mdocml: Add more documentation for libmandoc.

mdocml: Add more documentation for libmandoc.

[kristaps]

Log Message:
-----------
Add more documentation for libmandoc.

Modified Files:
--------------
    mdocml:
        mandoc.3

Revision Data
-------------
Index: mandoc.3
===================================================================
RCS file: /usr/vhosts/mdocml.bsd.lv/cvs/mdocml/mandoc.3,v
retrieving revision 1.10
retrieving revision 1.11
diff -Lmandoc.3 -Lmandoc.3 -u -p -r1.10 -r1.11
--- mandoc.3
+++ mandoc.3
@@ -177,9 +177,6 @@ library also contains routines for trans
 .Pq see Fn mchars_alloc
 and parsing escape sequences from strings
 .Pq see Fn mandoc_escape .
-.Pp
-This library is
-.Ud
 .Sh REFERENCE
 This section documents the functions, types, and variables available
 via
@@ -187,16 +184,35 @@ via
 .Ss Types
 .Bl -ohang
 .It Vt "enum mandoc_esc"
+An escape sequence classification.
 .It Vt "enum mandocerr"
+A fatal error, error, or warning message during parsing.
 .It Vt "enum mandoclevel"
+A classification of an
+.Vt "enum mandoclevel"
+as regards system operation.
 .It Vt "struct mchars"
 An opaque pointer to an object allowing for translation between
 character strings and glyphs.
 See
 .Fn mchars_alloc .
 .It Vt "enum mparset"
+The type of parser when reading input.
+This should usually be
+.Va MPARSE_AUTO
+for auto-detection.
 .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.
 .It Vt "mandocmsg"
+A prototype for a function to handle fatal error, error, and warning
+messages emitted by the parser.
 .El
 .Ss Functions
 .Bl -ohang
@@ -320,7 +336,36 @@ This section consists of structural docu
 .Xr mdoc 7
 and
 .Xr man 7
-syntax trees.
+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.
+.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
+.Fn mandoc_escape
+and converted with one of
+.Fn mchars_num2char ,
+.Fn mchars_spec2str ,
+and so on.
 .Ss Man Abstract Syntax Tree
 This AST is governed by the ontological rules dictated in
 .Xr man 7
@@ -361,7 +406,7 @@ where capitalised non-terminals represen
 .It ELEMENT
 \(<- ELEMENT | TEXT*
 .It TEXT
-\(<- [[:alpha:]]*
+\(<- [[:ascii:]]*
 .El
 .Pp
 The only elements capable of nesting other elements are those with
@@ -420,7 +465,7 @@ where capitalised non-terminals represen
 .It TAIL
 \(<- mnode*
 .It TEXT
-\(<- [[:printable:],0x1e]*
+\(<- [[:ascii:]]*
 .El
 .Pp
 Of note are the TEXT nodes following the HEAD, BODY and TAIL nodes of
--
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