widths .
   The following equations hold:
   .Bd -literal -offset indent
   1i = 6v = 6P = 10m = 10n = 72p = 1000M = 240u = 240
   254c = 100i = 24000u = 24000
   1f = 65536u = 65536
   .Ed
   .Pp
   The following binary operators are implemented.
   Unless otherwise stated, they behave as in the C language:
   .Pp
   .Bl -tag -width 2n -compact
   .It Ic +
   addition
   .It Ic -
   subtraction
   .It Ic *
   multiplication
   .It Ic /
   division
   .It Ic %
   remainder of division
   .It Ic <
   less than
   .It Ic >
   greater than
   .It Ic ==
   equal to
   .It Ic =
   equal to, same effect as
   .Ic ==
   (this differs from C)
   .It Ic <=
   less than or equal to
   .It Ic >=
   greater than or equal to
   .It Ic <>
   not equal to (corresponds to C
   .Ic != ;
   this one is of limited portability, it is supported by Heirloom roff,
   but not by groff)
   .It Ic &
   logical and (corresponds to C
   .Ic && )
   .It Ic \&:
   logical or (corresponds to C
   .Ic || )
   .It Ic <?
   minimum (not available in C)
   .It Ic >?
   maximum (not available in C)
   .El
   .Pp
   There is no concept of precedence; evaluation proceeds from left to right,
   except when subexpressions are enclosed in parentheses.
   Inside parentheses, whitespace is ignored.
   .Sh ESCAPE SEQUENCE REFERENCE
   The
   .Xr mandoc 1
   .Nm
   parser recognises the following escape sequences.
   Note that the
   .Nm
   language defines more escape sequences not implemented in
   .Xr mandoc 1 .
   In
   .Xr mdoc 7
   and
   .Xr man 7
   documents, using escape sequences is discouraged except for those
   described in the
   .Sx LANGUAGE SYNTAX
   section above.
   .Pp
   A backslash followed by any character not listed here
   simply prints that character itself.
   .Ss \e<newline>
   A backslash at the end of an input line can be used to continue the
   logical input line on the next physical input line, joining the text
   on both lines together as if it were on a single input line.
   .Ss \e<space>
   The escape sequence backslash-space
   .Pq Sq \e\ \&
   is an unpaddable space-sized non-breaking space character; see
   .Sx Whitespace .
   .Ss \e\(dq
   The rest of the input line is treated as
   .Sx Comments .
   .Ss \e%
   Hyphenation allowed at this point of the word; ignored by
   .Xr mandoc 1 .
   .Ss \e&
   Non-printing zero-width character; see
   .Sx Whitespace .
   .Ss \e\(aq
   Acute accent special character; use
   .Sq \e(aa
   instead.
   .Ss \e( Ns Ar cc
   .Sx Special Characters
   with two-letter names, see
   .Xr mandoc_char 7 .
   .Ss \e*[ Ns Ar name ]
   Interpolate the string with the
   .Ar name ;
   see
   .Sx Predefined Strings
   and
   .Sx ds .
   For short names, there are variants
   .No \e* Ns Ar c
   and
   .No \e*( Ns Ar cc .
   .Ss \e,
   Left italic correction (groff extension); ignored by
   .Xr mandoc 1 .
   .Ss \e-
   Special character
   .Dq mathematical minus sign .
   .Ss \e/
   Right italic correction (groff extension); ignored by
   .Xr mandoc 1 .
   .Ss \e[ Ns Ar name ]
   .Sx Special Characters
   with names of arbitrary length, see
   .Xr mandoc_char 7 .
   .Ss \e^
   One-twelfth em half-narrow space character, effectively zero-width in
   .Xr mandoc 1 .
   .Ss \e`
   Grave accent special character; use
   .Sq \e(ga
   instead.
   .Ss \e{
   Begin conditional input; see
   .Sx if .
   .Ss \e\(ba
   One-sixth em narrow space character, effectively zero-width in
   .Xr mandoc 1 .
   .Ss \e}
   End conditional input; see
   .Sx if .
   .Ss \e~
   Paddable non-breaking space character.
   .Ss \e0
   Digit width space character.
   .Ss \eA\(aq Ns Ar string Ns \(aq
   Anchor definition; ignored by
   .Xr mandoc 1 .
   .Ss \eB\(aq Ns Ar string Ns \(aq
   Interpolate
   .Sq 1
   if
   .Ar string
   conforms to the syntax of
   .Sx Numerical expressions
   explained above and
   .Sq 0
   otherwise.
   .Ss \eb\(aq Ns Ar string Ns \(aq
   Bracket building function; ignored by
   .Xr mandoc 1 .
   .Ss \eC\(aq Ns Ar name Ns \(aq
   .Sx Special Characters
   with names of arbitrary length.
   .Ss \ec
   When encountered at the end of an input text line,
   the next input text line is considered to continue that line,
   even if there are request or macro lines in between.
   No whitespace is inserted.
   .Ss \eD\(aq Ns Ar string Ns \(aq
   Draw graphics function; ignored by
   .Xr mandoc 1 .
   .Ss \ed
   Move down by half a line; ignored by
   .Xr mandoc 1 .
   .Ss \ee
   Backslash special character.
   .Ss \eF[ Ns Ar name ]
   Switch font family (groff extension); ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .No \eF Ns Ar c
   and
   .No \eF( Ns Ar cc .
   .Ss \ef[ Ns Ar name ]
   Switch to the font
   .Ar name ,
   see
   .Sx Text Decoration .
   For short names, there are variants
   .No \ef Ns Ar c
   and
   .No \ef( Ns Ar cc .
   .Ss \eg[ Ns Ar name ]
   Interpolate the format of a number register; ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .No \eg Ns Ar c
   and
   .No \eg( Ns Ar cc .
   .Ss \eH\(aq Ns Oo +|- Oc Ns Ar number Ns \(aq
   Set the height of the current font; ignored by
   .Xr mandoc 1 .
   .Ss \eh\(aq Ns Ar width Ns \(aq
   Horizontal motion relative to the current position.
   The default scaling unit is
   .Cm m .
   .Ss \ek[ Ns Ar name ]
   Mark horizontal input place in register; ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .No \ek Ns Ar c
   and
   .No \ek( Ns Ar cc .
   .Ss \eL\(aq Ns Ar number Ns Oo Ar c Oc Ns \(aq
   Vertical line drawing function; ignored by
   .Xr mandoc 1 .
   .Ss \el\(aq Ns Ar width Ns Oo Ar c Oc Ns \(aq
   Draw a horizontal line of
   .Ar width
   using the glyph
   .Ar c .
   .Ss \eM[ Ns Ar name ]
   Set fill (background) color (groff extension); ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .No \eM Ns Ar c
   and
   .No \eM( Ns Ar cc .
   .Ss \em[ Ns Ar name ]
   Set glyph drawing color (groff extension); ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .No \em Ns Ar c
   and
   .No \em( Ns Ar cc .
   .Ss \eN\(aq Ns Ar number Ns \(aq
   Character
   .Ar number
   on the current font.
   .Ss \en[ Ns Ar name ]
   Interpolate the number register
   .Ar name .
   For short names, there are variants
   .No \en Ns Ar c
   and
   .No \en( Ns Ar cc .
   .Ss \eo\(aq Ns Ar string Ns \(aq
   Overstrike, writing all the characters contained in the
   .Ar string
   to the same output position.
   In terminal and HTML output modes,
   only the last one of the characters is visible.
   .Ss \ep
   Break the output line at the end of the current word.
   .Ss \eR\(aq Ns Ar name Oo +|- Oc Ns Ar number Ns \(aq
   Set number register; ignored by
   .Xr mandoc 1 .
   .Ss \eS\(aq Ns Ar number Ns \(aq
   Slant output; ignored by
   .Xr mandoc 1 .
   .Ss \es\(aq Ns Oo +|- Oc Ns Ar number Ns \(aq
   Change point size; ignored by
   .Xr mandoc 1 .
   Alternative forms
   .No \es Ns Oo +|- Oc Ns Ar n ,
   .No \es Ns Oo +|- Oc Ns \(aq Ns Ar number Ns \(aq ,
   .No \es Ns [ Oo +|- Oc Ns Ar number ] ,
   and
   .No \es Ns Oo +|- Oc Ns [ Ar number Ns ]
   are also parsed and ignored.
   .Ss \et
   Horizontal tab; ignored by
   .Xr mandoc 1 .
   .Ss \eu
   Move up by half a line; ignored by
   .Xr mandoc 1 .
   .Ss \eV[ Ns Ar name ]
   Interpolate an environment variable; ignored by
   .Xr mandoc 1 .
   For short names, there are variants
   .No \eV Ns Ar c
   and
   .No \eV( Ns Ar cc .
   .Ss \ev\(aq Ns Ar number Ns \(aq
   Vertical motion; ignored by
   .Xr mandoc 1 .
   .Ss \ew\(aq Ns Ar string Ns \(aq
   Interpolate the width of the
   .Ar string .
   The
   .Xr mandoc 1
   implementation assumes that after expansion of user-defined strings, the
   .Ar string
   only contains normal characters, no escape sequences, and that each
   character has a width of 24 basic units.
   .Ss \eX\(aq Ns Ar string Ns \(aq
   Output
   .Ar string
   as device control function; ignored in nroff mode and by
   .Xr mandoc 1 .
   .Ss \ex\(aq Ns Ar number Ns \(aq
   Extra line space function; ignored by
   .Xr mandoc 1 .
   .Ss \eY[ Ns Ar name ]
   Output a string as a device control function; ignored in nroff mode and by
   .Xr mandoc 1 .
   For short names, there are variants
   .No \eY Ns Ar c
   and
   .No \eY( Ns Ar cc .
   .Ss \eZ\(aq Ns Ar string Ns \(aq
   Print
   .Ar string
   with zero width and height; ignored by
   .Xr mandoc 1 .
   .Ss \ez
   Output the next character without advancing the cursor position.
 .Sh COMPATIBILITY  .Sh COMPATIBILITY
 This section documents compatibility between mandoc and other other  The
 troff implementations, at this time limited to GNU troff  .Xr mandoc 1
 .Pq Qq groff .  implementation of the
 The term  .Nm
 .Qq historic groff  language is intentionally incomplete.
 refers to groff versions before the  Unimplemented features include:
 .Pa doc.tmac  
 file re-write  
 .Pq somewhere between 1.15 and 1.19 .  
 .Pp  .Pp
 .Bl -dash -compact  .Bl -dash -compact
 .It  .It
 Historic groff did not accept white-space buffering the custom END tag  For security reasons,
 for the  .Xr mandoc 1
 .Sx \&ig  never reads or writes external files except via
 macro.  .Sx \&so
   requests with safe relative paths.
 .It  .It
   There is no automatic hyphenation, no adjustment to the right margin,
   and no centering; the output is always set flush-left.
   .It
   Support for setting tabulator positions
   and tabulator and leader characters is missing,
   and support for manually changing indentation is limited.
   .It
 The  The
 .Sx \&if  .Sq u
 and family would print funny white-spaces with historic groff when  scaling unit is the default terminal unit.
 depending on next-line syntax.  In traditional troff systems, this unit changes depending on the
   output media.
   .It
   Width measurements are implemented in a crude way
   and often yield wrong results.
   Explicit movement requests and escapes are ignored.
   .It
   There is no concept of output pages, no support for floats,
   graphics drawing, and picture inclusion;
   terminal output is always continuous.
   .It
   Requests regarding color, font families, and glyph manipulation
   are ignored.
   Font support is very limited.
   Kerning is not implemented, and no ligatures are produced.
   .It
   The
   .Qq \(aq
   macro control character does not suppress output line breaks.
   .It
   Diversions are not implemented,
   and support for traps is very incomplete.
   .It
   While recursion is supported,
   .Sx \&while
   loops are not.
 .El  .El
   .Pp
   The special semantics of the
   .Cm nS
   number register is an idiosyncracy of
   .Ox
   manuals and not supported by other
   .Xr mdoc 7
   implementations.
   .Sh SEE ALSO
   .Xr mandoc 1 ,
   .Xr eqn 7 ,
   .Xr man 7 ,
   .Xr mandoc_char 7 ,
   .Xr mdoc 7 ,
   .Xr tbl 7
   .Rs
   .%A Joseph F. Ossanna
   .%A Brian W. Kernighan
   .%I AT&T Bell Laboratories
   .%T Troff User's Manual
   .%R Computing Science Technical Report
   .%N 54
   .%C Murray Hill, New Jersey
   .%D 1976 and 1992
   .%U http://www.kohala.com/start/troff/cstr54.ps
   .Re
   .Rs
   .%A Joseph F. Ossanna
   .%A Brian W. Kernighan
   .%A Gunnar Ritter
   .%T Heirloom Documentation Tools Nroff/Troff User's Manual
   .%D September 17, 2007
   .%U http://heirloom.sourceforge.net/doctools/troff.pdf
   .Re
   .Sh HISTORY
   The RUNOFF typesetting system, whose input forms the basis for
   .Nm ,
   was written in MAD and FAP for the CTSS operating system by Jerome E.
   Saltzer in 1964.
   Doug McIlroy rewrote it in BCPL in 1969, renaming it
   .Nm .
   Dennis M. Ritchie rewrote McIlroy's
   .Nm
   in PDP-11 assembly for
   .At v1 ,
   Joseph F. Ossanna improved roff and renamed it nroff
   for
   .At v2 ,
   then ported nroff to C as troff, which Brian W. Kernighan released with
   .At v7 .
   In 1989, James Clarke re-implemented troff in C++, naming it groff.
 .Sh AUTHORS  .Sh AUTHORS
 The  .An -nosplit
   This
 .Nm  .Nm
 reference was written by  reference was written by
 .An Kristaps Dzonsons Aq kristaps@bsd.lv .  .An Kristaps Dzonsons Aq Mt kristaps@bsd.lv
   and
   .An Ingo Schwarze Aq Mt schwarze@openbsd.org .
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