.\"	$OpenBSD: man.7,v 1.17 2011/03/07 01:35:33 schwarze Exp $
.\"
.\" Copyright (c) 2009, 2010 Kristaps Dzonsons <kristaps@bsd.lv>
.\"
.\" 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.
.\"
.\" 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: March 7 2011 $
.Dt MAN 7
.Os
.Sh NAME
.Nm man
.Nd man language reference
.Sh DESCRIPTION
The
.Nm man
language was historically used to format
.Ux
manuals.
This reference document describes its syntax, structure, and usage.
.Pp
.Bf -emphasis
Do not use
.Nm
to write your manuals.
.Ef
Use the
.Xr mdoc 7
language, instead.
.Pp
A
.Nm
document follows simple rules:  lines beginning with the control
character
.Sq \&.
are parsed for macros.
Other lines are interpreted within the scope of
prior macros:
.Bd -literal -offset indent
\&.SH Macro lines change control state.
Other lines are interpreted within the current state.
.Ed
.Sh INPUT ENCODING
.Nm
documents may contain only graphable 7-bit ASCII characters, the
space character, and the tab character.
.Pp
Blank lines are acceptable; where found, the output will assert a
vertical space.
.Pp
If the first character of a line is a space, that line is printed
with a leading newline.
.Ss Comments
Text following a
.Sq \e\*q ,
whether in a macro or free-form text line, is ignored to the end of
line.
A macro line with only a control character and comment escape,
.Sq \&.\e\*q ,
is also ignored.
Macro lines with only a control character and optionally whitespace are
stripped from input.
.Ss Special Characters
Special characters may occur in both macro and free-form 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.
See
.Xr mandoc_char 7
for a complete list.
Examples include
.Sq \e(em
.Pq em-dash
and
.Sq \ee
.Pq back-slash .
.Ss Text Decoration
Terms may be text-decorated using the
.Sq \ef
escape followed by an indicator: B (bold), I (italic), R (Roman), or P
(revert to previous mode):
.Pp
.D1 \efBbold\efR \efIitalic\efP
.Pp
A numerical representation 3, 2, or 1 (bold, italic, and Roman,
respectively) may be used instead.
A text decoration is only valid, if specified in free-form text, until
the next macro invocation; if specified within a macro, it's only valid
until the macro closes scope.
Note that macros like
.Sx \&BR
open and close a font scope with each argument.
.Pp
The
.Sq \ef
attribute is forgotten when entering or exiting a macro block.
.Ss Whitespace
Whitespace consists of the space character.
In free-form lines, whitespace is preserved within a line; unescaped
trailing spaces are stripped from input (unless in a literal context).
Blank free-form lines, which may include spaces, are permitted and
rendered as an empty line.
.Pp
In macro lines, whitespace delimits arguments and is discarded.
If arguments are quoted, whitespace within the quotes is retained.
.Ss Scaling Widths
Many macros support scaled widths for their arguments, such as
stipulating a two-inch paragraph indentation with the following:
.Bd -literal -offset indent
\&.HP 2i
.Ed
.Pp
The syntax for scaled widths is
.Sq Li [+-]?[0-9]*.[0-9]*[:unit:]? ,
where a decimal must be preceded or proceeded by at least one digit.
Negative numbers, while accepted, are truncated to zero.
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
synonym for
.Sq u
.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
.It M
mini-em (~1/100 em)
.El
.Pp
Using anything other than
.Sq m ,
.Sq n ,
.Sq u ,
or
.Sq v
is necessarily non-portable across output media.
.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.
.Em Note :
this differs from
.Xr mdoc 7 ,
which, if a unit is not provided, will instead interpret the string as
literal text.
.Ss Sentence Spacing
When composing a manual, make sure that sentences end at the end of
a line.
By doing so, front-ends 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 .
.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 node must appear in the document.
Documents are generally structured as follows:
.Bd -literal -offset indent
\&.TH FOO 1 2009-10-10
\&.SH NAME
\efBfoo\efR \e(en a description goes here
\&.\e\*q .SH LIBRARY
\&.\e\*q For sections 2 & 3 only.
\&.\e\*q Not used in OpenBSD.
\&.SH SYNOPSIS
\efBfoo\efR [\efB\e-options\efR] arguments...
\&.SH DESCRIPTION
The \efBfoo\efR utility processes files...
\&.\e\*q .SH IMPLEMENTATION NOTES
\&.\e\*q Not used in OpenBSD.
\&.\e\*q .SH RETURN VALUES
\&.\e\*q For sections 2, 3, & 9 only.
\&.\e\*q .SH ENVIRONMENT
\&.\e\*q For sections 1, 6, 7, & 8 only.
\&.\e\*q .SH FILES
\&.\e\*q .SH EXIT STATUS
\&.\e\*q For sections 1, 6, & 8 only.
\&.\e\*q .SH EXAMPLES
\&.\e\*q .SH DIAGNOSTICS
\&.\e\*q For sections 1, 4, 6, 7, & 8 only.
\&.\e\*q .SH ERRORS
\&.\e\*q For sections 2, 3, & 9 only.
\&.\e\*q .SH SEE ALSO
\&.\e\*q .BR foo ( 1 )
\&.\e\*q .SH STANDARDS
\&.\e\*q .SH HISTORY
\&.\e\*q .SH AUTHORS
\&.\e\*q .SH CAVEATS
\&.\e\*q .SH BUGS
\&.\e\*q .SH SECURITY CONSIDERATIONS
\&.\e\*q 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 SYNTAX
Macros are one to three characters in length and begin with a
control character,
.Sq \&. ,
at the beginning of the line.
The
.Sq \(aq
macro control character is also accepted.
An arbitrary amount of whitespace (spaces or tabs) may sit between the
control character and the macro name.
Thus, the following are equivalent:
.Bd -literal -offset indent
\&.PP
\&.\ \ \ PP
.Ed
.Pp
To include space characters in macro arguments, arguments may be quoted;
see the
.Sq MACRO SYNTAX
section in the
.Xr roff 7
manual for details.
.Pp
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
.Pp
.Bl -column -compact -offset indent "MacroX" "ArgumentsX" "ScopeXXXXX" "CompatX"
.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 \&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.
.Pp
.Bl -column -compact -offset indent "MacroX" "ArgumentsX" "Head ScopeX" "sub-sectionX" "compatX"
.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.
.Sh 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 \&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 must conform to
.Sx Scaling Widths .
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 defines the width of the left margin and is defined by
.Sx Scaling Widths .
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 \&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 .
.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
Begin a part setting the left margin.
The left margin controls the offset, following an initial indentation,
to un-indented text such as that of
.Sx \&PP .
This has the following syntax:
.Bd -filled -offset indent
.Pf \. Sx \&Rs
.Op Cm width
.Ed
.Pp
The
.Cm width
argument must conform to
.Sx Scaling Widths .
If not specified, the saved or default width is used.
.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 must conform to
.Sx Scaling Widths .
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 .
.Ss \&sp
Insert vertical spaces into output with the following syntax:
.Bd -filled -offset indent
.Pf \. Sx \&sp
.Op Cm height
.Ed
.Pp
Insert
.Cm height
spaces, which must conform to
.Sx Scaling Widths .
If 0, this is equivalent to the
.Sx \&br
macro.
Defaults to 1, if unspecified.
.Pp
See also
.Sx \&br .
.Sh COMPATIBILITY
This section documents areas of questionable portability between
implementations of the
.Nm
language.
.Pp
.Bl -dash -compact
.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.
.El
.Sh SEE ALSO
.Xr man 1 ,
.Xr mandoc 1 ,
.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.
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 Aq kristaps@bsd.lv .
.Sh CAVEATS
Do not use this language.
Use
.Xr mdoc 7 ,
instead.