contrib/mdocml/roff.7

.\"	$Id: roff.7,v 1.27 2011/02/09 10:03:02 kristaps Exp $
.\"
.\" Copyright (c) 2010 Kristaps Dzonsons <kristaps@bsd.lv>
.\" Copyright (c) 2010 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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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: February 9 2011 $
.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.
In particular, it serves as the basis for the
.Xr mdoc 7
and
.Xr man 7
manual formatting macro languages.
This manual describes the subset of the
.Nm
language accepted by the
.Xr mandoc 1
utility.
.Pp
Input lines beginning with the control characters
.Sq \&.
or
.Sq \(aq
are parsed for requests and macros.
These define the document structure, change the processing state
and manipulate the formatting.
Some requests and macros also produce formatted output,
while others do not.
.Pp
All other input lines provide free-form text to be printed;
the formatting of free-form 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.
To produce other characters in the output, use the escape sequences
documented in the
.Xr mandoc_char 7
manual.
.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 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 .
To be recognized as the beginning of a quoted argument, the opening
quote character must be preceded by a space character.
.Pp
A quoted argument may contain whitespace, and pairs of double quote
characters
.Pq Sq Qq
resolve to single double quote characters.
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.
.Sh REQUEST REFERENCE
The
.Xr mandoc 1
.Nm
parser recognizes 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 center 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 \&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 \&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.
Right now, the conditional evaluates to true
if and only if it starts with the letter
.Sy n ,
indicating processing in nroff style as opposed to troff style.
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.
This request has the following syntax:
.Bd -literal -offset indent
\&.if COND \e{\e
BODY...
\&.\e}
.Ed
.Bd -literal -offset indent
\&.if COND \e{ BODY
BODY... \e}
.Ed
.Bd -literal -offset indent
\&.if COND \e{ BODY
BODY...
\&.\e}
.Ed
.Bd -literal -offset indent
\&.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
.Sq \e{ ,
scope continues until a 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 text following an
.Sq \&.\e}
escape sequence is discarded.
Furthermore, if an explicit closing sequence
.Sq \e}
is specified in a free-form line, the entire line is accepted within the
scope of the prior request, not only the text preceding the close, with the
.Sq \e}
collapsing into a zero-width space.
.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 \&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 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 Ar value
.Pp
The
.Ar value
may, at the moment, only be an integer.
So far, only the following register
.Ar name
is recognised:
.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 inadvertant inclusion of unrelated files,
.Xr mandoc 1
only accepts relative paths not containing the strings
.Qq ../
and
.Qq /.. .
.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.
This request is intended to have one argument,
consisting of an even number of characters.
Currently, it is ignored including its arguments,
and the number of arguments is not checked.
.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 COMPATIBILITY
This section documents compatibility between mandoc and other 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 was written in PL/1 for the CTSS
operating system by Jerome ("Jerry") E. Saltzer in 1961.
It was first used as the main documentation tool by Multics since 1963.
Robert ("Bob") H. Morris ported it to the GE-635 and called it
.Nm ,
Doug McIlroy rewrote it in BCPL in 1969,
Joseph F. Ossanna rewrote it in PDP-11 assembly in 1973,
and Brian W. Kernighan rewrote it in C in 1975.
.Sh AUTHORS
.An -nosplit
This partial
.Nm
reference was written by
.An Kristaps Dzonsons Aq kristaps@bsd.lv
and
.An Ingo Schwarze Aq schwarze@openbsd.org .