.\" $Id$
.\"
.\" Copyright (c) 2010, 2011, 2012 Kristaps Dzonsons <kristaps@bsd.lv>
.\" Copyright (c) 2010, 2011, 2013, 2014 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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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate$
.Dt ROFF 7
.Os
.Sh NAME
.Nm roff
.Nd roff language reference for mandoc
.Sh DESCRIPTION
The
.Nm roff
language is a general purpose text formatting language.
Since traditional implementations of 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
utility supports a tiny subset of
.Nm
requests and escapes.
Only these requests and escapes supported by
.Xr mandoc 1
are documented in the present manual,
together with the basic language syntax shared by
.Nm ,
.Xr mdoc 7 ,
and
.Xr man 7 .
For complete
.Nm
manuals, consult the
.Sx SEE ALSO
section.
.Pp
Input lines beginning with the control character
.Sq \&.
are parsed for requests and macros.
Such lines are called
.Dq request lines
or
.Dq macro lines ,
respectively.
Requests change the processing state and manipulate the formatting;
some macros also define the document structure and produce formatted
output.
The single quote
.Pq Qq \(aq
is accepted as an alternative control character,
treated by
.Xr mandoc 1
just like
.Ql \&.
.Pp
Lines not beginning with control characters are called
.Dq text lines .
They provide free-form text to be printed; the formatting of the text
depends on the respective processing context.
.Sh LANGUAGE SYNTAX
.Nm
documents may contain only graphable 7-bit ASCII characters, the space
character, and, in certain circumstances, the tab character.
The backslash character
.Sq \e
indicates the start of an escape sequence, used for example for
.Sx Comments ,
.Sx Special Characters ,
.Sx Predefined Strings ,
and
user-defined strings defined using the
.Sx ds
request.
For a listing of escape sequences, consult the
.Sx ESCAPE SEQUENCE REFERENCE
below.
.Ss Comments
Text following an escaped double-quote
.Sq \e\(dq ,
whether in a request, macro, or text line, is ignored to the end of the line.
A request line beginning with a control character and comment escape
.Sq \&.\e\(dq
is also ignored.
Furthermore, request lines with only a control character and optional
trailing whitespace are stripped from input.
.Pp
Examples:
.Bd -literal -offset indent -compact
\&.\e\(dq This is a comment line.
\&.\e\(dq The next line is ignored:
\&.
\&.Sh EXAMPLES \e\(dq This is a comment, too.
\&example text \e\(dq And so is this.
.Ed
.Ss Special Characters
Special characters are used to encode special glyphs and are rendered
differently across output media.
They may occur in request, macro, and text lines.
Sequences begin with the escape character
.Sq \e
followed by either an open-parenthesis
.Sq \&(
for two-character sequences; an open-bracket
.Sq \&[
for n-character sequences (terminated at a close-bracket
.Sq \&] ) ;
or a single one character sequence.
.Pp
Examples:
.Bl -tag -width Ds -offset indent -compact
.It Li \e(em
Two-letter em dash escape.
.It Li \ee
One-letter backslash escape.
.El
.Pp
See
.Xr mandoc_char 7
for a complete list.
.Ss Text Decoration
Terms may be text-decorated using the
.Sq \ef
escape followed by an indicator: B (bold), I (italic), R (regular), or P
(revert to previous mode).
A numerical representation 3, 2, or 1 (bold, italic, and regular,
respectively) may be used instead.
The indicator or numerical representative may be preceded by C
(constant-width), which is ignored.
.Pp
The two-character indicator
.Sq BI
requests a font that is both bold and italic.
It may not be portable to old roff implementations.
.Pp
Examples:
.Bl -tag -width Ds -offset indent -compact
.It Li \efBbold\efR
Write in \fBbold\fP, then switch to regular font mode.
.It Li \efIitalic\efP
Write in \fIitalic\fP, then return to previous font mode.
.It Li \ef(BIbold italic\efP
Write in \f(BIbold italic\fP, then return to previous font mode.
.El
.Pp
Text decoration is
.Em not
recommended for
.Xr mdoc 7 ,
which encourages semantic annotation.
.Ss Predefined Strings
Predefined strings, like
.Sx Special Characters ,
mark special output glyphs.
Predefined strings are escaped with the slash-asterisk,
.Sq \e* :
single-character
.Sq \e*X ,
two-character
.Sq \e*(XX ,
and N-character
.Sq \e*[N] .
.Pp
Examples:
.Bl -tag -width Ds -offset indent -compact
.It Li \e*(Am
Two-letter ampersand predefined string.
.It Li \e*q
One-letter double-quote predefined string.
.El
.Pp
Predefined strings are not recommended for use,
as they differ across implementations.
Those supported by
.Xr mandoc 1
are listed in
.Xr mandoc_char 7 .
Manuals using these predefined strings are almost certainly not portable.
.Ss Whitespace
Whitespace consists of the space character.
In text lines, whitespace is preserved within a line.
In request and macro lines, whitespace delimits arguments and is discarded.
.Pp
Unescaped trailing spaces are stripped from text line input unless in a
literal context.
In general, trailing whitespace on any input line is discouraged for
reasons of portability.
In the rare case that a blank character is needed at the end of an
input line, it may be forced by
.Sq \e\ \e& .
.Pp
Literal space characters can be produced in the output
using escape sequences.
In macro lines, they can also be included in arguments using quotation; see
.Sx MACRO SYNTAX
for details.
.Pp
Blank text lines, which may include whitespace, are only permitted
within literal contexts.
If the first character of a text line is a space, that line is printed
with a leading newline.
.Ss Scaling Widths
Many requests and macros support scaled widths for their arguments.
The syntax for a scaled width is
.Sq Li [+-]?[0-9]*.[0-9]*[:unit:] ,
where a decimal must be preceded or followed by at least one digit.
Negative numbers, while accepted, are truncated to zero.
.Pp
The following scaling units are accepted:
.Pp
.Bl -tag -width Ds -offset indent -compact
.It c
centimetre
.It i
inch
.It P
pica (~1/6 inch)
.It p
point (~1/72 inch)
.It f
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.
See
.Sx COMPATIBILITY .
.Pp
If a scaling unit is not provided, the numerical value is interpreted
under the default rules of
.Sq v
for vertical spaces and
.Sq u
for horizontal ones.
.Pp
Examples:
.Bl -tag -width ".Bl -tag -width 2i" -offset indent -compact
.It Li \&.Bl -tag -width 2i
two-inch tagged list indentation in
.Xr mdoc 7
.It Li \&.HP 2i
two-inch tagged list indentation in
.Xr man 7
.It Li \&.sp 2v
two vertical spaces
.El
.Ss Sentence Spacing
Each sentence should terminate at the end of an input line.
By doing this, a formatter will be able to apply the proper amount of
spacing after the end of sentence (unescaped) period, exclamation mark,
or question mark followed by zero or more non-sentence closing
delimiters
.Po
.Sq \&) ,
.Sq \&] ,
.Sq \&' ,
.Sq \&"
.Pc .
.Pp
The proper spacing is also intelligently preserved if a sentence ends at
the boundary of a macro line.
.Pp
Examples:
.Bd -literal -offset indent -compact
Do not end sentences mid-line like this. Instead,
end a sentence like this.
A macro would end like this:
\&.Xr mandoc 1 \&.
.Ed
.Sh REQUEST SYNTAX
A request or macro line consists of:
.Pp
.Bl -enum -compact
.It
the control character
.Sq \&.
or
.Sq \(aq
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
\&.ig end
\&.ig end
\&. ig end
.Ed
.Sh MACRO SYNTAX
Macros are provided by the
.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.
Note that the
.Nm
language defines many more requests not implemented in
.Xr mandoc 1 .
.Ss \&ad
Set line adjustment mode.
This line-scoped request is intended to have one argument to select
normal, left, right, or centre adjustment for subsequent text.
Currently, it is ignored including its arguments,
and the number of arguments is not checked.
.Ss \&am
Append to a macro definition.
The syntax of this request is the same as that of
.Sx \&de .
It is currently ignored by
.Xr mandoc 1 ,
as are its children.
.Ss \&ami
Append to a macro definition, specifying the macro name indirectly.
The syntax of this request is the same as that of
.Sx \&dei .
It is currently ignored by
.Xr mandoc 1 ,
as are its children.
.Ss \&am1
Append to a macro definition, switching roff compatibility mode off
during macro execution.
The syntax of this request is the same as that of
.Sx \&de1 .
It is currently ignored by
.Xr mandoc 1 ,
as are its children.
.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 \&cc
Changes 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.
This line-scoped request is intended to take one integer argument,
specifying how many lines to center.
Currently, it is ignored including its arguments, and the number
of arguments is not checked.
.Ss \&de
Define a
.Nm
macro.
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.
.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.
Do not rely on the exact value of this limit.
.Ss \&dei
Define a
.Nm
macro, specifying the macro name indirectly.
The syntax of this request is the same as that of
.Sx \&de .
It is currently ignored by
.Xr mandoc 1 ,
as are its children.
.Ss \&de1
Define a
.Nm
macro that will be executed with
.Nm
compatibility mode switched off during macro execution.
This is a GNU extension not available in traditional
.Nm
implementations and not even in older versions of groff.
Since
.Xr mandoc 1
does not implement
.Nm
compatibility mode at all, it handles this request as an alias for
.Sx \&de .
.Ss \&ds
Define a user-defined string.
Its syntax is as follows:
.Pp
.D1 Pf . Cm \&ds Ar name Oo \(dq Oc Ns Ar string
.Pp
The
.Ar name
and
.Ar string
arguments are space-separated.
If the
.Ar string
begins with a double-quote character, that character will not be part
of the string.
All remaining characters on the input line form the
.Ar string ,
including whitespace and double-quote characters, even trailing ones.
.Pp
The
.Ar string
can be interpolated into subsequent text by using
.No \e* Ns Bq Ar name
for a
.Ar name
of arbitrary length, or \e*(NN or \e*N if the length of
.Ar name
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 \&el
The
.Qq else
half of an if/else conditional.
Pops a result off the stack of conditional evaluations pushed by
.Sx \&ie
and uses it as its conditional.
If no stack entries are present (e.g., due to no prior
.Sx \&ie
calls)
then false is assumed.
The syntax of this request is similar to
.Sx \&if
except that the conditional is missing.
.Ss \&EN
End an equation block.
See
.Sx \&EQ .
.Ss \&EQ
Begin an equation block.
See
.Xr eqn 7
for a description of the equation language.
.Ss \&fam
Change the font family.
This line-scoped request is intended to have one argument specifying
the font family to be selected.
It is a groff extension, and currently, it is ignored including its
arguments, and the number of arguments is not checked.
.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 \&hw
Specify hyphenation points in words.
This line-scoped request is currently ignored.
.Ss \&hy
Set automatic hyphenation mode.
This line-scoped request is currently ignored.
.Ss \&ie
The
.Qq if
half of an if/else conditional.
The result of the conditional is pushed into a stack used by subsequent
invocations of
.Sx \&el ,
which may be separated by any intervening input (or not exist at all).
Its syntax is equivalent to
.Sx \&if .
.Ss \&if
Begins a conditional.
This request has the following syntax:
.Bd -literal -offset indent
\&.if COND BODY
.Ed
.Bd -literal -offset indent
\&.if COND \e{BODY
BODY...\e}
.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 r
.Pq register accessed ,
or
.Sq t
.Pq troff mode ,
COND evaluates to false.
.It
If COND starts with a digit, optionally prefixed by a minus sign,
it is evaluated as a numerical expression of the form
.Ar number operator number ,
where
.Ar operator
is one of
.Sq < ,
.Sq <= ,
.Sq = ,
.Sq >= ,
or
.Sq > .
.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
syntactically interpreted to preserve the integrity of the input
document.
Thus,
.Pp
.D1 \&.if t .ig
.Pp
will discard the
.Sq \&.ig ,
which may lead to interesting results, but
.Pp
.D1 \&.if t .if t \e{\e
.Pp
will continue to syntactically interpret to the block close of the final
conditional.
Sub-conditionals, in this case, obviously inherit the truth value of
the parent.
.Pp
If the BODY section is begun by an escaped brace
.Sq \e{ ,
scope continues until the end of the input line containing the
matching closing-brace escape sequence
.Sq \e} .
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
brace or not, then requests and macros
.Em must
begin with a control character.
It is generally more intuitive, in this case, to write
.Bd -literal -offset indent
\&.if COND \e{\e
\&.foo
bar
\&.\e}
.Ed
.Pp
than having the request or macro follow as
.Pp
.D1 \&.if COND \e{ .foo
.Pp
The scope of a conditional is always parsed, but only executed if the
conditional evaluates to true.
.Pp
Note that the
.Sq \e}
is converted into a zero-width escape sequence if not passed as a
standalone macro
.Sq \&.\e} .
For example,
.Pp
.D1 \&.Fl a \e} b
.Pp
will result in
.Sq \e}
being considered an argument of the
.Sq \&Fl
macro.
.Ss \&ig
Ignore input.
Its syntax can be either
.Bd -literal -offset indent
.Pf . Cm \&ig
.Ar ignored text
\&..
.Ed
.Pp
or
.Bd -literal -offset indent
.Pf . Cm \&ig Ar end
.Ar ignored text
.Pf . Ar end
.Ed
.Pp
In the first case, input is ignored until a
.Sq \&..
request is encountered on its own line.
In the second case, input is ignored until the specified
.Sq Pf . Ar end
macro is encountered.
Do not use the escape character
.Sq \e
anywhere in the definition of
.Ar end ;
it would cause very strange behaviour.
.Pp
When the
.Ar end
macro is a roff request or a roff macro, like in
.Pp
.D1 \&.ig if
.Pp
the subsequent invocation of
.Sx \&if
will first terminate the
.Ar ignored text ,
then be invoked as usual.
Otherwise, it only terminates the
.Ar ignored text ,
and arguments following it or the
.Sq \&..
request are discarded.
.Ss \&ll
Change the output line length.
Its syntax is as follows:
.Pp
.D1 Pf . Cm \&ll Op 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.
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 \&ne
Declare the need for the specified minimum vertical space
before the next trap or the bottom of the page.
This line-scoped request is currently ignored.
.Ss \&nh
Turn off automatic hyphenation mode.
This line-scoped request is currently ignored.
.Ss \&rm
Remove a request, macro or string.
This request is intended to have one argument,
the name of the request, macro or string to be undefined.
Currently, it is ignored including its arguments,
and the number of arguments is not checked.
.Ss \&nr
Define or change a register.
A register is an arbitrary string value that defines some sort of state,
which influences parsing and/or formatting.
Its syntax is as follows:
.Pp
.D1 Pf \. Cm \&nr Ar name Oo +|- Oc Ns Ar value
.Pp
The
.Ar value
may, at the moment, only be an integer.
If it is prefixed by a sign, the register will be
incremented or decremented instead of assigned to.
.Pp
The following register
.Ar name
is handled specially:
.Bl -tag -width Ds
.It Cm nS
If set to a positive integer value, certain
.Xr mdoc 7
macros will behave in the same way as in the
.Em SYNOPSIS
section.
If set to 0, these macros will behave in the same way as outside the
.Em SYNOPSIS
section, even when called within the
.Em SYNOPSIS
section itself.
Note that starting a new
.Xr mdoc 7
section with the
.Cm \&Sh
macro will reset this register.
.El
.Ss \&ns
Turn on no-space mode.
This line-scoped request is intended to take no arguments.
Currently, it is ignored including its arguments,
and the number of arguments is not checked.
.Ss \&ps
Change point size.
This line-scoped request is intended to take one numerical argument.
Currently, it is ignored including its arguments,
and the number of arguments is not checked.
.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 \&ta
Set tab stops.
This line-scoped request can take an arbitrary number of arguments.
Currently, it is ignored including its arguments.
.Ss \&tr
Output character translation.
Its syntax is as follows:
.Pp
.D1 Pf \. Cm \&tr Ar [ab]+
.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 \&T&
Re-start a table layout, retaining the options of the prior table
invocation.
See
.Sx \&TS .
.Ss \&TE
End a table context.
See
.Sx \&TS .
.Ss \&TS
Begin a table, which formats input in aligned rows and columns.
See
.Xr tbl 7
for a description of the tbl language.
.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-
Special character
.Dq mathematical minus sign .
.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
Test whether
.Ar string
is a numerical expession; ignored by
.Xr mandoc 1 .
.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
Interrupt text processing to insert requests or macros; ignored by
.Xr mandoc 1 .
.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
.Ar string ;
ignored by
.Xr mandoc 1 .
.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 ;
ignored by
.Xr mandoc 1 .
.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;
approximated in
.Xr mandoc 1
by simply skipping the next character.
.Sh COMPATIBILITY
This section documents compatibility between mandoc and other
.Nm
implementations, at this time limited to GNU troff
.Pq Qq groff .
The term
.Qq historic groff
refers to groff version 1.15.
.Pp
.Bl -dash -compact
.It
In mandoc, the
.Sx \&EQ ,
.Sx \&TE ,
.Sx \&TS ,
and
.Sx \&T& ,
macros are considered regular macros.
In all other
.Nm
implementations, these are special macros that must be specified without
spacing between the control character (which must be a period) and the
macro name.
.It
The
.Cm nS
register is only compatible with OpenBSD's groff-1.15.
.It
Historic groff did not accept white-space before a custom
.Ar end
macro for the
.Sx \&ig
request.
.It
The
.Sx \&if
and family would print funny white-spaces with historic groff when
using the next-line syntax.
.El
.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
.An -nosplit
This
.Nm
reference was written by
.An Kristaps Dzonsons Aq Mt kristaps@bsd.lv
and
.An Ingo Schwarze Aq Mt schwarze@openbsd.org .
