man/man7/man.7

.\"	$OpenBSD: man.7,v 1.29 2012/06/20 21:37:32 schwarze Exp $
.\"
.\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
.\" Copyright (c) 2011 Ingo Schwarze <schwarze@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: June 20 2012 $
.Dt MAN 7
.Os
.Sh NAME
.Nm man
.Nd legacy formatting language for manual pages
.Sh DESCRIPTION
Traditionally, the
.Nm man
language has been used to write
.Ux
manuals for the
.Xr man 1
utility.
It supports limited control of presentational details like fonts,
indentation and spacing.
This reference document describes the structure of manual pages
and the syntax and usage of the man language.
.Pp
.Bf -emphasis
Do not use
.Nm
to write your manuals:
.Ef
It lacks support for semantic markup.
Use the
.Xr mdoc 7
language, instead.
.Pp
In a
.Nm
document, lines beginning with the control character
.Sq \&.
are called
.Dq macro lines .
The first word is the macro name.
It usually consists of two capital letters.
For a list of available macros, see
.Sx MACRO OVERVIEW .
The words following the macro name are arguments to the macro.
.Pp
Lines not beginning with the control character are called
.Dq text lines .
They provide free-form text to be printed; the formatting of the text
depends on the respective processing context:
.Bd -literal -offset indent
\&.SH Macro lines change control state.
Text lines are interpreted within the current state.
.Ed
.Pp
Many aspects of the basic syntax of the
.Nm
language are based on the
.Xr roff 7
language; see the
.Em LANGUAGE SYNTAX
and
.Em MACRO SYNTAX
sections in the
.Xr roff 7
manual for details, in particular regarding
comments, escape sequences, whitespace, and quoting.
.Sh MANUAL STRUCTURE
Each
.Nm
document must contain the
.Sx \&TH
macro describing the document's section and title.
It may occur anywhere in the document, although conventionally it
appears as the first macro.
.Pp
Beyond
.Sx \&TH ,
at least one macro or text line must appear in the document.
.Pp
The following is a well-formed skeleton
.Nm
file for a utility
.Qq progname :
.Bd -literal -offset indent
\&.TH PROGNAME 1 2009-10-10
\&.SH NAME
\efBprogname\efR \e(en a description goes here
\&.\e\(dq .SH LIBRARY
\&.\e\(dq For sections 2 & 3 only.
\&.\e\(dq Not used in OpenBSD.
\&.SH SYNOPSIS
\efBprogname\efR [\efB\e-options\efR] arguments...
\&.SH DESCRIPTION
The \efBfoo\efR utility processes files...
\&.\e\(dq .SH IMPLEMENTATION NOTES
\&.\e\(dq Not used in OpenBSD.
\&.\e\(dq .SH RETURN VALUES
\&.\e\(dq For sections 2, 3, & 9 only.
\&.\e\(dq .SH ENVIRONMENT
\&.\e\(dq For sections 1, 6, 7, & 8 only.
\&.\e\(dq .SH FILES
\&.\e\(dq .SH EXIT STATUS
\&.\e\(dq For sections 1, 6, & 8 only.
\&.\e\(dq .SH EXAMPLES
\&.\e\(dq .SH DIAGNOSTICS
\&.\e\(dq For sections 1, 4, 6, 7, & 8 only.
\&.\e\(dq .SH ERRORS
\&.\e\(dq For sections 2, 3, & 9 only.
\&.\e\(dq .SH SEE ALSO
\&.\e\(dq .BR foo ( 1 )
\&.\e\(dq .SH STANDARDS
\&.\e\(dq .SH HISTORY
\&.\e\(dq .SH AUTHORS
\&.\e\(dq .SH CAVEATS
\&.\e\(dq .SH BUGS
\&.\e\(dq .SH SECURITY CONSIDERATIONS
\&.\e\(dq Not used in OpenBSD.
.Ed
.Pp
The sections in a
.Nm
document are conventionally ordered as they appear above.
Sections should be composed as follows:
.Bl -ohang -offset indent
.It Em NAME
The name(s) and a short description of the documented material.
The syntax for this is generally as follows:
.Pp
.D1 \efBname\efR \e(en description
.It Em LIBRARY
The name of the library containing the documented material, which is
assumed to be a function in a section 2 or 3 manual.
For functions in the C library, this may be as follows:
.Pp
.D1 Standard C Library (libc, -lc)
.It Em SYNOPSIS
Documents the utility invocation syntax, function call syntax, or device
configuration.
.Pp
For the first, utilities (sections 1, 6, and 8), this is
generally structured as follows:
.Pp
.D1 \efBname\efR [-\efBab\efR] [-\efBc\efR\efIarg\efR] \efBpath\efR...
.Pp
For the second, function calls (sections 2, 3, 9):
.Pp
.D1 \&.B char *name(char *\efIarg\efR);
.Pp
And for the third, configurations (section 4):
.Pp
.D1 \&.B name* at cardbus ? function ?
.Pp
Manuals not in these sections generally don't need a
.Em SYNOPSIS .
.It Em DESCRIPTION
This expands upon the brief, one-line description in
.Em NAME .
It usually contains a break-down of the options (if documenting a
command).
.It Em IMPLEMENTATION NOTES
Implementation-specific notes should be kept here.
This is useful when implementing standard functions that may have side
effects or notable algorithmic implications.
.It Em RETURN VALUES
This section documents the return values of functions in sections 2, 3, and 9.
.It Em ENVIRONMENT
Documents any usages of environment variables, e.g.,
.Xr environ 7 .
.It Em FILES
Documents files used.
It's helpful to document both the file name and a short description of how
the file is used (created, modified, etc.).
.It Em EXIT STATUS
This section documents the command exit status for
section 1, 6, and 8 utilities.
Historically, this information was described in
.Em DIAGNOSTICS ,
a practise that is now discouraged.
.It Em EXAMPLES
Example usages.
This often contains snippets of well-formed,
well-tested invocations.
Make sure that examples work properly!
.It Em DIAGNOSTICS
Documents error conditions.
This is most useful in section 4 manuals.
Historically, this section was used in place of
.Em EXIT STATUS
for manuals in sections 1, 6, and 8; however, this practise is
discouraged.
.It Em ERRORS
Documents error handling in sections 2, 3, and 9.
.It Em SEE ALSO
References other manuals with related topics.
This section should exist for most manuals.
.Pp
.D1 \&.BR bar \&( 1 \&),
.Pp
Cross-references should conventionally be ordered
first by section, then alphabetically.
.It Em STANDARDS
References any standards implemented or used, such as
.Pp
.D1 IEEE Std 1003.2 (\e(lqPOSIX.2\e(rq)
.Pp
If not adhering to any standards, the
.Em HISTORY
section should be used.
.It Em HISTORY
A brief history of the subject, including where support first appeared.
.It Em AUTHORS
Credits to the person or persons who wrote the code and/or documentation.
Authors should generally be noted by both name and email address.
.It Em CAVEATS
Common misuses and misunderstandings should be explained
in this section.
.It Em BUGS
Known bugs, limitations, and work-arounds should be described
in this section.
.It Em SECURITY CONSIDERATIONS
Documents any security precautions that operators should consider.
.El
.Sh MACRO OVERVIEW
This overview is sorted such that macros of similar purpose are listed
together, to help find the best macro for any given purpose.
Deprecated macros are not included in the overview, but can be found
in the alphabetical reference below.
.Ss Page header and footer meta-data
.Bl -column "PP, LP, P" description
.It Sx TH Ta set the title: Ar title section date Op Ar source Op Ar volume
.It Sx AT Ta display AT&T UNIX version in the page footer (<= 1 argument)
.It Sx UC Ta display BSD version in the page footer (<= 1 argument)
.El
.Ss Sections and paragraphs
.Bl -column "PP, LP, P" description
.It Sx SH Ta section header (one line)
.It Sx SS Ta subsection header (one line)
.It Sx PP , LP , P Ta start an undecorated paragraph (no arguments)
.It Sx RS , RE Ta reset the left margin: Op Ar width
.It Sx IP Ta indented paragraph: Op Ar head Op Ar width
.It Sx TP Ta tagged paragraph: Op Ar width
.It Sx HP Ta hanged paragraph: Op Ar width
.It Sx \&br Ta force output line break in text mode (no arguments)
.It Sx \&sp Ta force vertical space: Op Ar height
.It Sx fi , nf Ta fill mode and no-fill mode (no arguments)
.It Sx in Ta additional indent: Op Ar width
.El
.Ss Physical markup
.Bl -column "PP, LP, P" description
.It Sx B Ta boldface font
.It Sx I Ta italic font
.It Sx R Ta roman (default) font
.It Sx SB Ta small boldface font
.It Sx SM Ta small roman font
.It Sx BI Ta alternate between boldface and italic fonts
.It Sx BR Ta alternate between boldface and roman fonts
.It Sx IB Ta alternate between italic and boldface fonts
.It Sx IR Ta alternate between italic and roman fonts
.It Sx RB Ta alternate between roman and boldface fonts
.It Sx RI Ta alternate between roman and italic fonts
.El
.Sh MACRO REFERENCE
This section is a canonical reference to all macros, arranged
alphabetically.
For the scoping of individual macros, see
.Sx MACRO SYNTAX .
.Ss \&AT
Sets the volume for the footer for compatibility with man pages from
.Tn AT&T UNIX
releases.
The optional arguments specify which release it is from.
.Ss \&B
Text is rendered in bold face.
.Pp
See also
.Sx \&I
and
.Sx \&R .
.Ss \&BI
Text is rendered alternately in bold face and italic.
Thus,
.Sq .BI this word and that
causes
.Sq this
and
.Sq and
to render in bold face, while
.Sq word
and
.Sq that
render in italics.
Whitespace between arguments is omitted in output.
.Pp
Examples:
.Pp
.Dl \&.BI bold italic bold italic
.Pp
The output of this example will be emboldened
.Dq bold
and italicised
.Dq italic ,
with spaces stripped between arguments.
.Pp
See also
.Sx \&IB ,
.Sx \&BR ,
.Sx \&RB ,
.Sx \&RI ,
and
.Sx \&IR .
.Ss \&BR
Text is rendered alternately in bold face and roman (the default font).
Whitespace between arguments is omitted in output.
.Pp
See
.Sx \&BI
for an equivalent example.
.Pp
See also
.Sx \&BI ,
.Sx \&IB ,
.Sx \&RB ,
.Sx \&RI ,
and
.Sx \&IR .
.Ss \&DT
Has no effect.
Included for compatibility.
.Ss \&EE
This is a non-standard GNU extension, included only for compatibility.
In
.Xr mandoc 1 ,
it does the same as
.Sx \&fi .
.Ss \&EX
This is a non-standard GNU extension, included only for compatibility.
In
.Xr mandoc 1 ,
it does the same as
.Sx \&nf .
.Ss \&HP
Begin a paragraph whose initial output line is left-justified, but
subsequent output lines are indented, with the following syntax:
.Bd -filled -offset indent
.Pf \. Sx \&HP
.Op Cm width
.Ed
.Pp
The
.Cm width
argument is a
.Xr roff 7
scaling width.
If specified, it's saved for later paragraph left-margins; if unspecified, the
saved or default width is used.
.Pp
See also
.Sx \&IP ,
.Sx \&LP ,
.Sx \&P ,
.Sx \&PP ,
and
.Sx \&TP .
.Ss \&I
Text is rendered in italics.
.Pp
See also
.Sx \&B
and
.Sx \&R .
.Ss \&IB
Text is rendered alternately in italics and bold face.
Whitespace between arguments is omitted in output.
.Pp
See
.Sx \&BI
for an equivalent example.
.Pp
See also
.Sx \&BI ,
.Sx \&BR ,
.Sx \&RB ,
.Sx \&RI ,
and
.Sx \&IR .
.Ss \&IP
Begin an indented paragraph with the following syntax:
.Bd -filled -offset indent
.Pf \. Sx \&IP
.Op Cm head Op Cm width
.Ed
.Pp
The
.Cm width
argument is a
.Xr roff 7
scaling width defining the left margin.
It's saved for later paragraph left-margins; if unspecified, the saved or
default width is used.
.Pp
The
.Cm head
argument is used as a leading term, flushed to the left margin.
This is useful for bulleted paragraphs and so on.
.Pp
See also
.Sx \&HP ,
.Sx \&LP ,
.Sx \&P ,
.Sx \&PP ,
and
.Sx \&TP .
.Ss \&IR
Text is rendered alternately in italics and roman (the default font).
Whitespace between arguments is omitted in output.
.Pp
See
.Sx \&BI
for an equivalent example.
.Pp
See also
.Sx \&BI ,
.Sx \&IB ,
.Sx \&BR ,
.Sx \&RB ,
and
.Sx \&RI .
.Ss \&LP
Begin an undecorated paragraph.
The scope of a paragraph is closed by a subsequent paragraph,
sub-section, section, or end of file.
The saved paragraph left-margin width is reset to the default.
.Pp
See also
.Sx \&HP ,
.Sx \&IP ,
.Sx \&P ,
.Sx \&PP ,
and
.Sx \&TP .
.Ss \&OP
Optional command-line argument.
This is a non-standard GNU extension, included only for compatibility.
It has the following syntax:
.Bd -filled -offset indent
.Pf \. Sx \&OP
.Cm key Op Cm value
.Ed
.Pp
The
.Cm key
is usually a command-line flag and
.Cm value
its argument.
.Ss \&P
Synonym for
.Sx \&LP .
.Pp
See also
.Sx \&HP ,
.Sx \&IP ,
.Sx \&LP ,
.Sx \&PP ,
and
.Sx \&TP .
.Ss \&PP
Synonym for
.Sx \&LP .
.Pp
See also
.Sx \&HP ,
.Sx \&IP ,
.Sx \&LP ,
.Sx \&P ,
and
.Sx \&TP .
.Ss \&R
Text is rendered in roman (the default font).
.Pp
See also
.Sx \&I
and
.Sx \&B .
.Ss \&RB
Text is rendered alternately in roman (the default font) and bold face.
Whitespace between arguments is omitted in output.
.Pp
See
.Sx \&BI
for an equivalent example.
.Pp
See also
.Sx \&BI ,
.Sx \&IB ,
.Sx \&BR ,
.Sx \&RI ,
and
.Sx \&IR .
.Ss \&RE
Explicitly close out the scope of a prior
.Sx \&RS .
The default left margin is restored to the state of the original
.Sx \&RS
invocation.
.Ss \&RI
Text is rendered alternately in roman (the default font) and italics.
Whitespace between arguments is omitted in output.
.Pp
See
.Sx \&BI
for an equivalent example.
.Pp
See also
.Sx \&BI ,
.Sx \&IB ,
.Sx \&BR ,
.Sx \&RB ,
and
.Sx \&IR .
.Ss \&RS
Temporarily reset the default left margin.
This has the following syntax:
.Bd -filled -offset indent
.Pf \. Sx \&RS
.Op Cm width
.Ed
.Pp
The
.Cm width
argument is a
.Xr roff 7
scaling width.
If not specified, the saved or default width is used.
.Pp
See also
.Sx \&RE .
.Ss \&SB
Text is rendered in small size (one point smaller than the default font)
bold face.
.Ss \&SH
Begin a section.
The scope of a section is only closed by another section or the end of
file.
The paragraph left-margin width is reset to the default.
.Ss \&SM
Text is rendered in small size (one point smaller than the default
font).
.Ss \&SS
Begin a sub-section.
The scope of a sub-section is closed by a subsequent sub-section,
section, or end of file.
The paragraph left-margin width is reset to the default.
.Ss \&TH
Sets the title of the manual page with the following syntax:
.Bd -filled -offset indent
.Pf \. Sx \&TH
.Ar title section date
.Op Ar source Op Ar volume
.Ed
.Pp
Conventionally, the document
.Ar title
is given in all caps.
The recommended
.Ar date
format is
.Sy YYYY-MM-DD
as specified in the ISO-8601 standard;
if the argument does not conform, it is printed verbatim.
If the
.Ar date
is empty or not specified, the current date is used.
The optional
.Ar source
string specifies the organisation providing the utility.
The
.Ar volume
string replaces the default rendered volume, which is dictated by the
manual section.
.Pp
Examples:
.Pp
.Dl \&.TH CVS 5 "1992-02-12" GNU
.Ss \&TP
Begin a paragraph where the head, if exceeding the indentation width, is
followed by a newline; if not, the body follows on the same line after a
buffer to the indentation width.
Subsequent output lines are indented.
The syntax is as follows:
.Bd -filled -offset indent
.Pf \. Sx \&TP
.Op Cm width
.Ed
.Pp
The
.Cm width
argument is a
.Xr roff 7
scaling width.
If specified, it's saved for later paragraph left-margins; if
unspecified, the saved or default width is used.
.Pp
See also
.Sx \&HP ,
.Sx \&IP ,
.Sx \&LP ,
.Sx \&P ,
and
.Sx \&PP .
.Ss \&UC
Sets the volume for the footer for compatibility with man pages from
BSD releases.
The optional first argument specifies which release it is from.
.Ss \&br
Breaks the current line.
Consecutive invocations have no further effect.
.Pp
See also
.Sx \&sp .
.Ss \&fi
End literal mode begun by
.Sx \&nf .
.Ss \&in
Indent relative to the current indentation:
.Pp
.D1 Pf \. Sx \&in Op Cm width
.Pp
If
.Cm width
is signed, the new offset is relative.
Otherwise, it is absolute.
This value is reset upon the next paragraph, section, or sub-section.
.Ss \&na
Don't align to the right margin.
.Ss \&nf
Begin literal mode: all subsequent free-form lines have their end of
line boundaries preserved.
May be ended by
.Sx \&fi .
Literal mode is implicitly ended by
.Sx \&SH
or
.Sx \&SS .
.Ss \&sp
Insert vertical spaces into output with the following syntax:
.Bd -filled -offset indent
.Pf \. Sx \&sp
.Op Cm height
.Ed
.Pp
The
.Cm height
argument is a scaling width as described in
.Xr roff 7 .
If 0, this is equivalent to the
.Sx \&br
macro.
Defaults to 1, if unspecified.
.Pp
See also
.Sx \&br .
.Sh MACRO SYNTAX
The
.Nm
macros are classified by scope: line scope or block scope.
Line macros are only scoped to the current line (and, in some
situations, the subsequent line).
Block macros are scoped to the current line and subsequent lines until
closed by another block macro.
.Ss Line Macros
Line macros are generally scoped to the current line, with the body
consisting of zero or more arguments.
If a macro is scoped to the next line and the line arguments are empty,
the next line, which must be text, is used instead.
Thus:
.Bd -literal -offset indent
\&.I
foo
.Ed
.Pp
is equivalent to
.Sq \&.I foo .
If next-line macros are invoked consecutively, only the last is used.
If a next-line macro is followed by a non-next-line macro, an error is
raised, except for
.Sx \&br ,
.Sx \&sp ,
and
.Sx \&na .
.Pp
The syntax is as follows:
.Bd -literal -offset indent
\&.YO \(lBbody...\(rB
\(lBbody...\(rB
.Ed
.Bl -column "MacroX" "ArgumentsX" "ScopeXXXXX" "CompatX" -offset indent
.It Em Macro Ta Em Arguments Ta Em Scope     Ta Em Notes
.It Sx \&AT  Ta    <=1       Ta    current   Ta    \&
.It Sx \&B   Ta    n         Ta    next-line Ta    \&
.It Sx \&BI  Ta    n         Ta    current   Ta    \&
.It Sx \&BR  Ta    n         Ta    current   Ta    \&
.It Sx \&DT  Ta    0         Ta    current   Ta    \&
.It Sx \&I   Ta    n         Ta    next-line Ta    \&
.It Sx \&IB  Ta    n         Ta    current   Ta    \&
.It Sx \&IR  Ta    n         Ta    current   Ta    \&
.It Sx \&OP  Ta    0, 1      Ta    current   Ta    compat
.It Sx \&R   Ta    n         Ta    next-line Ta    \&
.It Sx \&RB  Ta    n         Ta    current   Ta    \&
.It Sx \&RI  Ta    n         Ta    current   Ta    \&
.It Sx \&SB  Ta    n         Ta    next-line Ta    \&
.It Sx \&SM  Ta    n         Ta    next-line Ta    \&
.It Sx \&TH  Ta    >1, <6    Ta    current   Ta    \&
.It Sx \&UC  Ta    <=1       Ta    current   Ta    \&
.It Sx \&br  Ta    0         Ta    current   Ta    compat
.It Sx \&fi  Ta    0         Ta    current   Ta    compat
.It Sx \&in  Ta    1         Ta    current   Ta    compat
.It Sx \&na  Ta    0         Ta    current   Ta    compat
.It Sx \&nf  Ta    0         Ta    current   Ta    compat
.It Sx \&sp  Ta    1         Ta    current   Ta    compat
.El
.Pp
Macros marked as
.Qq compat
are included for compatibility with the significant corpus of existing
manuals that mix dialects of roff.
These macros should not be used for portable
.Nm
manuals.
.Ss Block Macros
Block macros comprise a head and body.
As with in-line macros, the head is scoped to the current line and, in
one circumstance, the next line (the next-line stipulations as in
.Sx Line Macros
apply here as well).
.Pp
The syntax is as follows:
.Bd -literal -offset indent
\&.YO \(lBhead...\(rB
\(lBhead...\(rB
\(lBbody...\(rB
.Ed
.Pp
The closure of body scope may be to the section, where a macro is closed
by
.Sx \&SH ;
sub-section, closed by a section or
.Sx \&SS ;
part, closed by a section, sub-section, or
.Sx \&RE ;
or paragraph, closed by a section, sub-section, part,
.Sx \&HP ,
.Sx \&IP ,
.Sx \&LP ,
.Sx \&P ,
.Sx \&PP ,
or
.Sx \&TP .
No closure refers to an explicit block closing macro.
.Pp
As a rule, block macros may not be nested; thus, calling a block macro
while another block macro scope is open, and the open scope is not
implicitly closed, is syntactically incorrect.
.Bl -column "MacroX" "ArgumentsX" "Head ScopeX" "sub-sectionX" "compatX" -offset indent
.It Em Macro Ta Em Arguments Ta Em Head Scope Ta Em Body Scope  Ta Em Notes
.It Sx \&HP  Ta    <2        Ta    current    Ta    paragraph   Ta    \&
.It Sx \&IP  Ta    <3        Ta    current    Ta    paragraph   Ta    \&
.It Sx \&LP  Ta    0         Ta    current    Ta    paragraph   Ta    \&
.It Sx \&P   Ta    0         Ta    current    Ta    paragraph   Ta    \&
.It Sx \&PP  Ta    0         Ta    current    Ta    paragraph   Ta    \&
.It Sx \&RE  Ta    0         Ta    current    Ta    none        Ta    compat
.It Sx \&RS  Ta    1         Ta    current    Ta    part        Ta    compat
.It Sx \&SH  Ta    >0        Ta    next-line  Ta    section     Ta    \&
.It Sx \&SS  Ta    >0        Ta    next-line  Ta    sub-section Ta    \&
.It Sx \&TP  Ta    n         Ta    next-line  Ta    paragraph   Ta    \&
.El
.Pp
Macros marked
.Qq compat
are as mentioned in
.Sx Line Macros .
.Pp
If a block macro is next-line scoped, it may only be followed by in-line
macros for decorating text.
.Ss Font handling
In
.Nm
documents, both
.Sx Physical markup
macros and
.Xr roff 7
.Ql \ef
font escape sequences can be used to choose fonts.
In text lines, the effect of manual font selection by escape sequences
only lasts until the next macro invocation; in macro lines, it only lasts
until the end of the macro scope.
Note that macros like
.Sx \&BR
open and close a font scope for each argument.
.Sh COMPATIBILITY
This section documents areas of questionable portability between
implementations of the
.Nm
language.
.Pp
.Bl -dash -compact
.It
Do not depend on
.Sx \&SH
or
.Sx \&SS
to close out a literal context opened with
.Sx \&nf .
This behaviour may not be portable.
.It
In quoted literals, GNU troff allowed pair-wise double-quotes to produce
a standalone double-quote in formatted output.
It is not known whether this behaviour is exhibited by other formatters.
.It
troff suppresses a newline before
.Sq \(aq
macro output; in mandoc, it is an alias for the standard
.Sq \&.
control character.
.It
The
.Sq \eh
.Pq horizontal position ,
.Sq \ev
.Pq vertical position ,
.Sq \em
.Pq text colour ,
.Sq \eM
.Pq text filling colour ,
.Sq \ez
.Pq zero-length character ,
.Sq \ew
.Pq string length ,
.Sq \ek
.Pq horizontal position marker ,
.Sq \eo
.Pq text overstrike ,
and
.Sq \es
.Pq text size
escape sequences are all discarded in mandoc.
.It
The
.Sq \ef
scaling unit is accepted by mandoc, but rendered as the default unit.
.It
The
.Sx \&sp
macro does not accept negative values in mandoc.
In GNU troff, this would result in strange behaviour.
.It
In page header lines, GNU troff versions up to and including 1.21
only print
.Ar volume
names explicitly specified in the
.Sx \&TH
macro; mandoc and newer groff print the default volume name
corresponding to the
.Ar section
number when no
.Ar volume
is given, like in
.Xr mdoc 7 .
.El
.Pp
The
.Sx OP
macro is part of the extended
.Nm
macro set, and may not be portable to non-GNU troff implementations.
.Sh SEE ALSO
.Xr man 1 ,
.Xr mandoc 1 ,
.Xr eqn 7 ,
.Xr mandoc_char 7 ,
.Xr mdoc 7 ,
.Xr roff 7 ,
.Xr tbl 7
.Sh HISTORY
The
.Nm
language first appeared as a macro package for the roff typesetting
system in
.At v7 .
It was later rewritten by James Clark as a macro package for groff.
Eric S. Raymond wrote the extended
.Nm
macros for groff in 2007.
The stand-alone implementation that is part of the
.Xr mandoc 1
utility written by Kristaps Dzonsons appeared in
.Ox 4.6 .
.Sh AUTHORS
This
.Nm
reference was written by
.An Kristaps Dzonsons ,
.Mt kristaps@bsd.lv .
.Sh CAVEATS
Do not use this language.
Use
.Xr mdoc 7 ,
instead.