Split tagging into a validation part including prioritization

in tag.{h,c} and {mdoc,man}_validate.c
and into a formatting part including command line argument checking
in term_tag.{h,c}, html.c, and {mdoc|man}_{term|html}.c.

Immediate functional benefits include:
* Improved prioritization of automatic tags for .Em and .Sy.
* Avoiding bogus automatic tags when .Em, .Fn, or .Sy are explicitly tagged.
* Explicit tagging of .Er and .Fl now works in HTML output.
* Automatic tagging of .IP and .TP now works in HTML output.
But mainly, this patch provides clean earth to build further improvements on.

Technical changes:
* Main program: Write a tag file for ASCII and UTF-8 output only.
* All formatters: There is no more need to delay writing the tags.
* mdoc(7)+man(7) formatters: No more need for elaborate syntax tree inspection.
* HTML formatter: If available, use the "string" attribute as the tag.
* HTML formatter: New function to write permalinks, to reduce code duplication.

Style cleanup in the vicinity while here:
* mdoc(7) terminal formatter: To set up bold font for children,
defer to termp_bold_pre() rather than calling term_fontpush() manually.
* mdoc(7) terminal formatter: Garbage collect some duplicate functions.
* mdoc(7) HTML formatter: Unify <code> handling, delete redundant functions.
* Where possible, use switch statements rather than if cascades.
* Get rid of some more Yoda notation.

The necessity for such changes was first discussed with kn@, but i didn't
bother him with a request to review the resulting -673/+782 line patch.

1 files changed, 7 insertions, 2 deletions

diff --git a/html.h b/html.h
index 69a75f2f..eb0c1bb1 100644
--- a/html.h
+++ b/html.h
@@ -1,7 +1,7 @@
-/*	$Id$ */
+/* $Id$ */
 /*
+ * Copyright (c) 2017, 2018, 2019, 2020 Ingo Schwarze <schwarze@openbsd.org>
  * Copyright (c) 2008-2011, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
- * Copyright (c) 2017, 2018, 2019 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
@@ -14,6 +14,9 @@
  * 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.
+ *
+ * Internal interfaces for mandoc(1) HTML formatters.
+ * For use by the individual HTML formatters only.
  */
 
 enum	htmltag {
@@ -120,6 +123,8 @@ void		  print_gen_comment(struct html *, struct roff_node *);
 void		  print_gen_decls(struct html *);
 void		  print_gen_head(struct html *);
 struct tag	 *print_otag(struct html *, enum htmltag, const char *, ...);
+struct tag	 *print_otag_id(struct html *, enum htmltag, const char *,
+			struct roff_node *);
 void		  print_tagq(struct html *, const struct tag *);
 void		  print_stagq(struct html *, const struct tag *);
 void		  print_text(struct html *, const char *);