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version 1.13, 2010/07/07 15:04:54 version 1.74, 2015/08/29 22:40:05
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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 Ingo Schwarze <schwarze@openbsd.org>  .\" Copyright (c) 2010, 2011, 2013-2015 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
 .Pp  
 An  
 .Nm  .Nm
 document follows simple rules:  lines beginning with the control  requests and escapes.
 characters  Only these requests and escapes supported by
 .Sq \.  .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
   Input lines beginning with the control character
   .Sq \&.
   are parsed for requests and macros.
   Such lines are called
   .Dq request lines
 or  or
 .Sq \(aq  .Dq macro lines ,
 are parsed for macros.  Other lines are interpreted within the scope of  respectively.
 prior macros:  Requests change the processing state and manipulate the formatting;
 .Bd -literal -offset indent  some macros also define the document structure and produce formatted
 \&.xx Macro lines change control state.  output.
 Other lines are interpreted within the current state.  The single quote
 .Ed  .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  .Sh LANGUAGE SYNTAX
 .Nm  .Nm
 documents may contain only graphable 7-bit ASCII characters, the space  documents may contain only graphable 7-bit ASCII characters, the space
 character, and, in certain circumstances, the tab character.  All  character, and, in certain circumstances, the tab character.
 manuals must have  The backslash character
 .Ux  .Sq \e
 line terminators.  indicates the start of an escape sequence, used for example for
 .Sh MACRO SYNTAX  .Sx Comments ,
 Macros are arbitrary in length and begin with a control character ,  .Sx Special Characters ,
 .Sq \.  .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 \(aq ,  .Sq v
 at the beginning of the line.  is necessarily non-portable across output media.
 An arbitrary amount of whitespace may sit between the control character  See
 and the macro name.  .Sx COMPATIBILITY .
 Thus, the following are equivalent:  .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
   at the beginning of the line,
   .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
 \&.if  \&.ig end
 \&.\ \ \ \&if  \&.ig    end
   \&.   ig end
 .Ed  .Ed
 .Sh REFERENCE  .Sh MACRO SYNTAX
 This section is a canonical reference of all macros, arranged  Macros are provided by the
 alphabetically.  .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.
   .Ss \&ab
   Abort processing.
   Currently unsupported.
   .Ss \&ad
   Set line adjustment mode.
   It takes one argument to select normal, left, right,
   or center adjustment for subsequent text.
   Currently ignored.
   .Ss \&af
   Assign an output format to a number register.
   Currently ignored.
   .Ss \&aln
   Create an alias for a number register.
   Currently unsupported.
   .Ss \&als
   Create an alias for a request, string, macro, or diversion.
   Currently unsupported.
 .Ss \&am  .Ss \&am
 The syntax of this macro is the same as that of  Append to a macro definition.
 .Sx \&ig ,  The syntax of this request is the same as that of
 except that a leading argument must be specified.  .Sx \&de .
 It is ignored, as are its children.  
 .Ss \&ami  
 The syntax of this macro is the same as that of  
 .Sx \&ig ,  
 except that a leading argument must be specified.  
 It is ignored, as are its children.  
 .Ss \&am1  .Ss \&am1
 The syntax of this macro is the same as that of  Append to a macro definition, switching roff compatibility mode off
 .Sx \&ig ,  during macro execution (groff extension).
 except that a leading argument must be specified.  The syntax of this request is the same as that of
 It is ignored, as are its children.  .Sx \&de1 .
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Sx \&am .
   .Ss \&ami
   Append to a macro definition, specifying the macro name indirectly
   (groff extension).
   The syntax of this request is the same as that of
   .Sx \&dei .
   .Ss \&ami1
   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
   .Sx \&dei1 .
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Sx \&ami .
   .Ss \&as
   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.
   .Ss \&as1
   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
   .Sx \&ds1 .
   Since
   .Xr mandoc 1
   does not implement
   .Nm
   compatibility mode at all, it handles this request as an alias for
   .Sx \&as .
   .Ss \&asciify
   Fully unformat a diversion.
   Currently unsupported.
   .Ss \&backtrace
   Print a backtrace of the input stack.
   This is a groff extension and currently ignored.
   .Ss \&bd
   Artificially embolden by repeated printing with small shifts.
   Currently ignored.
   .Ss \&bleedat
   Set the BleedBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .Ss \&blm
   Set a blank line trap.
   Currently unsupported.
   .Ss \&box
   Begin a diversion without including a partially filled line.
   Currently unsupported.
   .Ss \&boxa
   Add to a diversion without including a partially filled line.
   Currently unsupported.
   .Ss \&bp
   Begin new page.
   Currently ignored.
   .Ss \&BP
   Define a frame and place a picture in it.
   This is a Heirloom extension and currently unsupported.
   .Ss \&br
   Break the output line.
   See
   .Xr man 7
   and
   .Xr mdoc 7 .
   .Ss \&break
   Break out of a
   .Sx \&while
   loop.
   Currently unsupported.
   .Ss \&breakchar
   Optional line break characters.
   This is a Heirloom extension and currently ignored.
   .Ss \&brnl
   Break output line after next N input lines.
   This is a Heirloom extension and currently ignored.
   .Ss \&brp
   Break and spread output line.
   Currently, this is implemented as an alias for
   .Sx \&br .
   .Ss \&brpnl
   Break and spread output line after next N input lines.
   This is a Heirloom extension and currently ignored.
   .Ss \&c2
   Change the no-break control character.
   Currently unsupported.
   .Ss \&cc
   Change the control character.
   Its syntax is as follows:
   .Bd -literal -offset indent
   .Pf . Cm \&cc Op Ar c
   .Ed
   .Pp
   If
   .Ar c
   is not specified, the control character is reset to
   .Sq \&. .
   Trailing characters are ignored.
   .Ss \&ce
   Center some lines.
   It takes one integer argument, specifying how many lines to center.
   Currently ignored.
   .Ss \&cf
   Output the contents of a file.
   Ignored because insecure.
   .Ss \&cflags
   Set character flags.
   This is a groff extension and currently ignored.
   .Ss \&ch
   Change a trap location.
   Currently ignored.
   .Ss \&char
   Define a new glyph.
   Currently unsupported.
   .Ss \&chop
   Remove the last character from a macro, string, or diversion.
   Currently unsupported.
   .Ss \&class
   Define a character class.
   This is a groff extension and currently ignored.
   .Ss \&close
   Close an open file.
   Ignored because insecure.
   .Ss \&CL
   Print text in color.
   This is a Heirloom extension and currently unsupported.
   .Ss \&color
   Activate or deactivate colors.
   This is a groff extension and currently ignored.
   .Ss \&composite
   Define a name component for composite glyph names.
   This is a groff extension and currently unsupported.
   .Ss \&continue
   Immediately start the next iteration of a
   .Sx \&while
   loop.
   Currently unsupported.
   .Ss \&cp
   Switch
   .Nm
   compatibility mode on or off.
   Currently ignored.
   .Ss \&cropat
   Set the CropBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .Ss \&cs
   Constant character spacing mode.
   Currently ignored.
   .Ss \&cu
   Underline including whitespace.
   Currently ignored.
   .Ss \&da
   Append to a diversion.
   Currently unsupported.
   .Ss \&dch
   Change a trap location in the current diversion.
   This is a Heirloom extension and currently unsupported.
 .Ss \&de  .Ss \&de
 The syntax of this macro is the same as that of  Define a
 .Sx \&ig ,  .Nm
 except that a leading argument must be specified.  macro.
 It is ignored, as are its children.  Its syntax can be either
   .Bd -literal -offset indent
   .Pf . Cm \&de Ar name
   .Ar macro definition
   \&..
   .Ed
   .Pp
   or
   .Bd -literal -offset indent
   .Pf . Cm \&de Ar name Ar end
   .Ar macro definition
   .Pf . Ar end
   .Ed
   .Pp
   Both forms define or redefine the macro
   .Ar name
   to represent the
   .Ar macro definition ,
   which may consist of one or more input lines, including the newline
   characters terminating each line, optionally containing calls to
   .Nm
   requests,
   .Nm
   macros or high-level macros like
   .Xr man 7
   or
   .Xr mdoc 7
   macros, whichever applies to the document in question.
   .Pp
   Specifying a custom
   .Ar end
   macro works in the same way as for
   .Sx \&ig ;
   namely, the call to
   .Sq Pf . Ar end
   first ends the
   .Ar macro definition ,
   and after that, it is also evaluated as a
   .Nm
   request or
   .Nm
   macro, but not as a high-level macro.
   .Pp
   The macro can be invoked later using the syntax
   .Pp
   .D1 Pf . Ar name Op Ar argument Op Ar argument ...
   .Pp
   Regarding argument parsing, see
   .Sx MACRO SYNTAX
   above.
   .Pp
   The line invoking the macro will be replaced
   in the input stream by the
   .Ar macro 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 name
   clobbers the user-defined string
   .Ar name ,
   and the
   .Ar macro definition
   can also be printed using the
   .Sq \e*
   string interpolation syntax described below
   .Sx 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.
   .Ss \&de1
   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
   .Sx \&de .
   .Ss \&defcolor
   Define a color name.
   This is a groff extension and currently ignored.
 .Ss \&dei  .Ss \&dei
 The syntax of this macro is the same as that of  Define a
 .Sx \&ig ,  .Nm
 except that a leading argument must be specified.  macro, specifying the macro name indirectly (groff extension).
 It is ignored, as are its children.  The syntax of this request is the same as that of
   .Sx \&de .
   The request
   .Pp
   .D1 Pf . Cm \&dei Ar name Op Ar end
   .Pp
   has the same effect as:
   .Pp
   .D1 Pf . Cm \&de No \e* Ns Bo Ar name Bc Op \e* Ns Bq Ar end
   .Ss \&dei1
   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
   .Sx \&dei .
   .Ss \&device
   This request only makes sense with the groff-specific intermediate
   output format and is unsupported.
   .Ss \&devicem
   This request only makes sense with the groff-specific intermediate
   output format and is unsupported.
   .Ss \&di
   Begin a diversion.
   Currently unsupported.
   .Ss \&do
   Execute
   .Nm
   request or macro line with compatibility mode disabled.
   Currently unsupported.
 .Ss \&ds  .Ss \&ds
 Define a reserved word.  Define a user-defined string.
 Its syntax is as follows:  Its syntax is as follows:
 .Pp  .Pp
 .D1 Pf \. Sx \&ds No Cm key val  .D1 Pf . Cm \&ds Ar name Oo \(dq Oc Ns Ar string
 .Pp  .Pp
 The  The
 .Cm key  .Ar name
 and  and
 .Cm val  .Ar string
 strings are space-separated.  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  The
 .Cm key  .Ar string
 values may be invoked in subsequent text by using \e*(NN for two-letter  can be interpolated into subsequent text by using
 pairs, \e*N for one-letter, and \e*[NNN] for arbitrary-length values.  .No \e* Ns Bq Ar name
 .Ss \&de1  for a
 The syntax of this macro is the same as that of  .Ar name
 .Sx \&ig ,  of arbitrary length, or \e*(NN or \e*N if the length of
 except that a leading argument must be specified.  .Ar name
 It is ignored, as are its children.  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 name
   clobbers the macro
   .Ar name ,
   and the
   .Ar name
   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
   .Cm SH
   macro when used in a
   .Xr man 7
   document.
   Such abuse is of course strongly discouraged.
   .Ss \&ds1
   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
   .Sx \&ds .
   .Ss \&dwh
   Set a location trap in the current diversion.
   This is a Heirloom extension and currently unsupported.
   .Ss \&dt
   Set a trap within a diversion.
   Currently unsupported.
   .Ss \&ec
   Change the escape character.
   Currently unsupported.
   .Ss \&ecs
   Restore the escape character.
   Currently unsupported.
   .Ss \&ecr
   Save the escape character.
   Currently unsupported.
 .Ss \&el  .Ss \&el
 The  The
 .Qq else  .Qq else
Line 122  If no stack entries are present (e.g., due to no prior
Line 840  If no stack entries are present (e.g., due to no prior
 .Sx \&ie  .Sx \&ie
 calls)  calls)
 then false is assumed.  then false is assumed.
 The syntax of this macro is similar to  The syntax of this request is similar to
 .Sx \&if  .Sx \&if
 except that the conditional is missing.  except that the conditional is missing.
   .Ss \&em
   Set a trap at the end of input.
   Currently unsupported.
   .Ss \&EN
   End an equation block.
   See
   .Sx \&EQ .
   .Ss \&eo
   Disable the escape mechanism completely.
   Currently unsupported.
   .Ss \&EP
   End a picture started by
   .Sx \&BP .
   This is a Heirloom extension and currently unsupported.
   .Ss \&EQ
   Begin an equation block.
   See
   .Xr eqn 7
   for a description of the equation language.
   .Ss \&errprint
   Print a string like an error message.
   This is a Heirloom extension and currently ignored.
   .Ss \&ev
   Switch to another environment.
   Currently unsupported.
   .Ss \&evc
   Copy an environment into the current environment.
   Currently unsupported.
   .Ss \&ex
   Abort processing and exit.
   Currently unsupported.
   .Ss \&fallback
   Select the fallback sequence for a font.
   This is a Heirloom extension and currently ignored.
   .Ss \&fam
   Change the font family.
   Takes one argument specifying the font family to be selected.
   It is a groff extension and currently ignored.
   .Ss \&fc
   Define a delimiting and a padding character for fields.
   Currently unsupported.
   .Ss \&fchar
   Define a fallback glyph.
   Currently unsupported.
   .Ss \&fcolor
   Set the fill color for \eD objects.
   This is a groff extension and currently ignored.
   .Ss \&fdeferlig
   Defer ligature building.
   This is a Heirloom extension and currently ignored.
   .Ss \&feature
   Enable or disable an OpenType feature.
   This is a Heirloom extension and currently ignored.
   .Ss \&fi
   Switch to fill mode.
   See
   .Xr man 7 .
   Ignored in
   .Xr mdoc 7 .
   .Ss \&fkern
   Control the use of kerning tables for a font.
   This is a Heirloom extension and currently ignored.
   .Ss \&fl
   Flush output.
   Currently ignored.
   .Ss \&flig
   Define ligatures.
   This is a Heirloom extension and currently ignored.
   .Ss \&fp
   Assign font position.
   Currently ignored.
   .Ss \&fps
   Mount a font with a special character map.
   This is a Heirloom extension and currently ignored.
   .Ss \&fschar
   Define a font-specific fallback glyph.
   This is a groff extension and currently unsupported.
   .Ss \&fspacewidth
   Set a font-specific width for the space character.
   This is a Heirloom extension and currently ignored.
   .Ss \&fspecial
   Conditionally define a special font.
   This is a groff extension and currently ignored.
   .Ss \&ft
   Change the font.
   Its syntax is as follows:
   .Pp
   .D1 Pf . Cm \&ft Op Ar font
   .Pp
   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, may be overridden by macros
   and escape sequences, and is only supported in
   .Xr man 7
   for now.
   .Ss \&ftr
   Translate font name.
   This is a groff extension and currently ignored.
   .Ss \&fzoom
   Zoom font size.
   Currently ignored.
   .Ss \&gcolor
   Set glyph color.
   This is a groff extension and currently ignored.
   .Ss \&hc
   Set the hyphenation character.
   Currently ignored.
   .Ss \&hcode
   Set hyphenation codes of characters.
   Currently ignored.
   .Ss \&hidechar
   Hide characters in a font.
   This is a Heirloom extension and currently ignored.
   .Ss \&hla
   Set hyphenation language.
   This is a groff extension and currently ignored.
   .Ss \&hlm
   Set maximum number of consecutive hyphenated lines.
   Currently ignored.
   .Ss \&hpf
   Load hyphenation pattern file.
   This is a groff extension and currently ignored.
   .Ss \&hpfa
   Load hyphenation pattern file, appending to the current patterns.
   This is a groff extension and currently ignored.
   .Ss \&hpfcode
   Define mapping values for character codes in hyphenation patterns.
   This is a groff extension and currently ignored.
   .Ss \&hw
   Specify hyphenation points in words.
   Currently ignored.
   .Ss \&hy
   Set automatic hyphenation mode.
   Currently ignored.
   .Ss \&hylang
   Set hyphenation language.
   This is a Heirloom extension and currently ignored.
   .Ss \&hylen
   Minimum word length for hyphenation.
   This is a Heirloom extension and currently ignored.
   .Ss \&hym
   Set hyphenation margin.
   This is a groff extension and currently ignored.
   .Ss \&hypp
   Define hyphenation penalties.
   This is a Heirloom extension and currently ignored.
   .Ss \&hys
   Set hyphenation space.
   This is a groff extension and currently ignored.
 .Ss \&ie  .Ss \&ie
 The  The
 .Qq if  .Qq if
Line 137  Its syntax is equivalent to
Line 1020  Its syntax is equivalent to
 .Sx \&if .  .Sx \&if .
 .Ss \&if  .Ss \&if
 Begins a conditional.  Begins a conditional.
 Right now, the conditional evaluates to true  This request has the following syntax:
 if and only if it starts with the letter  .Bd -literal -offset indent
 .Sy n ,  \&.if COND BODY
 indicating processing in  .Ed
 .Xr nroff 1  .Bd -literal -offset indent
 style as opposed to  \&.if COND \e{BODY
 .Xr troff 1  BODY...\e}
 style.  .Ed
   .Bd -literal -offset indent
   \&.if COND \e{\e
   BODY...
   \&.\e}
   .Ed
   .Pp
   COND is a conditional statement.
   Currently,
   .Xr mandoc 1
   supports the following subset of roff conditionals:
   .Bl -bullet
   .It
   If
   .Sq \&!
   is prefixed to COND, the condition is logically inverted.
   .It
   If the first character of COND is
   .Sq n
   .Pq nroff mode
   or
   .Sq o
   .Pq odd page ,
   COND evaluates to true.
   .It
   If the first character of COND is
   .Sq c
   .Pq character available ,
   .Sq d
   .Pq string defined ,
   .Sq e
   .Pq even page ,
   .Sq t
   .Pq troff mode ,
   or
   .Sq v
   .Pq vroff mode ,
   COND evaluates to false.
   .It
   If the first character of COND is
   .Sq r ,
   it evalutes to true if the rest of COND is the name of an existing
   number register; otherwise, it evaluates to false.
   .It
   If COND 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 COND is regarded as a delimiter
   and COND 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 COND 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 COND \e{\e  
 BODY...  
 \&.\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 statement.  
 roff allows for complicated conditionals; mandoc is much simpler.  
 At this time, mandoc supports only  
 .Sq n ,  
 evaluating to true;  
 and  
 .Sq t ,  
 .Sq e ,  
 and  
 .Sq o ,  
 evaluating to false.  
 All other invocations are read up to the next end of line or space and  
 evaluate as false.  
 .Pp  
 If the BODY section is begun by an escaped brace  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 BODY is not enclosed in braces, scope continues until
   the end of the line.
 If the COND is followed by a BODY on the same line, whether after a  If the COND is followed by a BODY on the same line, whether after a
 brace or not, then macros  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
Line 215  bar
Line 1123  bar
 \&.\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 \&.if COND \e{ .foo
 .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, with the  standalone macro
   .Sq \&.\e} .
   For example,
   .Pp
   .D1 \&.Fl a \e} b
   .Pp
   will result in
 .Sq \e}  .Sq \e}
 collapsing into a zero-width space.  being considered an argument of the
   .Sq \&Fl
   macro.
 .Ss \&ig  .Ss \&ig
 Ignore input.  Ignore input.
 Accepts the following syntax:  Its syntax can be either
 .Pp  .Bd -literal -offset indent
 .Bd -literal -offset indent -compact  .Pf . Cm \&ig
 \&.ig  .Ar ignored text
 BODY...  
 \&..  \&..
 .Ed  .Ed
 .Bd -literal -offset indent -compact  .Pp
 \&.ig END  or
 BODY...  .Bd -literal -offset indent
 \&.END  .Pf . Cm \&ig Ar end
   .Ar ignored text
   .Pf . Ar end
 .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 end
 is encountered.  macro 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 end ;
 Furthermore, if you redefine a  it would cause very strange behaviour.
 .Nm  
 macro, such as  
 .Pp  .Pp
   When the
   .Ar end
   macro 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  .Sx \&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 ,
 .Ss \&rm  then be invoked as usual.
 Remove a request, macro or string.  Otherwise, it only terminates the
 This macro is intended to have one argument,  .Ar ignored text ,
 the name of the request, macro or string to be undefined.  and arguments following it or the
 Currently, it is ignored including its arguments,  .Sq \&..
 and the number of arguments is not checked.  request are discarded.
   .Ss \&in
   Change indentation.
   See
   .Xr man 7 .
   Ignored in
   .Xr mdoc 7 .
   .Ss \&index
   Find a substring in a string.
   This is a Heirloom extension and currently unsupported.
   .Ss \&it
   Set an input line trap.
   Its syntax is as follows:
   .Pp
   .D1 Pf . Cm it Ar expression macro
   .Pp
   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.
   .Ss \&itc
   Set an input line trap, not counting lines ending with \ec.
   Currently unsupported.
   .Ss \&IX
   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.
   .Ss \&kern
   Switch kerning on or off.
   Currently ignored.
   .Ss \&kernafter
   Increase kerning after some characters.
   This is a Heirloom extension and currently ignored.
   .Ss \&kernbefore
   Increase kerning before some characters.
   This is a Heirloom extension and currently ignored.
   .Ss \&kernpair
   Add a kerning pair to the kerning table.
   This is a Heirloom extension and currently ignored.
   .Ss \&lc
   Define a leader repetition character.
   Currently unsupported.
   .Ss \&lc_ctype
   Set the
   .Dv LC_CTYPE
   locale.
   This is a Heirloom extension and currently unsupported.
   .Ss \&lds
   Define a local string.
   This is a Heirloom extension and currently unsupported.
   .Ss \&length
   Count the number of input characters in a user-defined string.
   Currently unsupported.
   .Ss \&letadj
   Dynamic letter spacing and reshaping.
   This is a Heirloom extension and currently ignored.
   .Ss \&lf
   Change the line number for error messages.
   Ignored because insecure.
   .Ss \&lg
   Switch the ligature mechanism on or off.
   Currently ignored.
   .Ss \&lhang
   Hang characters at left margin.
   This is a Heirloom extension and currently ignored.
   .Ss \&linetabs
   Enable or disable line-tabs mode.
   This is a groff extension and currently unsupported.
   .Ss \&ll
   Change the output line length.
   Its syntax is as follows:
   .Pp
   .D1 Pf . Cm \&ll Op Oo +|- Oc Ns Ar width
   .Pp
   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.
   .Ss \&lnr
   Set local number register.
   This is a Heirloom extension and currently unsupported.
   .Ss \&lnrf
   Set local floating-point register.
   This is a Heirloom extension and currently unsupported.
   .Ss \&lpfx
   Set a line prefix.
   This is a Heirloom extension and currently unsupported.
   .Ss \&ls
   Set line spacing.
   It takes one integer argument specifying the vertical distance of
   subsequent output text lines measured in v units.
   Currently ignored.
   .Ss \&lsm
   Set a leading spaces trap.
   This is a groff extension and currently unsupported.
   .Ss \&lt
   Set title line length.
   Currently ignored.
   .Ss \&mc
   Print margin character in the right margin.
   Currently ignored.
   .Ss \&mediasize
   Set the device media size.
   This is a Heirloom extension and currently ignored.
   .Ss \&minss
   Set minimum word space.
   This is a Heirloom extension and currently ignored.
   .Ss \&mk
   Mark vertical position.
   Currently ignored.
   .Ss \&mso
   Load a macro file.
   Ignored because insecure.
   .Ss \&na
   Disable adjusting without changing the adjustment mode.
   Currently ignored.
   .Ss \&ne
   Declare the need for the specified minimum vertical space
   before the next trap or the bottom of the page.
   Currently ignored.
   .Ss \&nf
   Switch to no-fill mode.
   See
   .Xr man 7 .
   Ignored by
   .Xr mdoc 7 .
   .Ss \&nh
   Turn off automatic hyphenation mode.
   Currently ignored.
   .Ss \&nhychar
   Define hyphenation-inhibiting characters.
   This is a Heirloom extension and currently ignored.
   .Ss \&nm
   Print line numbers.
   Currently unsupported.
   .Ss \&nn
   Temporarily turn off line numbering.
   Currently unsupported.
   .Ss \&nop
   Exexute the rest of the input line as a request or macro line.
   Currently unsupported.
 .Ss \&nr  .Ss \&nr
 Define a register.  Define or change a register.
 A register is an arbitrary string value that defines some sort of state,  A register is an arbitrary string value that defines some sort of state,
 which influences parsing and/or formatting.  which influences parsing and/or formatting.
 Its syntax is as follows:  Its syntax is as follows:
 .Pp  .Pp
 .D1 Pf \. Sx \&nr Cm name value  .D1 Pf \. Cm \&nr Ar name Oo +|- Oc Ns Ar expression
 .Pp  .Pp
 The  For the syntax of
 .Cm value  .Ar expression ,
 may, at the moment, only be an integer.  see
 The  .Sx Numerical expressions
 .Cm name  below.
 is defined up to the next whitespace.  If it is prefixed by a sign, the register will be
   incremented or decremented instead of assigned to.
   .Pp
 The following register  The following register
 .Cm name  .Ar name
 requests are recognised:  is handled specially:
 .Bl -tag -width Ds  .Bl -tag -width Ds
 .It Cm nS  .It Cm nS
 If set to a positive integer value, certain  If set to a positive integer value, certain
 .Xr mdoc 7  .Xr mdoc 7
 macros will behave as if they were defined in the  macros will behave in the same way as in the
 .Em SYNOPSIS  .Em SYNOPSIS
 section.  section.
 Otherwise, this behaviour is unset (even if called within the  If set to 0, these macros will behave in the same way as outside the
 .Em SYNOPSIS  .Em SYNOPSIS
 section itself).  section, even when called within the
 Note that invoking a new  .Em SYNOPSIS
   section itself.
   Note that starting a new
 .Xr mdoc 7  .Xr mdoc 7
 section will unset this value.  section with the
   .Cm \&Sh
   macro will reset this register.
 .El  .El
   .Ss \&nrf
   Define or change a floating-point register.
   This is a Heirloom extension and currently unsupported.
   .Ss \&nroff
   Force nroff mode.
   This is a groff extension and currently ignored.
   .Ss \&ns
   Turn on no-space mode.
   Currently ignored.
   .Ss \&nx
   Abort processing of the current input file and process another one.
   Ignored because insecure.
   .Ss \&open
   Open a file for writing.
   Ignored because insecure.
   .Ss \&opena
   Open a file for appending.
   Ignored because insecure.
   .Ss \&os
   Output saved vertical space.
   Currently ignored.
   .Ss \&output
   Output directly to intermediate output.
   Not supported.
   .Ss \&padj
   Globally control paragraph-at-once adjustment.
   This is a Heirloom extension and currently ignored.
   .Ss \&papersize
   Set the paper size.
   This is a Heirloom extension and currently ignored.
   .Ss \&pc
   Change the page number character.
   Currently ignored.
   .Ss \&pev
   Print environments.
   This is a groff extension and currently ignored.
   .Ss \&pi
   Pipe output to a shell command.
   Ignored because insecure.
   .Ss \&PI
   Low-level request used by
   .Sx \&BP .
   This is a Heirloom extension and currently unsupported.
   .Ss \&pl
   Change page length.
   Takes one height argument.
   Currently ignored.
   .Ss \&pm
   Print names and sizes of macros, strings, and diversions.
   Currently ignored.
   .Ss \&pn
   Change page number of the next page.
   Currently ignored.
   .Ss \&pnr
   Print all number registers.
   Currently ignored.
   .Ss \&po
   Set horizontal page offset.
   Currently ignored.
   .Ss \&ps
   Change point size.
   Takes one numerical argument.
   Currently ignored.
   .Ss \&psbb
   Retrieve the bounding box of a PostScript file.
   Currently unsupported.
   .Ss \&pshape
   Set a special shape for the current paragraph.
   This is a Heirloom extension and currently unsupported.
   .Ss \&pso
   Include output of a shell command.
   Ignored because insecure.
   .Ss \&ptr
   Print the names and positions of all traps.
   This is a groff extension and currently ignored.
   .Ss \&pvs
   Change post-vertical spacing.
   This is a groff extension and currently ignored.
   .Ss \&rchar
   Remove glyph definitions.
   Currently unsupported.
   .Ss \&rd
   Read from standard input.
   Currently ignored.
   .Ss \&recursionlimit
   Set the maximum stack depth for recursive macros.
   This is a Heirloom extension and currently ignored.
   .Ss \&return
   Exit a macro and return to the caller.
   Currently unsupported.
   .Ss \&rfschar
   Remove font-specific fallback glyph definitions.
   Currently unsupported.
   .Ss \&rhang
   Hang characters at right margin.
   This is a Heirloom extension and currently ignored.
   .Ss \&rj
   Justify unfilled text to the right margin.
   Currently ignored.
   .Ss \&rm
   Remove a request, macro or string.
   Its syntax is as follows:
   .Pp
   .D1 Pf \. Cm \&rm Ar name
   .Ss \&rn
   Rename a request, macro, diversion, or string.
   Currently unsupported.
   .Ss \&rnn
   Rename a number register.
   Currently unsupported.
   .Ss \&rr
   Remove a register.
   Its syntax is as follows:
   .Pp
   .D1 Pf \. Cm \&rr Ar name
   .Ss \&rs
   End no-space mode.
   Currently ignored.
   .Ss \&rt
   Return to marked vertical position.
   Currently ignored.
   .Ss \&schar
   Define global fallback glyph.
   This is a groff extension and currently unsupported.
   .Ss \&sentchar
   Define sentence-ending characters.
   This is a Heirloom extension and currently ignored.
   .Ss \&shc
   Change the soft hyphen character.
   Currently ignored.
   .Ss \&shift
   Shift macro arguments.
   Currently unsupported.
   .Ss \&sizes
   Define permissible point sizes.
   This is a groff extension and currently ignored.
   .Ss \&so
   Include a source file.
   Its syntax is as follows:
   .Pp
   .D1 Pf \. Cm \&so Ar file
   .Pp
   The
   .Ar file
   will be read and its contents processed as input in place of the
   .Sq \&.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
   .Sx \&so
   is discouraged.
   Use
   .Xr ln 1
   instead.
   .Ss \&spacewidth
   Set the space width from the font metrics file.
   This is a Heirloom extension and currently ignored.
   .Ss \&special
   Define a special font.
   This is a groff extension and currently ignored.
   .Ss \&spreadwarn
   Warn about wide spacing between words.
   Currently ignored.
   .Ss \&ss
   Set space character size.
   Currently ignored.
   .Ss \&sty
   Associate style with a font position.
   This is a groff extension and currently ignored.
   .Ss \&substring
   Replace a user-defined string with a substring.
   Currently unsupported.
   .Ss \&sv
   Save vertical space.
   Currently ignored.
   .Ss \&sy
   Execute shell command.
   Ignored because insecure.
   .Ss \&T&
   Re-start a table layout, retaining the options of the prior table
   invocation.
   See
   .Sx \&TS .
   .Ss \&ta
   Set tab stops.
   Takes an arbitrary number of arguments.
   Currently unsupported.
   .Ss \&tc
   Change tab repetion character.
   Currently unsupported.
   .Ss \&TE
   End a table context.
   See
   .Sx \&TS .
   .Ss \&ti
   Temporary indent.
   Currently unsupported.
   .Ss \&tkf
   Enable track kerning for a font.
   Currently ignored.
   .Ss \&tl
   Print a title line.
   Currently unsupported.
   .Ss \&tm
   Print to standard error output.
   Currently ignored.
   .Ss \&tm1
   Print to standard error output, allowing leading blanks.
   This is a groff extension and currently ignored.
   .Ss \&tmc
   Print to standard error output without a trailing newline.
   This is a groff extension and currently ignored.
 .Ss \&tr  .Ss \&tr
 Output character translation.  Output character translation.
 This macro is intended to have one argument,  Its syntax is as follows:
 consisting of an even number of characters.  .Pp
 Currently, it is ignored including its arguments,  .D1 Pf \. Cm \&tr Ar [ab]+
 and the number of arguments is not checked.  .Pp
   Pairs of
   .Ar ab
   characters are replaced
   .Ar ( a
   for
   .Ar b ) .
   Replacement (or origin) characters may also be character escapes; thus,
   .Pp
   .Dl tr \e(xx\e(yy
   .Pp
   replaces all invocations of \e(xx with \e(yy.
   .Ss \&track
   Static letter space tracking.
   This is a Heirloom extension and currently ignored.
   .Ss \&transchar
   Define transparent characters for sentence-ending.
   This is a Heirloom extension and currently ignored.
   .Ss \&trf
   Output the contents of a file, disallowing invalid characters.
   This is a groff extension and ignored because insecure.
   .Ss \&trimat
   Set the TrimBox page parameter for PDF generation.
   This is a Heirloom extension and currently ignored.
   .Ss \&trin
   Output character translation, ignored by
   .Cm \&asciify .
   Currently unsupported.
   .Ss \&trnt
   Output character translation, ignored by \e!.
   Currently unsupported.
   .Ss \&troff
   Force troff mode.
   This is a groff extension and currently ignored.
   .Ss \&TS
   Begin a table, which formats input in aligned rows and columns.
   See
   .Xr tbl 7
   for a description of the tbl language.
   .Ss \&uf
   Globally set the underline font.
   Currently ignored.
   .Ss \&ul
   Underline.
   Currently ignored.
   .Ss \&unformat
   Unformat spaces and tabs in a diversion.
   Currently unsupported.
   .Ss \&unwatch
   Disable notification for string or macro.
   This is a Heirloom extension and currently ignored.
   .Ss \&unwatchn
   Disable notification for register.
   This is a Heirloom extension and currently ignored.
   .Ss \&vpt
   Enable or disable vertical position traps.
   This is a groff extension and currently ignored.
   .Ss \&vs
   Change vertical spacing.
   Currently ignored.
   .Ss \&warn
   Set warning level.
   Currently ignored.
   .Ss \&warnscale
   Set the scaling indicator used in warnings.
   This is a groff extension and currently ignored.
   .Ss \&watch
   Notify on change of string or macro.
   This is a Heirloom extension and currently ignored.
   .Ss \&watchlength
   On change, report the contents of macros and strings
   up to the sepcified length.
   This is a Heirloom extension and currently ignored.
   .Ss \&watchn
   Notify on change of register.
   This is a Heirloom extension and currently ignored.
   .Ss \&wh
   Set a page location trap.
   Currently unsupported.
   .Ss \&while
   Repeated execution while a condition is true.
   Currently unsupported.
   .Ss \&write
   Write to an open file.
   Ignored because insecure.
   .Ss \&writec
   Write to an open file without appending a newline.
   Ignored because insecure.
   .Ss \&writem
   Write macro or string to an open file.
   Ignored because insecure.
   .Ss \&xflag
   Set the extension level.
   This is a Heirloom extension and currently ignored.
   .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 precendence; evaluation proceeds from left to right,
   except when subexpressions are enclosed in parantheses.
   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 number Ns \(aq
   Horizontal motion; ignored by
   .Xr mandoc 1 .
   .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 number Ns Oo Ar c Oc Ns \(aq
   Horizontal line drawing function; ignored by
   .Xr mandoc 1 .
   .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 \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
   For security reasons,
   .Xr mandoc 1
   never reads or writes external files except via
   .Sx \&so
   requests with safe relative paths.
   .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
 .Cm nS  .Sq u
 request to  scaling unit is the default terminal unit.
 .Sx \&nr  In traditional troff systems, this unit changes depending on the
 is only compatible with OpenBSD's groff.  output media.
 .It  .It
 Historic groff did not accept white-space buffering the custom END tag  Width measurements are implemented in a crude way
 for the  and often yield wrong results.
 .Sx \&ig  Explicit movement requests and escapes are ignored.
 macro.  
 .It  .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  The
 .Sx \&if  .Qq \(aq
 and family would print funny white-spaces with historic groff when  macro control character does not suppress output line breaks.
 depending on next-line syntax.  .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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