contrib/mandoc/mandoc.3

.\" $Id: mandoc.3,v 1.46 2025/02/25 17:03:54 schwarze Exp $
.\"
.\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
.\" Copyright (c) 2010-2017 Ingo Schwarze <schwarze@openbsd.org>
.\"
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.\" 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.
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.Dd $Mdocdate: February 25 2025 $
.Dt MANDOC 3
.Os
.Sh NAME
.Nm mandoc ,
.Nm deroff ,
.Nm mparse_alloc ,
.Nm mparse_copy ,
.Nm mparse_free ,
.Nm mparse_open ,
.Nm mparse_readfd ,
.Nm mparse_reset ,
.Nm mparse_result
.Nd mandoc macro compiler library
.Sh SYNOPSIS
.In sys/types.h
.In stdio.h
.In mandoc.h
.In roff.h
.In mandoc_parse.h
.Pp
.Fd "#define ASCII_NBRSP"
.Fd "#define ASCII_HYPH"
.Fd "#define ASCII_BREAK"
.Ft struct mparse *
.Fo mparse_alloc
.Fa "int options"
.Fa "enum mandoc_os oe_e"
.Fa "char *os_s"
.Fc
.Ft void
.Fo mparse_free
.Fa "struct mparse *parse"
.Fc
.Ft void
.Fo mparse_copy
.Fa "const struct mparse *parse"
.Fc
.Ft int
.Fo mparse_open
.Fa "struct mparse *parse"
.Fa "const char *fname"
.Fc
.Ft void
.Fo mparse_readfd
.Fa "struct mparse *parse"
.Fa "int fd"
.Fa "const char *fname"
.Fc
.Ft void
.Fo mparse_reset
.Fa "struct mparse *parse"
.Fc
.Ft struct roff_meta *
.Fo mparse_result
.Fa "struct mparse *parse"
.Fc
.In roff.h
.Ft void
.Fo deroff
.Fa "char **dest"
.Fa "const struct roff_node *node"
.Fc
.In sys/types.h
.In mandoc.h
.In mdoc.h
.Vt extern const char * const * mdoc_argnames;
.Vt extern const char * const * mdoc_macronames;
.In sys/types.h
.In mandoc.h
.In man.h
.Vt extern const char * const * man_macronames;
.Sh DESCRIPTION
The
.Nm mandoc
library parses a
.Ux
manual into an abstract syntax tree (AST).
.Ux
manuals are composed of
.Xr mdoc 7
or
.Xr man 7 ,
and may be mixed with
.Xr roff 7 ,
.Xr tbl 7 ,
and
.Xr eqn 7
invocations.
.Pp
The following describes a general parse sequence:
.Bl -enum
.It
initiate a parsing sequence with
.Xr mchars_alloc 3
and
.Fn mparse_alloc ;
.It
open a file with
.Xr open 2
or
.Fn mparse_open ;
.It
parse it with
.Fn mparse_readfd ;
.It
close it with
.Xr close 2 ;
.It
retrieve the syntax tree with
.Fn mparse_result ;
.It
if information about the validity of the input is needed, fetch it with
.Fn mparse_updaterc ;
.It
iterate over parse nodes with starting from the
.Fa first
member of the returned
.Vt struct roff_meta ;
.It
free all allocated memory with
.Fn mparse_free
and
.Xr mchars_free 3 ,
or invoke
.Fn mparse_reset
and go back to step 2 to parse new files.
.El
.Pp
The design goals of the
.Nm mandoc
library are limited to providing the functionality required by the
.Xr mandoc 1
program.
Consequently, the functions documented in the present manual page
do not aim for API stability.
Any third-party program using them typically requires adjustments after every
.Nm mandoc
release.
Linking such a program requires
.Fl lz
because
.Fn mparse_readfd
calls
.Xr gzdopen 3 ,
.Xr gzread 3 ,
.Xr gzerror 3 ,
and
.Xr gzclose 3 .
For
.Xr mandoc 1
itself, the
.Pa ./configure
script automatically adds
.Fl lz
to the
.Ev LDADD
.Xr make 1
variable.
.Sh REFERENCE
This section documents the functions, types, and variables available
via
.In mandoc.h ,
with the exception of those documented in
.Xr mandoc_escape 3
and
.Xr mchars_alloc 3 .
.Ss Types
.Bl -ohang
.It Vt "enum mandocerr"
An error or warning message during parsing.
.It Vt "enum mandoclevel"
A classification of an
.Vt "enum mandocerr"
as regards system operation.
See the DIAGNOSTICS section in
.Xr mandoc 1
regarding the meanings of the levels.
.It Vt "struct mparse"
An opaque pointer to a running parse sequence.
Created with
.Fn mparse_alloc
and freed with
.Fn mparse_free .
This may be used across parsed input if
.Fn mparse_reset
is called between parses.
.El
.Ss Functions
.Bl -ohang
.It Fn deroff
Obtain a text-only representation of a
.Vt struct roff_node ,
including text contained in its child nodes.
To be used on children of the
.Fa first
member of
.Vt struct roff_meta .
When it is no longer needed, the pointer returned from
.Fn deroff
can be passed to
.Xr free 3 .
.It Fn mparse_alloc
Allocate a parser.
The arguments have the following effect:
.Bl -tag -offset 5n -width inttype
.It Ar options
When the
.Dv MPARSE_MDOC
or
.Dv MPARSE_MAN
bit is set, only that parser is used.
Otherwise, the document type is automatically detected.
.Pp
When the
.Dv MPARSE_SO
bit is set,
.Xr roff 7
.Ic \&so
file inclusion requests are always honoured.
Otherwise, if the request is the only content in an input file,
only the file name is remembered, to be returned in the
.Fa sodest
field of
.Vt struct roff_meta .
.Pp
When the
.Dv MPARSE_QUICK
bit is set, parsing is aborted after the NAME section.
This is for example useful in
.Xr makewhatis 8
.Fl Q
to quickly build minimal databases.
.Pp
When the
.Dv MARSE_VALIDATE
bit is set,
.Fn mparse_result
runs the validation functions before returning the syntax tree.
This is almost always required, except in certain debugging scenarios,
for example to dump unvalidated syntax trees.
.It Ar os_e
Operating system to check base system conventions for.
If
.Dv MANDOC_OS_OTHER ,
the system is automatically detected from
.Ic \&Os ,
.Fl Ios ,
or
.Xr uname 3 .
.It Ar os_s
A default string for the
.Xr mdoc 7
.Ic \&Os
macro, overriding the
.Dv OSNAME
preprocessor definition and the results of
.Xr uname 3 .
Passing
.Dv NULL
sets no default.
.El
.Pp
The same parser may be used for multiple files so long as
.Fn mparse_reset
is called between parses.
.Fn mparse_free
must be called to free the memory allocated by this function.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_free
Free all memory allocated by
.Fn mparse_alloc .
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_copy
Dump a copy of the input to the standard output; used for
.Fl man T Ns Cm man .
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_open
Open the file for reading.
If that fails and
.Fa fname
does not already end in
.Ql .gz ,
try again after appending
.Ql .gz .
Save the information whether the file is zipped or not.
Return a file descriptor open for reading or -1 on failure.
It can be passed to
.Fn mparse_readfd
or used directly.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_readfd
Parse a file descriptor opened with
.Xr open 2
or
.Fn mparse_open .
Pass the associated filename in
.Va fname .
This function may be called multiple times with different parameters; however,
.Xr close 2
and
.Fn mparse_reset
should be invoked between parses.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_reset
Reset a parser so that
.Fn mparse_readfd
may be used again.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.It Fn mparse_result
Obtain the result of a parse.
Declared in
.In mandoc.h ,
implemented in
.Pa read.c .
.El
.Ss Variables
.Bl -ohang
.It Va man_macronames
The string representation of a
.Xr man 7
macro as indexed by
.Vt "enum mant" .
.It Va mdoc_argnames
The string representation of an
.Xr mdoc 7
macro argument as indexed by
.Vt "enum mdocargt" .
.It Va mdoc_macronames
The string representation of an
.Xr mdoc 7
macro as indexed by
.Vt "enum mdoct" .
.El
.Sh IMPLEMENTATION NOTES
This section consists of structural documentation for
.Xr mdoc 7
and
.Xr man 7
syntax trees and strings.
.Ss Man and Mdoc Strings
Strings may be extracted from mdoc and man meta-data, or from text
nodes (MDOC_TEXT and MAN_TEXT, respectively).
These strings have special non-printing formatting cues embedded in the
text itself, as well as
.Xr roff 7
escapes preserved from input.
Implementing systems will need to handle both situations to produce
human-readable text.
In general, strings may be assumed to consist of 7-bit ASCII characters.
.Pp
The following non-printing characters may be embedded in text strings:
.Bl -tag -width Ds
.It Dv ASCII_NBRSP
A non-breaking space character.
.It Dv ASCII_HYPH
A soft hyphen.
.It Dv ASCII_BREAK
A breakable zero-width space.
.El
.Pp
Escape characters are also passed verbatim into text strings.
An escape character is a sequence of characters beginning with the
backslash
.Pq Sq \e .
To construct human-readable text, these should be intercepted with
.Xr mandoc_escape 3
and converted with one the functions described in
.Xr mchars_alloc 3 .
.Ss Man Abstract Syntax Tree
This AST is governed by the ontological rules dictated in
.Xr man 7
and derives its terminology accordingly.
.Pp
The AST is composed of
.Vt struct roff_node
nodes with element, root and text types as declared by the
.Va type
field.
Each node also provides its parse point (the
.Va line ,
.Va pos ,
and
.Va sec
fields), its position in the tree (the
.Va parent ,
.Va child ,
.Va next
and
.Va prev
fields) and some type-specific data.
.Pp
The tree itself is arranged according to the following normal form,
where capitalised non-terminals represent nodes.
.Pp
.Bl -tag -width "ELEMENTXX" -compact
.It ROOT
\(<- mnode+
.It mnode
\(<- ELEMENT | TEXT | BLOCK
.It BLOCK
\(<- HEAD BODY
.It HEAD
\(<- mnode*
.It BODY
\(<- mnode*
.It ELEMENT
\(<- ELEMENT | TEXT*
.It TEXT
\(<- [[:ascii:]]*
.El
.Pp
The only elements capable of nesting other elements are those with
next-line scope as documented in
.Xr man 7 .
.Ss Mdoc Abstract Syntax Tree
This AST is governed by the ontological
rules dictated in
.Xr mdoc 7
and derives its terminology accordingly.
.Qq In-line
elements described in
.Xr mdoc 7
are described simply as
.Qq elements .
.Pp
The AST is composed of
.Vt struct roff_node
nodes with block, head, body, element, root and text types as declared
by the
.Va type
field.
Each node also provides its parse point (the
.Va line ,
.Va pos ,
and
.Va sec
fields), its position in the tree (the
.Va parent ,
.Va child ,
.Va last ,
.Va next
and
.Va prev
fields) and some type-specific data, in particular, for nodes generated
from macros, the generating macro in the
.Va tok
field.
.Pp
The tree itself is arranged according to the following normal form,
where capitalised non-terminals represent nodes.
.Pp
.Bl -tag -width "ELEMENTXX" -compact
.It ROOT
\(<- mnode+
.It mnode
\(<- BLOCK | ELEMENT | TEXT
.It BLOCK
\(<- HEAD [TEXT] (BODY [TEXT])+ [TAIL [TEXT]]
.It ELEMENT
\(<- TEXT*
.It HEAD
\(<- mnode*
.It BODY
\(<- mnode* [ENDBODY mnode*]
.It TAIL
\(<- mnode*
.It TEXT
\(<- [[:ascii:]]*
.El
.Pp
Of note are the TEXT nodes following the HEAD, BODY and TAIL nodes of
the BLOCK production: these refer to punctuation marks.
Furthermore, although a TEXT node will generally have a non-zero-length
string, in the specific case of
.Sq \&.Bd \-literal ,
an empty line will produce a zero-length string.
Multiple body parts are only found in invocations of
.Sq \&Bl \-column ,
where a new body introduces a new phrase.
.Pp
The
.Xr mdoc 7
syntax tree accommodates for broken block structures as well.
The ENDBODY node is available to end the formatting associated
with a given block before the physical end of that block.
It has a non-null
.Va end
field, is of the BODY
.Va type ,
has the same
.Va tok
as the BLOCK it is ending, and has a
.Va pending
field pointing to that BLOCK's BODY node.
It is an indirect child of that BODY node
and has no children of its own.
.Pp
An ENDBODY node is generated when a block ends while one of its child
blocks is still open, like in the following example:
.Bd -literal -offset indent
\&.Ao ao
\&.Bo bo ac
\&.Ac bc
\&.Bc end
.Ed
.Pp
This example results in the following block structure:
.Bd -literal -offset indent
BLOCK Ao
    HEAD Ao
    BODY Ao
        TEXT ao
        BLOCK Bo, pending -> Ao
            HEAD Bo
            BODY Bo
                TEXT bo
                TEXT ac
                ENDBODY Ao, pending -> Ao
                TEXT bc
TEXT end
.Ed
.Pp
Here, the formatting of the
.Ic \&Ao
block extends from TEXT ao to TEXT ac,
while the formatting of the
.Ic \&Bo
block extends from TEXT bo to TEXT bc.
It renders as follows in
.Fl T Ns Cm ascii
mode:
.Pp
.Dl <ao [bo ac> bc] end
.Pp
Support for badly-nested blocks is only provided for backward
compatibility with some older
.Xr mdoc 7
implementations.
Using badly-nested blocks is
.Em strongly discouraged ;
for example, the
.Fl T Ns Cm html
front-end to
.Xr mandoc 1
is unable to render them in any meaningful way.
Furthermore, behaviour when encountering badly-nested blocks is not
consistent across troff implementations, especially when using multiple
levels of badly-nested blocks.
.Sh SEE ALSO
.Xr mandoc 1 ,
.Xr man.cgi 3 ,
.Xr mandoc_escape 3 ,
.Xr mandoc_headers 3 ,
.Xr mandoc_malloc 3 ,
.Xr mansearch 3 ,
.Xr mchars_alloc 3 ,
.Xr tbl 3 ,
.Xr eqn 7 ,
.Xr man 7 ,
.Xr mandoc_char 7 ,
.Xr mdoc 7 ,
.Xr roff 7 ,
.Xr tbl 7
.Sh AUTHORS
.An -nosplit
The
.Nm
library was written by
.An Kristaps Dzonsons Aq Mt kristaps@bsd.lv
and is maintained by
.An Ingo Schwarze Aq Mt schwarze@openbsd.org .