.\"	$Id: eqn.7,v 1.3 2011/07/17 14:08:49 kristaps Exp $
.\"
.\" Copyright (c) 2011 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: July 17 2011 $
.Dt EQN 7
.Os
.Sh NAME
.Nm eqn
.Nd eqn language reference for mandoc
.Sh DESCRIPTION
The
.Nm eqn
language is a equation-formatting language.
It is used within
.Xr mdoc 7
and
.Xr man 7
.Ux
manual pages.
This manual describes the subset of the
.Nm
language accepted by the
.Xr mandoc 1
utility.
.Pp
Equations within
.Xr mdoc 7
or
.Xr man 7
documents are enclosed by the standalone
.Sq \&.EQ
and
.Sq \&.EN
tags.
Equations are multi-line blocks consisting of formulas and control
statements.
.Sh EQUATION STRUCTURE
Each equation is bracketed by
.Sq \&.EQ
and
.Sq \&.EN
strings.
.Em Note :
these are not the same as
.Xr roff 7
macros, and may only be invoked as
.Sq \&.EQ .
.Pp
The equation grammar is as follows:
.Bd -literal -offset indent
eqn     : box | eqn box
box     : text
        | DEFINE text text
        | SET text text
        | UNDEF text
text    : TEXT
.Ed
.Pp
Data in TEXT form is a non-empty sequence of non-space characters or a
non-empty quoted string.
White-space (and enclosing literal quote pairs) is thrown away and
productions may not be broken by newlines.
.Pp
The following control statements are available:
.Bl -tag -width Ds
.It Cm define
Replace all occurances of a key with a value.
Its syntax is as follows:
.Pp
.D1 define Ar key val
.Pp
It is an error to have an empty
.Ar key or
.Ar value .
Note that a quoted
.Ar key
causes errors in some
.Nm
implementations and should not be considered portable.
.It Cm set
Set an equation mode.  
Both arguments are thrown away.
.It Cm undef
Unset a previously-defined key.
Its syntax is as follows:
.Pp
.D1 define Ar key
.Pp
Once invoked, the definition for
.Ar key
is discarded.
.El
.Sh SEE ALSO
.Xr mandoc 1 ,
.Xr man 7 ,
.Xr mandoc_char 7 ,
.Xr mdoc 7 ,
.Xr roff 7
.Rs
.%A Brian W. Kernighan
.%A Lorinda L. Cherry
.%T System for Typesetting Mathematics
.%J Communications of the ACM
.%V 18
.%P 151\(en157
.%D March, 1975
.Re
.\" .Sh HISTORY
.\" The tbl utility, a preprocessor for troff, was originally written by M.
.\" E. Lesk at Bell Labs in 1975.
.\" The GNU reimplementation of tbl, part of the groff package, was released
.\" in 1990 by James Clark.
.\" A standalone tbl implementation was written by Kristaps Dzonsons in
.\" 2010.
.\" This formed the basis of the implementation that is part of the
.\" .Xr mandoc 1
.\" utility.
.Sh AUTHORS
This partial
.Nm
reference was written by
.An Kristaps Dzonsons Aq kristaps@bsd.lv .