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.

16 files changed, 823 insertions, 788 deletions

diff --git a/usr.bin/mandoc/Makefile b/usr.bin/mandoc/Makefile
index 8c5a8f7d46b..8d6fec5e060 100644
--- a/usr.bin/mandoc/Makefile
+++ b/usr.bin/mandoc/Makefile
@@ -1,19 +1,19 @@
-#	$OpenBSD: Makefile,v 1.117 2019/03/06 12:26:30 schwarze Exp $
+# $OpenBSD: Makefile,v 1.118 2020/03/13 00:31:04 schwarze Exp $
 
 .include <bsd.own.mk>
 
 CFLAGS  += -W -Wall -Wstrict-prototypes -Wno-unused-parameter
-DPADD += ${LIBUTIL}
+DPADD	+= ${LIBUTIL}
 LDADD	+= -lutil -lz
 
 SRCS=	mandoc_aux.c mandoc_ohash.c mandoc.c mandoc_msg.c mandoc_xr.c \
-	arch.c chars.c preconv.c read.c \
-	roff.c roff_validate.c tbl.c tbl_opts.c tbl_layout.c tbl_data.c eqn.c
-SRCS+=	mdoc_macro.c mdoc.c \
-	mdoc_argv.c mdoc_state.c mdoc_validate.c att.c msec.c st.c
+	arch.c chars.c msec.c preconv.c read.c tag.c
+SRCS+=	roff.c roff_validate.c tbl.c tbl_opts.c tbl_layout.c tbl_data.c eqn.c
+SRCS+=	mdoc.c mdoc_argv.c mdoc_macro.c mdoc_state.c mdoc_validate.c \
+	att.c st.c
 SRCS+=	man_macro.c man.c man_validate.c
-SRCS+=	main.c out.c tag.c tree.c
-SRCS+=	term.c term_tab.c term_ascii.c term_ps.c
+SRCS+=	main.c out.c tree.c
+SRCS+=	term.c term_ascii.c term_ps.c term_tab.c term_tag.c
 SRCS+=	roff_term.c mdoc_term.c man_term.c eqn_term.c tbl_term.c
 SRCS+=	mdoc_man.c
 SRCS+=	html.c roff_html.c mdoc_html.c man_html.c eqn_html.c tbl_html.c
@@ -55,7 +55,7 @@ LIBROFF_OBJS =	roff.o roff_validate.o eqn.o \
 		tbl.o tbl_data.o tbl_layout.o tbl_opts.o
 LIBMANDOC_OBJS = ${LIBMDOC_OBJS} ${LIBMAN_OBJS} ${LIBROFF_OBJS} \
 		arch.o mandoc.o mandoc_aux.o mandoc_msg.o mandoc_ohash.o \
-		mandoc_xr.o chars.o msec.o preconv.o read.o
+		mandoc_xr.o chars.o msec.o preconv.o read.o tag.o
 HTML_OBJS =	html.o roff_html.o mdoc_html.o man_html.o \
 		tbl_html.o eqn_html.o out.o
 CGI_OBJS =	${LIBMANDOC_OBJS} ${HTML_OBJS} \
diff --git a/usr.bin/mandoc/html.c b/usr.bin/mandoc/html.c
index 102daabf3d9..c7c87c67a4e 100644
--- a/usr.bin/mandoc/html.c
+++ b/usr.bin/mandoc/html.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: html.c,v 1.134 2020/02/27 22:26:26 schwarze Exp $ */
+/* $OpenBSD: html.c,v 1.135 2020/03/13 00:31:04 schwarze Exp $ */
 /*
- * Copyright (c) 2008-2011, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2011-2015, 2017-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008-2011, 2014 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
@@ -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.
+ *
+ * Common functions for mandoc(1) HTML formatters.
+ * For use by individual formatters and by the main program.
  */
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -319,6 +322,18 @@ html_fillmode(struct html *h, enum roff_tok want)
 	return had;
 }
 
+/*
+ * Allocate a string to be used for the "id=" attribute of an HTML
+ * element and/or as a segment identifier for a URI in an <a> element.
+ * The function may fail and return NULL if the node lacks text data
+ * to create the attribute from.
+ * If the "unique" argument is 0, the caller is responsible for
+ * free(3)ing the returned string after using it.
+ * If the "unique" argument is non-zero, the "id_unique" ohash table
+ * is used for de-duplication and owns the returned string, so the
+ * caller must not free(3) it.  In this case, it will be freed
+ * automatically by html_reset() or html_free().
+ */
 char *
 html_make_id(const struct roff_node *n, int unique)
 {
@@ -327,14 +342,30 @@ html_make_id(const struct roff_node *n, int unique)
 	unsigned int		 slot;
 	int			 suffix;
 
-	for (nch = n->child; nch != NULL; nch = nch->next)
-		if (nch->type != ROFFT_TEXT)
-			return NULL;
-
-	buf = NULL;
-	deroff(&buf, n);
-	if (buf == NULL)
-		return NULL;
+	if (n->string != NULL)
+		buf = mandoc_strdup(n->string);
+	else {
+		switch (n->tok) {
+		case MDOC_Sh:
+		case MDOC_Ss:
+		case MDOC_Sx:
+		case MAN_SH:
+		case MAN_SS:
+			for (nch = n->child; nch != NULL; nch = nch->next)
+				if (nch->type != ROFFT_TEXT)
+					return NULL;
+			buf = NULL;
+			deroff(&buf, n);
+			if (buf == NULL)
+				return NULL;
+			break;
+		default:
+			if (n->child->type != ROFFT_TEXT)
+				return NULL;
+			buf = mandoc_strdup(n->child->string);
+			break;
+		}
+	}
 
 	/*
 	 * In ID attributes, only use ASCII characters that are
@@ -734,6 +765,33 @@ print_otag(struct html *h, enum htmltag tag, const char *fmt, ...)
 	return t;
 }
 
+/*
+ * Print an element with an optional "id=" attribute.
+ * If there is an "id=" attribute, also add a permalink:
+ * outside if it's a phrasing element, or inside otherwise.
+ */
+struct tag *
+print_otag_id(struct html *h, enum htmltag elemtype, const char *cattr,
+    struct roff_node *n)
+{
+	struct tag	*ret, *t;
+	const char	*id;
+
+	ret = NULL;
+	id = NULL;
+	if (n->flags & NODE_ID)
+		id = html_make_id(n, 1);
+	if (id != NULL && htmltags[elemtype].flags & HTML_INPHRASE)
+		ret = print_otag(h, TAG_A, "chR", "permalink", id);
+	t = print_otag(h, elemtype, "ci", cattr, id);
+	if (ret == NULL) {
+		ret = t;
+		if (id != NULL)
+			print_otag(h, TAG_A, "chR", "permalink", id);
+	}
+	return ret;
+}
+
 static void
 print_ctag(struct html *h, struct tag *tag)
 {
diff --git a/usr.bin/mandoc/html.h b/usr.bin/mandoc/html.h
index f0c9fe6d7a4..7bd55d48af5 100644
--- a/usr.bin/mandoc/html.h
+++ b/usr.bin/mandoc/html.h
@@ -1,7 +1,7 @@
-/*	$OpenBSD: html.h,v 1.68 2020/01/19 17:59:01 schwarze Exp $ */
+/* $OpenBSD: html.h,v 1.69 2020/03/13 00:31:04 schwarze Exp $ */
 /*
+ * 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 *);
diff --git a/usr.bin/mandoc/main.c b/usr.bin/mandoc/main.c
index 5c72f60ce7b..8931df51ea1 100644
--- a/usr.bin/mandoc/main.c
+++ b/usr.bin/mandoc/main.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: main.c,v 1.247 2020/02/24 21:15:05 schwarze Exp $ */
+/* $OpenBSD: main.c,v 1.248 2020/03/13 00:31:04 schwarze Exp $ */
 /*
- * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010-2012, 2014-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010 Joerg Sonnenberger <joerg@netbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
@@ -15,8 +15,9 @@
  * 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.
+ *
+ * Main program for mandoc(1), man(1), apropos(1), whatis(1), and help(1).
  */
-
 #include <sys/types.h>
 #include <sys/ioctl.h>
 #include <sys/param.h>	/* MACHINE */
@@ -46,7 +47,7 @@
 #include "mdoc.h"
 #include "man.h"
 #include "mandoc_parse.h"
-#include "tag.h"
+#include "term_tag.h"
 #include "main.h"
 #include "manconf.h"
 #include "mansearch.h"
@@ -577,7 +578,6 @@ main(int argc, char *argv[])
 	 * readable: Maybe it won't be needed after all.
 	 */
 	startdir = open(".", O_RDONLY | O_DIRECTORY);
-
 	for (i = 0; i < ressz; i++) {
 		process_onefile(mp, res + i, startdir, &outst, &conf);
 		if (outst.wstop && mandoc_msg_getrc() != MANDOCLEVEL_OK)
@@ -587,7 +587,6 @@ main(int argc, char *argv[])
 		(void)fchdir(startdir);
 		close(startdir);
 	}
-
 	if (outst.outdata != NULL) {
 		switch (outst.outtype) {
 		case OUTT_HTML:
@@ -596,6 +595,7 @@ main(int argc, char *argv[])
 		case OUTT_UTF8:
 		case OUTT_LOCALE:
 		case OUTT_ASCII:
+			term_tag_finish();
 			ascii_free(outst.outdata);
 			break;
 		case OUTT_PDF:
@@ -617,9 +617,8 @@ out:
 
 	if (outst.tag_files != NULL) {
 		fclose(stdout);
-		tag_write();
 		run_pager(outst.tag_files);
-		tag_unlink();
+		term_tag_unlink();
 	} else if (outst.had_output && outst.outtype != OUTT_LINT)
 		mandoc_msg_summary();
 
@@ -810,15 +809,16 @@ process_onefile(struct mparse *mp, struct manpage *resp, int startdir,
 	} else
 		fd = STDIN_FILENO;
 
-	if (outst->use_pager) {
-		outst->use_pager = 0;
-		outst->tag_files = tag_init(conf->output.tag);
-	}
-
-	if (outst->had_output && outst->outtype <= OUTT_UTF8) {
-		if (outst->outdata == NULL)
-			outdata_alloc(outst, &conf->output);
-		terminal_sepline(outst->outdata);
+	if (outst->outtype <= OUTT_UTF8) {
+		if (outst->use_pager) {
+			outst->use_pager = 0;
+			outst->tag_files = term_tag_init(conf->output.tag);
+		}
+		if (outst->had_output) {
+			if (outst->outdata == NULL)
+				outdata_alloc(outst, &conf->output);
+			terminal_sepline(outst->outdata);
+		}
 	}
 
 	if (resp->form == FORM_SRC)
@@ -832,7 +832,7 @@ process_onefile(struct mparse *mp, struct manpage *resp, int startdir,
 		if (outst->tag_files != NULL) {
 			mandoc_msg(MANDOCERR_WRITE, 0, 0, "%s: %s",
 			    outst->tag_files->ofn, strerror(errno));
-			tag_unlink();
+			term_tag_unlink();
 			outst->tag_files = NULL;
 		} else
 			mandoc_msg(MANDOCERR_WRITE, 0, 0, "%s",
@@ -1251,7 +1251,7 @@ spawn_pager(struct tag_files *tag_files)
 		_exit(mandoc_msg_getrc());
 	}
 	close(tag_files->ofd);
-	assert(tag_files->tfd == -1);
+	assert(tag_files->tfs == NULL);
 
 	/* Do not start the pager before controlling the terminal. */
 
diff --git a/usr.bin/mandoc/man_html.c b/usr.bin/mandoc/man_html.c
index 589b4114138..dd360649d6d 100644
--- a/usr.bin/mandoc/man_html.c
+++ b/usr.bin/mandoc/man_html.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: man_html.c,v 1.129 2020/02/27 01:25:57 schwarze Exp $ */
+/* $OpenBSD: man_html.c,v 1.130 2020/03/13 00:31:05 schwarze Exp $ */
 /*
- * Copyright (c) 2008-2012, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2013-2015, 2017-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008-2012, 2014 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
@@ -14,6 +14,8 @@
  * 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.
+ *
+ * HTML formatter for man(7) used by mandoc(1).
  */
 #include <sys/types.h>
 
@@ -308,7 +310,6 @@ static int
 man_SH_pre(MAN_ARGS)
 {
 	const char	*class;
-	char		*id;
 	enum htmltag	 tag;
 
 	if (n->tok == MAN_SH) {
@@ -324,10 +325,8 @@ man_SH_pre(MAN_ARGS)
 		print_otag(h, TAG_SECTION, "c", class);
 		break;
 	case ROFFT_HEAD:
-		id = html_make_id(n, 1);
-		print_otag(h, tag, "ci", class, id);
-		if (id != NULL)
-			print_otag(h, TAG_A, "chR", "permalink", id);
+		n->flags |= NODE_ID;
+		print_otag_id(h, tag, class, n);
 		break;
 	case ROFFT_BODY:
 		break;
@@ -487,7 +486,7 @@ man_IP_pre(MAN_ARGS)
 	case ROFFT_HEAD:
 		if (body_elem == TAG_LI)
 			return 0;
-		print_otag(h, TAG_DT, "");
+		print_otag_id(h, TAG_DT, NULL, n);
 		break;
 	case ROFFT_BODY:
 		print_otag(h, body_elem, "");
@@ -495,7 +494,6 @@ man_IP_pre(MAN_ARGS)
 	default:
 		abort();
 	}
-
 	switch(n->tok) {
 	case MAN_IP:  /* Only print the first header element. */
 		if (n->child != NULL)
diff --git a/usr.bin/mandoc/man_term.c b/usr.bin/mandoc/man_term.c
index 33ae377ffb9..3bf25adbf54 100644
--- a/usr.bin/mandoc/man_term.c
+++ b/usr.bin/mandoc/man_term.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: man_term.c,v 1.187 2020/02/27 01:25:57 schwarze Exp $ */
+/* $OpenBSD: man_term.c,v 1.188 2020/03/13 00:31:05 schwarze Exp $ */
 /*
- * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010-2015, 2017-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008-2012 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
@@ -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.
+ *
+ * Plain text formatter for man(7), used by mandoc(1)
+ * for ASCII, UTF-8, PostScript, and PDF output.
  */
 #include <sys/types.h>
 
@@ -30,7 +33,7 @@
 #include "man.h"
 #include "out.h"
 #include "term.h"
-#include "tag.h"
+#include "term_tag.h"
 #include "main.h"
 
 #define	MAXMARGINS	  64 /* maximum number of indented scopes */
@@ -92,8 +95,6 @@ static	void		  post_SY(DECL_ARGS);
 static	void		  post_TP(DECL_ARGS);
 static	void		  post_UR(DECL_ARGS);
 
-static	void		  tag_man(struct termp *, struct roff_node *);
-
 static const struct man_term_act man_term_acts[MAN_MAX - MAN_TH] = {
 	{ NULL, NULL, 0 }, /* TH */
 	{ pre_SH, post_SH, 0 }, /* SH */
@@ -537,10 +538,8 @@ pre_IP(DECL_ARGS)
 	case ROFFT_HEAD:
 		p->tcol->offset = mt->offset;
 		p->tcol->rmargin = mt->offset + len;
-		if (n->child != NULL) {
+		if (n->child != NULL)
 			print_man_node(p, mt, n->child, meta);
-			tag_man(p, n->child);
-		}
 		return 0;
 	case ROFFT_BODY:
 		p->tcol->offset = mt->offset + len;
@@ -620,18 +619,6 @@ pre_TP(DECL_ARGS)
 		while (nn != NULL && (nn->flags & NODE_LINE) == 0)
 			nn = nn->next;
 
-		if (nn == NULL)
-			return 0;
-
-		if (nn->type == ROFFT_TEXT)
-			tag_man(p, nn);
-		else if (nn->child != NULL &&
-		    nn->child->type == ROFFT_TEXT &&
-		    (nn->tok == MAN_B || nn->tok == MAN_BI ||
-		     nn->tok == MAN_BR || nn->tok == MAN_I ||
-		     nn->tok == MAN_IB || nn->tok == MAN_IR))
-			tag_man(p, nn->child);
-
 		while (nn != NULL) {
 			print_man_node(p, mt, nn, meta);
 			nn = nn->next;
@@ -911,6 +898,9 @@ print_man_node(DECL_ARGS)
 	const struct man_term_act *act;
 	int c;
 
+	if (n->flags & NODE_ID)
+		term_tag_write(n, p->line);
+
 	switch (n->type) {
 	case ROFFT_TEXT:
 		/*
@@ -1157,60 +1147,3 @@ print_man_head(struct termp *p, const struct roff_meta *meta)
 	}
 	free(title);
 }
-
-/*
- * Skip leading whitespace, dashes, backslashes, and font escapes,
- * then create a tag if the first following byte is a letter.
- * Priority is high unless whitespace is present.
- */
-static void
-tag_man(struct termp *p, struct roff_node *n)
-{
-	const char	*cp, *arg;
-	int		 prio, sz;
-
-	assert(n->type == ROFFT_TEXT);
-	cp = n->string;
-	prio = TAG_STRONG;
-	for (;;) {
-		switch (*cp) {
-		case ' ':
-		case '\t':
-			prio = TAG_WEAK;
-			/* FALLTHROUGH */
-		case '-':
-			cp++;
-			break;
-		case '\\':
-			cp++;
-			switch (mandoc_escape(&cp, &arg, &sz)) {
-			case ESCAPE_FONT:
-			case ESCAPE_FONTROMAN:
-			case ESCAPE_FONTITALIC:
-			case ESCAPE_FONTBOLD:
-			case ESCAPE_FONTPREV:
-			case ESCAPE_FONTBI:
-				break;
-			case ESCAPE_SPECIAL:
-				if (sz != 1)
-					return;
-				switch (*arg) {
-				case '&':
-				case '-':
-				case 'e':
-					break;
-				default:
-					return;
-				}
-				break;
-			default:
-				return;
-			}
-			break;
-		default:
-			if (isalpha((unsigned char)*cp))
-				tag_put(cp, prio, p->line);
-			return;
-		}
-	}
-}
diff --git a/usr.bin/mandoc/man_validate.c b/usr.bin/mandoc/man_validate.c
index 897fead07cf..4ab8c2cce11 100644
--- a/usr.bin/mandoc/man_validate.c
+++ b/usr.bin/mandoc/man_validate.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: man_validate.c,v 1.120 2020/01/19 16:16:32 schwarze Exp $ */
+/* $OpenBSD: man_validate.c,v 1.121 2020/03/13 00:31:05 schwarze Exp $ */
 /*
- * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010, 2012-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008, 2009, 2010, 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
@@ -14,6 +14,8 @@
  * 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.
+ *
+ * Validation module for man(7) syntax trees used by mandoc(1).
  */
 #include <sys/types.h>
 
@@ -30,6 +32,7 @@
 #include "mandoc_aux.h"
 #include "mandoc.h"
 #include "roff.h"
+#include "tag.h"
 #include "man.h"
 #include "libmandoc.h"
 #include "roff_int.h"
@@ -43,6 +46,7 @@ static	void	  check_abort(CHKARGS) __attribute__((__noreturn__));
 static	void	  check_par(CHKARGS);
 static	void	  check_part(CHKARGS);
 static	void	  check_root(CHKARGS);
+static	void	  check_tag(struct roff_node *, struct roff_node *);
 static	void	  check_text(CHKARGS);
 
 static	void	  post_AT(CHKARGS);
@@ -52,6 +56,7 @@ static	void	  post_IP(CHKARGS);
 static	void	  post_OP(CHKARGS);
 static	void	  post_SH(CHKARGS);
 static	void	  post_TH(CHKARGS);
+static	void	  post_TP(CHKARGS);
 static	void	  post_UC(CHKARGS);
 static	void	  post_UR(CHKARGS);
 static	void	  post_in(CHKARGS);
@@ -60,8 +65,8 @@ static	const v_check man_valids[MAN_MAX - MAN_TH] = {
 	post_TH,    /* TH */
 	post_SH,    /* SH */
 	post_SH,    /* SS */
-	NULL,       /* TP */
-	NULL,       /* TQ */
+	post_TP,    /* TP */
+	post_TP,    /* TQ */
 	check_abort,/* LP */
 	check_par,  /* PP */
 	check_abort,/* P */
@@ -199,6 +204,66 @@ check_abort(CHKARGS)
 	abort();
 }
 
+/*
+ * Skip leading whitespace, dashes, backslashes, and font escapes,
+ * then create a tag if the first following byte is a letter.
+ * Priority is high unless whitespace is present.
+ */
+static void
+check_tag(struct roff_node *n, struct roff_node *nt)
+{
+	const char	*cp, *arg;
+	int		 prio, sz;
+
+	if (nt == NULL || nt->type != ROFFT_TEXT)
+		return;
+
+	cp = nt->string;
+	prio = TAG_STRONG;
+	for (;;) {
+		switch (*cp) {
+		case ' ':
+		case '\t':
+			prio = TAG_WEAK;
+			/* FALLTHROUGH */
+		case '-':
+			cp++;
+			break;
+		case '\\':
+			cp++;
+			switch (mandoc_escape(&cp, &arg, &sz)) {
+			case ESCAPE_FONT:
+			case ESCAPE_FONTBOLD:
+			case ESCAPE_FONTITALIC:
+			case ESCAPE_FONTBI:
+			case ESCAPE_FONTROMAN:
+			case ESCAPE_FONTCW:
+			case ESCAPE_FONTPREV:
+			case ESCAPE_IGNORE:
+				break;
+			case ESCAPE_SPECIAL:
+				if (sz != 1)
+					return;
+				switch (*arg) {
+				case '-':
+				case 'e':
+					break;
+				default:
+					return;
+				}
+				break;
+			default:
+				return;
+			}
+			break;
+		default:
+			if (isalpha((unsigned char)*cp))
+				tag_put(cp, prio, n);
+			return;
+		}
+	}
+}
+
 static void
 check_text(CHKARGS)
 {
@@ -330,12 +395,14 @@ check_par(CHKARGS)
 static void
 post_IP(CHKARGS)
 {
-
 	switch (n->type) {
 	case ROFFT_BLOCK:
 		if (n->head->child == NULL && n->body->child == NULL)
 			roff_node_delete(man, n);
 		break;
+	case ROFFT_HEAD:
+		check_tag(n, n->child);
+		break;
 	case ROFFT_BODY:
 		if (n->parent->head->child == NULL && n->child == NULL)
 			mandoc_msg(MANDOCERR_PAR_SKIP, n->line, n->pos,
@@ -346,6 +413,37 @@ post_IP(CHKARGS)
 	}
 }
 
+/*
+ * The first next-line element in the head is the tag.
+ * If that's a font macro, use its first child instead.
+ */
+static void
+post_TP(CHKARGS)
+{
+	struct roff_node *nt;
+
+	if (n->type != ROFFT_HEAD || (nt = n->child) == NULL)
+		return;
+
+	while ((nt->flags & NODE_LINE) == 0)
+		if ((nt = nt->next) == NULL)
+			return;
+
+	switch (nt->tok) {
+	case MAN_B:
+	case MAN_BI:
+	case MAN_BR:
+	case MAN_I:
+	case MAN_IB:
+	case MAN_IR:
+		nt = nt->child;
+		break;
+	default:
+		break;
+	}
+	check_tag(n, nt);
+}
+
 static void
 post_TH(CHKARGS)
 {
diff --git a/usr.bin/mandoc/mdoc_html.c b/usr.bin/mandoc/mdoc_html.c
index 2dfc43a2123..e20126a9bd4 100644
--- a/usr.bin/mandoc/mdoc_html.c
+++ b/usr.bin/mandoc/mdoc_html.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: mdoc_html.c,v 1.210 2020/02/27 22:26:26 schwarze Exp $ */
+/* $OpenBSD: mdoc_html.c,v 1.211 2020/03/13 00:31:05 schwarze Exp $ */
 /*
- * Copyright (c) 2008-2011, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2014-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008-2011, 2014 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
@@ -14,6 +14,8 @@
  * 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.
+ *
+ * HTML formatter for mdoc(7) used by mandoc(1).
  */
 #include <sys/types.h>
 
@@ -45,7 +47,6 @@ struct	mdoc_html_act {
 	void		(*post)(MDOC_ARGS);
 };
 
-static	char		 *cond_id(const struct roff_node *);
 static	void		  print_mdoc_head(const struct roff_meta *,
 				struct html *);
 static	void		  print_mdoc_node(MDOC_ARGS);
@@ -70,9 +71,8 @@ static	void		  mdoc_bk_post(MDOC_ARGS);
 static	int		  mdoc_bk_pre(MDOC_ARGS);
 static	int		  mdoc_bl_pre(MDOC_ARGS);
 static	int		  mdoc_cd_pre(MDOC_ARGS);
-static	int		  mdoc_cm_pre(MDOC_ARGS);
+static	int		  mdoc_code_pre(MDOC_ARGS);
 static	int		  mdoc_d1_pre(MDOC_ARGS);
-static	int		  mdoc_dv_pre(MDOC_ARGS);
 static	int		  mdoc_fa_pre(MDOC_ARGS);
 static	int		  mdoc_fd_pre(MDOC_ARGS);
 static	int		  mdoc_fl_pre(MDOC_ARGS);
@@ -81,20 +81,15 @@ static	int		  mdoc_ft_pre(MDOC_ARGS);
 static	int		  mdoc_em_pre(MDOC_ARGS);
 static	void		  mdoc_eo_post(MDOC_ARGS);
 static	int		  mdoc_eo_pre(MDOC_ARGS);
-static	int		  mdoc_er_pre(MDOC_ARGS);
-static	int		  mdoc_ev_pre(MDOC_ARGS);
 static	int		  mdoc_ex_pre(MDOC_ARGS);
 static	void		  mdoc_fo_post(MDOC_ARGS);
 static	int		  mdoc_fo_pre(MDOC_ARGS);
-static	int		  mdoc_ic_pre(MDOC_ARGS);
 static	int		  mdoc_igndelim_pre(MDOC_ARGS);
 static	int		  mdoc_in_pre(MDOC_ARGS);
 static	int		  mdoc_it_pre(MDOC_ARGS);
 static	int		  mdoc_lb_pre(MDOC_ARGS);
-static	int		  mdoc_li_pre(MDOC_ARGS);
 static	int		  mdoc_lk_pre(MDOC_ARGS);
 static	int		  mdoc_mt_pre(MDOC_ARGS);
-static	int		  mdoc_ms_pre(MDOC_ARGS);
 static	int		  mdoc_nd_pre(MDOC_ARGS);
 static	int		  mdoc_nm_pre(MDOC_ARGS);
 static	int		  mdoc_no_pre(MDOC_ARGS);
@@ -137,19 +132,19 @@ static const struct mdoc_html_act mdoc_html_acts[MDOC_MAX - MDOC_Dd] = {
 	{mdoc_ap_pre, NULL}, /* Ap */
 	{mdoc_ar_pre, NULL}, /* Ar */
 	{mdoc_cd_pre, NULL}, /* Cd */
-	{mdoc_cm_pre, NULL}, /* Cm */
-	{mdoc_dv_pre, NULL}, /* Dv */
-	{mdoc_er_pre, NULL}, /* Er */
-	{mdoc_ev_pre, NULL}, /* Ev */
+	{mdoc_code_pre, NULL}, /* Cm */
+	{mdoc_code_pre, NULL}, /* Dv */
+	{mdoc_code_pre, NULL}, /* Er */
+	{mdoc_code_pre, NULL}, /* Ev */
 	{mdoc_ex_pre, NULL}, /* Ex */
 	{mdoc_fa_pre, NULL}, /* Fa */
 	{mdoc_fd_pre, NULL}, /* Fd */
 	{mdoc_fl_pre, NULL}, /* Fl */
 	{mdoc_fn_pre, NULL}, /* Fn */
 	{mdoc_ft_pre, NULL}, /* Ft */
-	{mdoc_ic_pre, NULL}, /* Ic */
+	{mdoc_code_pre, NULL}, /* Ic */
 	{mdoc_in_pre, NULL}, /* In */
-	{mdoc_li_pre, NULL}, /* Li */
+	{mdoc_code_pre, NULL}, /* Li */
 	{mdoc_nd_pre, NULL}, /* Nd */
 	{mdoc_nm_pre, NULL}, /* Nm */
 	{mdoc_quote_pre, mdoc_quote_post}, /* Op */
@@ -190,7 +185,7 @@ static const struct mdoc_html_act mdoc_html_acts[MDOC_MAX - MDOC_Dd] = {
 	{mdoc_em_pre, NULL}, /* Em */
 	{mdoc_eo_pre, mdoc_eo_post}, /* Eo */
 	{mdoc_xx_pre, NULL}, /* Fx */
-	{mdoc_ms_pre, NULL}, /* Ms */
+	{mdoc_no_pre, NULL}, /* Ms */
 	{mdoc_no_pre, NULL}, /* No */
 	{mdoc_ns_pre, NULL}, /* Ns */
 	{mdoc_xx_pre, NULL}, /* Nx */
@@ -505,20 +500,11 @@ mdoc_root_pre(const struct roff_meta *meta, struct html *h)
 	return 1;
 }
 
-static char *
-cond_id(const struct roff_node *n)
+static int
+mdoc_code_pre(MDOC_ARGS)
 {
-	if (n->child != NULL &&
-	    n->child->type == ROFFT_TEXT &&
-	    (n->prev == NULL ||
-	     (n->prev->type == ROFFT_TEXT &&
-	      strcmp(n->prev->string, "|") == 0)) &&
-	    (n->parent->tok == MDOC_It ||
-	     (n->parent->tok == MDOC_Xo &&
-	      n->parent->parent->prev == NULL &&
-	      n->parent->parent->parent->tok == MDOC_It)))
-		return html_make_id(n, 1);
-	return NULL;
+	print_otag_id(h, TAG_CODE, roff_name[n->tok], n);
+	return 1;
 }
 
 static int
@@ -581,10 +567,8 @@ mdoc_sh_pre(MDOC_ARGS)
 		print_otag(h, TAG_SECTION, "c", "Sh");
 		break;
 	case ROFFT_HEAD:
-		id = html_make_id(n, 1);
-		print_otag(h, TAG_H1, "ci", "Sh", id);
-		if (id != NULL)
-			print_otag(h, TAG_A, "chR", "permalink", id);
+		n->flags |= NODE_ID;
+		print_otag_id(h, TAG_H1, "Sh", n);
 		break;
 	case ROFFT_BODY:
 		if (n->sec == SEC_AUTHORS)
@@ -599,25 +583,20 @@ mdoc_sh_pre(MDOC_ARGS)
 static int
 mdoc_ss_pre(MDOC_ARGS)
 {
-	char	*id;
-
 	switch (n->type) {
 	case ROFFT_BLOCK:
 		html_close_paragraph(h);
 		print_otag(h, TAG_SECTION, "c", "Ss");
-		return 1;
+		break;
 	case ROFFT_HEAD:
+		n->flags |= NODE_ID;
+		print_otag_id(h, TAG_H2, "Ss", n);
 		break;
 	case ROFFT_BODY:
-		return 1;
+		break;
 	default:
 		abort();
 	}
-
-	id = html_make_id(n, 1);
-	print_otag(h, TAG_H2, "ci", "Ss", id);
-	if (id != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
 	return 1;
 }
 
@@ -625,12 +604,8 @@ static int
 mdoc_fl_pre(MDOC_ARGS)
 {
 	struct roff_node	*nn;
-	char			*id;
-
-	if ((id = cond_id(n)) != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_CODE, "ci", "Fl", id);
 
+	print_otag_id(h, TAG_CODE, "Fl", n);
 	print_text(h, "\\-");
 	if (n->child != NULL ||
 	    ((nn = roff_node_next(n)) != NULL &&
@@ -642,17 +617,6 @@ mdoc_fl_pre(MDOC_ARGS)
 }
 
 static int
-mdoc_cm_pre(MDOC_ARGS)
-{
-	char	*id;
-
-	if ((id = cond_id(n)) != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_CODE, "ci", "Cm", id);
-	return 1;
-}
-
-static int
 mdoc_nd_pre(MDOC_ARGS)
 {
 	switch (n->type) {
@@ -924,7 +888,7 @@ mdoc_st_pre(MDOC_ARGS)
 static int
 mdoc_em_pre(MDOC_ARGS)
 {
-	print_otag(h, TAG_I, "c", "Em");
+	print_otag_id(h, TAG_I, "Em", n);
 	return 1;
 }
 
@@ -1050,45 +1014,6 @@ mdoc_cd_pre(MDOC_ARGS)
 }
 
 static int
-mdoc_dv_pre(MDOC_ARGS)
-{
-	char	*id;
-
-	if ((id = cond_id(n)) != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_CODE, "ci", "Dv", id);
-	return 1;
-}
-
-static int
-mdoc_ev_pre(MDOC_ARGS)
-{
-	char	*id;
-
-	if ((id = cond_id(n)) != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_CODE, "ci", "Ev", id);
-	return 1;
-}
-
-static int
-mdoc_er_pre(MDOC_ARGS)
-{
-	char	*id;
-
-	id = n->sec == SEC_ERRORS &&
-	    (n->parent->tok == MDOC_It ||
-	     (n->parent->tok == MDOC_Bq &&
-	      n->parent->parent->parent->tok == MDOC_It)) ?
-	    html_make_id(n, 1) : NULL;
-
-	if (id != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_CODE, "ci", "Er", id);
-	return 1;
-}
-
-static int
 mdoc_fa_pre(MDOC_ARGS)
 {
 	const struct roff_node	*nn;
@@ -1220,7 +1145,7 @@ mdoc_fn_pre(MDOC_ARGS)
 		print_tagq(h, t);
 	}
 
-	t = print_otag(h, TAG_CODE, "c", "Fn");
+	t = print_otag_id(h, TAG_CODE, "Fn", n);
 
 	if (sp)
 		print_text(h, sp);
@@ -1339,14 +1264,12 @@ mdoc_mt_pre(MDOC_ARGS)
 
 	for (n = n->child; n; n = n->next) {
 		assert(n->type == ROFFT_TEXT);
-
 		mandoc_asprintf(&cp, "mailto:%s", n->string);
 		t = print_otag(h, TAG_A, "ch", "Mt", cp);
 		print_text(h, n->string);
 		print_tagq(h, t);
 		free(cp);
 	}
-
 	return 0;
 }
 
@@ -1355,30 +1278,30 @@ mdoc_fo_pre(MDOC_ARGS)
 {
 	struct tag	*t;
 
-	if (n->type == ROFFT_BODY) {
+	switch (n->type) {
+	case ROFFT_BLOCK:
+		synopsis_pre(h, n);
+		return 1;
+	case ROFFT_HEAD:
+		if (n->child != NULL) {
+			t = print_otag_id(h, TAG_CODE, "Fn", n);
+			print_text(h, n->child->string);
+			print_tagq(h, t);
+		}
+		return 0;
+	case ROFFT_BODY:
 		h->flags |= HTML_NOSPACE;
 		print_text(h, "(");
 		h->flags |= HTML_NOSPACE;
 		return 1;
-	} else if (n->type == ROFFT_BLOCK) {
-		synopsis_pre(h, n);
-		return 1;
+	default:
+		abort();
 	}
-
-	if (n->child == NULL)
-		return 0;
-
-	assert(n->child->string);
-	t = print_otag(h, TAG_CODE, "c", "Fn");
-	print_text(h, n->child->string);
-	print_tagq(h, t);
-	return 0;
 }
 
 static void
 mdoc_fo_post(MDOC_ARGS)
 {
-
 	if (n->type != ROFFT_BODY)
 		return;
 	h->flags |= HTML_NOSPACE;
@@ -1428,22 +1351,10 @@ mdoc_in_pre(MDOC_ARGS)
 		assert(n->type == ROFFT_TEXT);
 		print_text(h, n->string);
 	}
-
 	return 0;
 }
 
 static int
-mdoc_ic_pre(MDOC_ARGS)
-{
-	char	*id;
-
-	if ((id = cond_id(n)) != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_CODE, "ci", "Ic", id);
-	return 1;
-}
-
-static int
 mdoc_va_pre(MDOC_ARGS)
 {
 	print_otag(h, TAG_VAR, "c", "Va");
@@ -1453,7 +1364,6 @@ mdoc_va_pre(MDOC_ARGS)
 static int
 mdoc_ap_pre(MDOC_ARGS)
 {
-
 	h->flags |= HTML_NOSPACE;
 	print_text(h, "\\(aq");
 	h->flags |= HTML_NOSPACE;
@@ -1492,20 +1402,8 @@ mdoc_bf_pre(MDOC_ARGS)
 }
 
 static int
-mdoc_ms_pre(MDOC_ARGS)
-{
-	char *id;
-
-	if ((id = cond_id(n)) != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_SPAN, "ci", "Ms", id);
-	return 1;
-}
-
-static int
 mdoc_igndelim_pre(MDOC_ARGS)
 {
-
 	h->flags |= HTML_IGNDELIM;
 	return 1;
 }
@@ -1513,7 +1411,6 @@ mdoc_igndelim_pre(MDOC_ARGS)
 static void
 mdoc_pf_post(MDOC_ARGS)
 {
-
 	if ( ! (n->next == NULL || n->next->flags & NODE_LINE))
 		h->flags |= HTML_NOSPACE;
 }
@@ -1542,29 +1439,14 @@ mdoc_rs_pre(MDOC_ARGS)
 static int
 mdoc_no_pre(MDOC_ARGS)
 {
-	char *id;
-
-	if ((id = cond_id(n)) != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_SPAN, "ci", "No", id);
-	return 1;
-}
-
-static int
-mdoc_li_pre(MDOC_ARGS)
-{
-	char	*id;
-
-	if ((id = cond_id(n)) != NULL)
-		print_otag(h, TAG_A, "chR", "permalink", id);
-	print_otag(h, TAG_CODE, "ci", "Li", id);
+	print_otag_id(h, TAG_SPAN, roff_name[n->tok], n);
 	return 1;
 }
 
 static int
 mdoc_sy_pre(MDOC_ARGS)
 {
-	print_otag(h, TAG_B, "c", "Sy");
+	print_otag_id(h, TAG_B, "Sy", n);
 	return 1;
 }
 
diff --git a/usr.bin/mandoc/mdoc_term.c b/usr.bin/mandoc/mdoc_term.c
index 54252473702..edbbec08797 100644
--- a/usr.bin/mandoc/mdoc_term.c
+++ b/usr.bin/mandoc/mdoc_term.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: mdoc_term.c,v 1.277 2020/02/27 21:38:27 schwarze Exp $ */
+/* $OpenBSD: mdoc_term.c,v 1.278 2020/03/13 00:31:05 schwarze Exp $ */
 /*
- * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010, 2012-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2013 Franco Fichtner <franco@lastsummer.de>
  *
  * Permission to use, copy, modify, and distribute this software for any
@@ -15,6 +15,9 @@
  * 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.
+ *
+ * Plain text formatter for mdoc(7), used by mandoc(1)
+ * for ASCII, UTF-8, PostScript, and PDF output.
  */
 #include <sys/types.h>
 
@@ -31,7 +34,7 @@
 #include "mdoc.h"
 #include "out.h"
 #include "term.h"
-#include "tag.h"
+#include "term_tag.h"
 #include "main.h"
 
 struct	termpair {
@@ -87,11 +90,8 @@ static	int	  termp_bf_pre(DECL_ARGS);
 static	int	  termp_bk_pre(DECL_ARGS);
 static	int	  termp_bl_pre(DECL_ARGS);
 static	int	  termp_bold_pre(DECL_ARGS);
-static	int	  termp_cd_pre(DECL_ARGS);
 static	int	  termp_d1_pre(DECL_ARGS);
 static	int	  termp_eo_pre(DECL_ARGS);
-static	int	  termp_em_pre(DECL_ARGS);
-static	int	  termp_er_pre(DECL_ARGS);
 static	int	  termp_ex_pre(DECL_ARGS);
 static	int	  termp_fa_pre(DECL_ARGS);
 static	int	  termp_fd_pre(DECL_ARGS);
@@ -113,8 +113,6 @@ static	int	  termp_skip_pre(DECL_ARGS);
 static	int	  termp_sm_pre(DECL_ARGS);
 static	int	  termp_pp_pre(DECL_ARGS);
 static	int	  termp_ss_pre(DECL_ARGS);
-static	int	  termp_sy_pre(DECL_ARGS);
-static	int	  termp_tag_pre(DECL_ARGS);
 static	int	  termp_under_pre(DECL_ARGS);
 static	int	  termp_vt_pre(DECL_ARGS);
 static	int	  termp_xr_pre(DECL_ARGS);
@@ -138,11 +136,11 @@ static const struct mdoc_term_act mdoc_term_acts[MDOC_MAX - MDOC_Dd] = {
 	{ termp_an_pre, NULL }, /* An */
 	{ termp_ap_pre, NULL }, /* Ap */
 	{ termp_under_pre, NULL }, /* Ar */
-	{ termp_cd_pre, NULL }, /* Cd */
+	{ termp_fd_pre, NULL }, /* Cd */
 	{ termp_bold_pre, NULL }, /* Cm */
 	{ termp_li_pre, NULL }, /* Dv */
-	{ termp_er_pre, NULL }, /* Er */
-	{ termp_tag_pre, NULL }, /* Ev */
+	{ NULL, NULL }, /* Er */
+	{ NULL, NULL }, /* Ev */
 	{ termp_ex_pre, NULL }, /* Ex */
 	{ termp_fa_pre, NULL }, /* Fa */
 	{ termp_fd_pre, termp_fd_post }, /* Fd */
@@ -189,7 +187,7 @@ static const struct mdoc_term_act mdoc_term_acts[MDOC_MAX - MDOC_Dd] = {
 	{ termp_quote_pre, termp_quote_post }, /* Dq */
 	{ NULL, NULL }, /* Ec */ /* FIXME: no space */
 	{ NULL, NULL }, /* Ef */
-	{ termp_em_pre, NULL }, /* Em */
+	{ termp_under_pre, NULL }, /* Em */
 	{ termp_eo_pre, termp_eo_post }, /* Eo */
 	{ termp_xx_pre, termp_xx_post }, /* Fx */
 	{ termp_bold_pre, NULL }, /* Ms */
@@ -212,7 +210,7 @@ static const struct mdoc_term_act mdoc_term_acts[MDOC_MAX - MDOC_Dd] = {
 	{ termp_quote_pre, termp_quote_post }, /* Sq */
 	{ termp_sm_pre, NULL }, /* Sm */
 	{ termp_under_pre, NULL }, /* Sx */
-	{ termp_sy_pre, NULL }, /* Sy */
+	{ termp_bold_pre, NULL }, /* Sy */
 	{ NULL, NULL }, /* Tn */
 	{ termp_xx_pre, termp_xx_post }, /* Ux */
 	{ NULL, NULL }, /* Xc */
@@ -244,8 +242,6 @@ static const struct mdoc_term_act mdoc_term_acts[MDOC_MAX - MDOC_Dd] = {
 	{ termp_skip_pre, NULL }, /* Tg */
 };
 
-static	int	 fn_prio = TAG_STRONG;
-
 
 void
 terminal_mdoc(void *arg, const struct roff_meta *mdoc)
@@ -298,7 +294,6 @@ terminal_mdoc(void *arg, const struct roff_meta *mdoc)
 static void
 print_mdoc_nodelist(DECL_ARGS)
 {
-
 	while (n != NULL) {
 		print_mdoc_node(p, pair, meta, n);
 		n = n->next;
@@ -339,8 +334,7 @@ print_mdoc_node(DECL_ARGS)
 	npair.ppair = pair;
 
 	if (n->flags & NODE_ID)
-		tag_put(n->string == NULL ? n->child->string : n->string,
-		    TAG_MANUAL, p->line);
+		term_tag_write(n, p->line);
 
 	/*
 	 * Keeps only work until the end of a line.  If a keep was
@@ -1006,24 +1000,30 @@ termp_nm_pre(DECL_ARGS)
 			p->flags |= TERMP_HANG;
 		}
 	}
-
-	term_fontpush(p, TERMFONT_BOLD);
-	return 1;
+	return termp_bold_pre(p, pair, meta, n);
 }
 
 static void
 termp_nm_post(DECL_ARGS)
 {
-
-	if (n->type == ROFFT_BLOCK) {
+	switch (n->type) {
+	case ROFFT_BLOCK:
 		p->flags &= ~(TERMP_KEEP | TERMP_PREKEEP);
-	} else if (n->type == ROFFT_HEAD &&
-	    NULL != n->next && NULL != n->next->child) {
+		break;
+	case ROFFT_HEAD:
+		if (n->next == NULL || n->next->child == NULL)
+			break;
 		term_flushln(p);
 		p->flags &= ~(TERMP_NOBREAK | TERMP_BRIND | TERMP_HANG);
 		p->trailspace = 0;
-	} else if (n->type == ROFFT_BODY && n->child != NULL)
-		term_flushln(p);
+		break;
+	case ROFFT_BODY:
+		if (n->child != NULL)
+			term_flushln(p);
+		break;
+	default:
+		break;
+	}
 }
 
 static int
@@ -1031,7 +1031,6 @@ termp_fl_pre(DECL_ARGS)
 {
 	struct roff_node *nn;
 
-	termp_tag_pre(p, pair, meta, n);
 	term_fontpush(p, TERMFONT_BOLD);
 	term_word(p, "\\-");
 
@@ -1217,24 +1216,22 @@ synopsis_pre(struct termp *p, struct roff_node *n)
 static int
 termp_vt_pre(DECL_ARGS)
 {
-
-	if (n->type == ROFFT_ELEM) {
-		synopsis_pre(p, n);
-		return termp_under_pre(p, pair, meta, n);
-	} else if (n->type == ROFFT_BLOCK) {
+	switch (n->type) {
+	case ROFFT_ELEM:
+		return termp_ft_pre(p, pair, meta, n);
+	case ROFFT_BLOCK:
 		synopsis_pre(p, n);
 		return 1;
-	} else if (n->type == ROFFT_HEAD)
+	case ROFFT_HEAD:
 		return 0;
-
-	return termp_under_pre(p, pair, meta, n);
+	default:
+		return termp_under_pre(p, pair, meta, n);
+	}
 }
 
 static int
 termp_bold_pre(DECL_ARGS)
 {
-
-	termp_tag_pre(p, pair, meta, n);
 	term_fontpush(p, TERMFONT_BOLD);
 	return 1;
 }
@@ -1242,7 +1239,6 @@ termp_bold_pre(DECL_ARGS)
 static int
 termp_fd_pre(DECL_ARGS)
 {
-
 	synopsis_pre(p, n);
 	return termp_bold_pre(p, pair, meta, n);
 }
@@ -1250,7 +1246,6 @@ termp_fd_pre(DECL_ARGS)
 static void
 termp_fd_post(DECL_ARGS)
 {
-
 	term_newln(p);
 }
 
@@ -1271,23 +1266,14 @@ termp_sh_pre(DECL_ARGS)
 			term_vspace(p);
 		break;
 	case ROFFT_HEAD:
-		term_fontpush(p, TERMFONT_BOLD);
-		break;
+		return termp_bold_pre(p, pair, meta, n);
 	case ROFFT_BODY:
 		p->tcol->offset = term_len(p, p->defindent);
 		term_tab_set(p, NULL);
 		term_tab_set(p, "T");
 		term_tab_set(p, ".5i");
-		switch (n->sec) {
-		case SEC_DESCRIPTION:
-			fn_prio = TAG_STRONG;
-			break;
-		case SEC_AUTHORS:
+		if (n->sec == SEC_AUTHORS)
 			p->flags &= ~(TERMP_SPLIT|TERMP_NOSPLIT);
-			break;
-		default:
-			break;
-		}
 		break;
 	default:
 		break;
@@ -1298,7 +1284,6 @@ termp_sh_pre(DECL_ARGS)
 static void
 termp_sh_post(DECL_ARGS)
 {
-
 	switch (n->type) {
 	case ROFFT_HEAD:
 		term_newln(p);
@@ -1315,15 +1300,13 @@ termp_sh_post(DECL_ARGS)
 static void
 termp_lb_post(DECL_ARGS)
 {
-
-	if (SEC_LIBRARY == n->sec && NODE_LINE & n->flags)
+	if (n->sec == SEC_LIBRARY && n->flags & NODE_LINE)
 		term_newln(p);
 }
 
 static int
 termp_d1_pre(DECL_ARGS)
 {
-
 	if (n->type != ROFFT_BLOCK)
 		return 1;
 	term_newln(p);
@@ -1337,11 +1320,8 @@ termp_d1_pre(DECL_ARGS)
 static int
 termp_ft_pre(DECL_ARGS)
 {
-
-	/* NB: NODE_LINE does not effect this! */
 	synopsis_pre(p, n);
-	term_fontpush(p, TERMFONT_UNDER);
-	return 1;
+	return termp_under_pre(p, pair, meta, n);
 }
 
 static int
@@ -1350,11 +1330,9 @@ termp_fn_pre(DECL_ARGS)
 	size_t		 rmargin = 0;
 	int		 pretty;
 
-	pretty = NODE_SYNPRETTY & n->flags;
-
 	synopsis_pre(p, n);
-
-	if (NULL == (n = n->child))
+	pretty = n->flags & NODE_SYNPRETTY;
+	if ((n = n->child) == NULL)
 		return 0;
 
 	if (pretty) {
@@ -1368,9 +1346,6 @@ termp_fn_pre(DECL_ARGS)
 	term_word(p, n->string);
 	term_fontpop(p);
 
-	if (n->sec == SEC_DESCRIPTION || n->sec == SEC_CUSTOM)
-		tag_put(n->string, fn_prio++, p->line);
-
 	if (pretty) {
 		term_flushln(p);
 		p->flags &= ~(TERMP_NOBREAK | TERMP_BRIND | TERMP_HANG);
@@ -1405,7 +1380,6 @@ termp_fn_pre(DECL_ARGS)
 		term_word(p, ";");
 		term_flushln(p);
 	}
-
 	return 0;
 }
 
@@ -1414,10 +1388,9 @@ termp_fa_pre(DECL_ARGS)
 {
 	const struct roff_node	*nn;
 
-	if (n->parent->tok != MDOC_Fo) {
-		term_fontpush(p, TERMFONT_UNDER);
-		return 1;
-	}
+	if (n->parent->tok != MDOC_Fo)
+		return termp_under_pre(p, pair, meta, n);
+
 	for (nn = n->child; nn != NULL; nn = nn->next) {
 		term_fontpush(p, TERMFONT_UNDER);
 		p->flags |= TERMP_NBRWORD;
@@ -1528,9 +1501,8 @@ termp_ss_pre(DECL_ARGS)
 			term_vspace(p);
 		break;
 	case ROFFT_HEAD:
-		term_fontpush(p, TERMFONT_BOLD);
 		p->tcol->offset = term_len(p, (p->defindent+1)/2);
-		break;
+		return termp_bold_pre(p, pair, meta, n);
 	case ROFFT_BODY:
 		p->tcol->offset = term_len(p, p->defindent);
 		term_tab_set(p, NULL);
@@ -1551,21 +1523,10 @@ termp_ss_post(DECL_ARGS)
 }
 
 static int
-termp_cd_pre(DECL_ARGS)
-{
-
-	synopsis_pre(p, n);
-	term_fontpush(p, TERMFONT_BOLD);
-	return 1;
-}
-
-static int
 termp_in_pre(DECL_ARGS)
 {
-
 	synopsis_pre(p, n);
-
-	if (NODE_SYNPRETTY & n->flags && NODE_LINE & n->flags) {
+	if (n->flags & NODE_SYNPRETTY && n->flags & NODE_LINE) {
 		term_fontpush(p, TERMFONT_BOLD);
 		term_word(p, "#include");
 		term_word(p, "<");
@@ -1573,7 +1534,6 @@ termp_in_pre(DECL_ARGS)
 		term_word(p, "<");
 		term_fontpush(p, TERMFONT_UNDER);
 	}
-
 	p->flags |= TERMP_NOSPACE;
 	return 1;
 }
@@ -1581,21 +1541,17 @@ termp_in_pre(DECL_ARGS)
 static void
 termp_in_post(DECL_ARGS)
 {
-
-	if (NODE_SYNPRETTY & n->flags)
+	if (n->flags & NODE_SYNPRETTY)
 		term_fontpush(p, TERMFONT_BOLD);
-
 	p->flags |= TERMP_NOSPACE;
 	term_word(p, ">");
-
-	if (NODE_SYNPRETTY & n->flags)
+	if (n->flags & NODE_SYNPRETTY)
 		term_fontpop(p);
 }
 
 static int
 termp_pp_pre(DECL_ARGS)
 {
-	fn_prio = TAG_STRONG;
 	term_vspace(p);
 	return 0;
 }
@@ -1603,14 +1559,12 @@ termp_pp_pre(DECL_ARGS)
 static int
 termp_skip_pre(DECL_ARGS)
 {
-
 	return 0;
 }
 
 static int
 termp_quote_pre(DECL_ARGS)
 {
-
 	if (n->type != ROFFT_BODY && n->type != ROFFT_ELEM)
 		return 1;
 
@@ -1767,17 +1721,15 @@ termp_eo_post(DECL_ARGS)
 static int
 termp_fo_pre(DECL_ARGS)
 {
-	size_t		 rmargin = 0;
-	int		 pretty;
-
-	pretty = NODE_SYNPRETTY & n->flags;
+	size_t rmargin;
 
-	if (n->type == ROFFT_BLOCK) {
+	switch (n->type) {
+	case ROFFT_BLOCK:
 		synopsis_pre(p, n);
 		return 1;
-	} else if (n->type == ROFFT_BODY) {
-		if (pretty) {
-			rmargin = p->tcol->rmargin;
+	case ROFFT_BODY:
+		rmargin = p->tcol->rmargin;
+		if (n->flags & NODE_SYNPRETTY) {
 			p->tcol->rmargin = p->tcol->offset + term_len(p, 4);
 			p->flags |= TERMP_NOBREAK | TERMP_BRIND |
 					TERMP_HANG;
@@ -1785,7 +1737,7 @@ termp_fo_pre(DECL_ARGS)
 		p->flags |= TERMP_NOSPACE;
 		term_word(p, "(");
 		p->flags |= TERMP_NOSPACE;
-		if (pretty) {
+		if (n->flags & NODE_SYNPRETTY) {
 			term_flushln(p);
 			p->flags &= ~(TERMP_NOBREAK | TERMP_BRIND |
 					TERMP_HANG);
@@ -1794,30 +1746,21 @@ termp_fo_pre(DECL_ARGS)
 			p->tcol->rmargin = rmargin;
 		}
 		return 1;
+	default:
+		return termp_bold_pre(p, pair, meta, n);
 	}
-
-	if (NULL == n->child)
-		return 0;
-
-	/* XXX: we drop non-initial arguments as per groff. */
-
-	assert(n->child->string);
-	term_fontpush(p, TERMFONT_BOLD);
-	term_word(p, n->child->string);
-	return 0;
 }
 
 static void
 termp_fo_post(DECL_ARGS)
 {
-
 	if (n->type != ROFFT_BODY)
 		return;
 
 	p->flags |= TERMP_NOSPACE;
 	term_word(p, ")");
 
-	if (NODE_SYNPRETTY & n->flags) {
+	if (n->flags & NODE_SYNPRETTY) {
 		p->flags |= TERMP_NOSPACE;
 		term_word(p, ";");
 		term_flushln(p);
@@ -1827,29 +1770,30 @@ termp_fo_post(DECL_ARGS)
 static int
 termp_bf_pre(DECL_ARGS)
 {
-
-	if (n->type == ROFFT_HEAD)
+	switch (n->type) {
+	case ROFFT_HEAD:
 		return 0;
-	else if (n->type != ROFFT_BODY)
+	case ROFFT_BODY:
+		break;
+	default:
 		return 1;
-
-	if (FONT_Em == n->norm->Bf.font)
-		term_fontpush(p, TERMFONT_UNDER);
-	else if (FONT_Sy == n->norm->Bf.font)
-		term_fontpush(p, TERMFONT_BOLD);
-	else
-		term_fontpush(p, TERMFONT_NONE);
-
-	return 1;
+	}
+	switch (n->norm->Bf.font) {
+	case FONT_Em:
+		return termp_under_pre(p, pair, meta, n);
+	case FONT_Sy:
+		return termp_bold_pre(p, pair, meta, n);
+	default:
+		return termp_li_pre(p, pair, meta, n);
+	}
 }
 
 static int
 termp_sm_pre(DECL_ARGS)
 {
-
-	if (NULL == n->child)
+	if (n->child == NULL)
 		p->flags ^= TERMP_NONOSPACE;
-	else if (0 == strcmp("on", n->child->string))
+	else if (strcmp(n->child->string, "on") == 0)
 		p->flags &= ~TERMP_NONOSPACE;
 	else
 		p->flags |= TERMP_NONOSPACE;
@@ -1863,7 +1807,6 @@ termp_sm_pre(DECL_ARGS)
 static int
 termp_ap_pre(DECL_ARGS)
 {
-
 	p->flags |= TERMP_NOSPACE;
 	term_word(p, "'");
 	p->flags |= TERMP_NOSPACE;
@@ -1902,8 +1845,6 @@ termp____post(DECL_ARGS)
 static int
 termp_li_pre(DECL_ARGS)
 {
-
-	termp_tag_pre(p, pair, meta, n);
 	term_fontpush(p, TERMFONT_NONE);
 	return 1;
 }
@@ -1953,7 +1894,6 @@ termp_lk_pre(DECL_ARGS)
 static int
 termp_bk_pre(DECL_ARGS)
 {
-
 	switch (n->type) {
 	case ROFFT_BLOCK:
 		break;
@@ -1966,107 +1906,47 @@ termp_bk_pre(DECL_ARGS)
 	default:
 		abort();
 	}
-
 	return 1;
 }
 
 static void
 termp_bk_post(DECL_ARGS)
 {
-
 	if (n->type == ROFFT_BODY)
 		p->flags &= ~(TERMP_KEEP | TERMP_PREKEEP);
 }
 
+/*
+ * If we are in an `Rs' and there is a journal present,
+ * then quote us instead of underlining us (for disambiguation).
+ */
 static void
 termp__t_post(DECL_ARGS)
 {
-
-	/*
-	 * If we're in an `Rs' and there's a journal present, then quote
-	 * us instead of underlining us (for disambiguation).
-	 */
-	if (n->parent && MDOC_Rs == n->parent->tok &&
+	if (n->parent != NULL && n->parent->tok == MDOC_Rs &&
 	    n->parent->norm->Rs.quote_T)
 		termp_quote_post(p, pair, meta, n);
-
 	termp____post(p, pair, meta, n);
 }
 
 static int
 termp__t_pre(DECL_ARGS)
 {
-
-	/*
-	 * If we're in an `Rs' and there's a journal present, then quote
-	 * us instead of underlining us (for disambiguation).
-	 */
-	if (n->parent && MDOC_Rs == n->parent->tok &&
+	if (n->parent != NULL && n->parent->tok == MDOC_Rs &&
 	    n->parent->norm->Rs.quote_T)
 		return termp_quote_pre(p, pair, meta, n);
-
-	term_fontpush(p, TERMFONT_UNDER);
-	return 1;
+	else
+		return termp_under_pre(p, pair, meta, n);
 }
 
 static int
 termp_under_pre(DECL_ARGS)
 {
-
-	term_fontpush(p, TERMFONT_UNDER);
-	return 1;
-}
-
-static int
-termp_em_pre(DECL_ARGS)
-{
-	if (n->child != NULL &&
-	    n->child->type == ROFFT_TEXT)
-		tag_put(n->child->string, TAG_FALLBACK, p->line);
 	term_fontpush(p, TERMFONT_UNDER);
 	return 1;
 }
 
 static int
-termp_sy_pre(DECL_ARGS)
-{
-	if (n->child != NULL &&
-	    n->child->type == ROFFT_TEXT)
-		tag_put(n->child->string, TAG_FALLBACK, p->line);
-	term_fontpush(p, TERMFONT_BOLD);
-	return 1;
-}
-
-static int
-termp_er_pre(DECL_ARGS)
-{
-
-	if (n->sec == SEC_ERRORS &&
-	    (n->parent->tok == MDOC_It ||
-	     (n->parent->tok == MDOC_Bq &&
-	      n->parent->parent->parent->tok == MDOC_It)))
-		tag_put(n->child->string, TAG_STRONG, p->line);
-	return 1;
-}
-
-static int
-termp_tag_pre(DECL_ARGS)
-{
-
-	if (n->child != NULL &&
-	    n->child->type == ROFFT_TEXT &&
-	    (n->prev == NULL ||
-	     (n->prev->type == ROFFT_TEXT &&
-	      strcmp(n->prev->string, "|") == 0)) &&
-	    (n->parent->tok == MDOC_It ||
-	     (n->parent->tok == MDOC_Xo &&
-	      n->parent->parent->prev == NULL &&
-	      n->parent->parent->parent->tok == MDOC_It)))
-		tag_put(n->child->string, TAG_STRONG, p->line);
-	return 1;
-}
-
-static int
 termp_abort_pre(DECL_ARGS)
 {
 	abort();
diff --git a/usr.bin/mandoc/mdoc_validate.c b/usr.bin/mandoc/mdoc_validate.c
index 033a368cd75..c5497fb87f2 100644
--- a/usr.bin/mandoc/mdoc_validate.c
+++ b/usr.bin/mandoc/mdoc_validate.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: mdoc_validate.c,v 1.294 2020/02/27 21:38:27 schwarze Exp $ */
+/* $OpenBSD: mdoc_validate.c,v 1.295 2020/03/13 00:31:05 schwarze Exp $ */
 /*
- * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010 Joerg Sonnenberger <joerg@netbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
@@ -15,6 +15,8 @@
  * 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.
+ *
+ * Validation module for mdoc(7) syntax trees used by mandoc(1).
  */
 #include <sys/types.h>
 #ifndef OSNAME
@@ -33,6 +35,7 @@
 #include "mandoc.h"
 #include "mandoc_xr.h"
 #include "roff.h"
+#include "tag.h"
 #include "mdoc.h"
 #include "libmandoc.h"
 #include "roff_int.h"
@@ -80,7 +83,9 @@ static	void	 post_dd(POST_ARGS);
 static	void	 post_delim(POST_ARGS);
 static	void	 post_delim_nb(POST_ARGS);
 static	void	 post_dt(POST_ARGS);
+static	void	 post_em(POST_ARGS);
 static	void	 post_en(POST_ARGS);
+static	void	 post_er(POST_ARGS);
 static	void	 post_es(POST_ARGS);
 static	void	 post_eoln(POST_ARGS);
 static	void	 post_ex(POST_ARGS);
@@ -111,6 +116,7 @@ static	void	 post_sm(POST_ARGS);
 static	void	 post_st(POST_ARGS);
 static	void	 post_std(POST_ARGS);
 static	void	 post_sx(POST_ARGS);
+static	void	 post_tag(POST_ARGS);
 static	void	 post_tg(POST_ARGS);
 static	void	 post_useless(POST_ARGS);
 static	void	 post_xr(POST_ARGS);
@@ -135,19 +141,19 @@ static	const v_post mdoc_valids[MDOC_MAX - MDOC_Dd] = {
 	NULL,		/* Ap */
 	post_defaults,	/* Ar */
 	NULL,		/* Cd */
-	post_delim_nb,	/* Cm */
-	post_delim_nb,	/* Dv */
-	post_delim_nb,	/* Er */
-	post_delim_nb,	/* Ev */
+	post_tag,	/* Cm */
+	post_tag,	/* Dv */
+	post_er,	/* Er */
+	post_tag,	/* Ev */
 	post_ex,	/* Ex */
 	post_fa,	/* Fa */
 	NULL,		/* Fd */
-	post_delim_nb,	/* Fl */
+	post_tag,	/* Fl */
 	post_fn,	/* Fn */
 	post_delim_nb,	/* Ft */
-	post_delim_nb,	/* Ic */
+	post_tag,	/* Ic */
 	post_delim_nb,	/* In */
-	post_defaults,	/* Li */
+	post_tag,	/* Li */
 	post_nd,	/* Nd */
 	post_nm,	/* Nm */
 	post_delim_nb,	/* Op */
@@ -185,11 +191,11 @@ static	const v_post mdoc_valids[MDOC_MAX - MDOC_Dd] = {
 	NULL,		/* Dq */
 	NULL,		/* Ec */
 	NULL,		/* Ef */
-	post_delim_nb,	/* Em */
+	post_em,	/* Em */
 	NULL,		/* Eo */
 	post_xx,	/* Fx */
-	post_delim_nb,	/* Ms */
-	NULL,		/* No */
+	post_tag,	/* Ms */
+	post_tag,	/* No */
 	post_ns,	/* Ns */
 	post_xx,	/* Nx */
 	post_xx,	/* Ox */
@@ -208,7 +214,7 @@ static	const v_post mdoc_valids[MDOC_MAX - MDOC_Dd] = {
 	post_delim_nb,	/* Sq */
 	post_sm,	/* Sm */
 	post_sx,	/* Sx */
-	post_delim_nb,	/* Sy */
+	post_em,	/* Sy */
 	post_useless,	/* Tn */
 	post_xx,	/* Ux */
 	NULL,		/* Xc */
@@ -285,6 +291,8 @@ static	const char * const secnames[SEC__MAX] = {
 	NULL
 };
 
+static	int	  fn_prio = TAG_STRONG;
+
 
 /* Validate the subtree rooted at mdoc->last. */
 void
@@ -1079,8 +1087,11 @@ post_st(POST_ARGS)
 static void
 post_tg(POST_ARGS)
 {
-	struct roff_node	*n, *nch, *nn;
-	size_t			len;
+	struct roff_node *n;	/* The .Tg node. */
+	struct roff_node *nch;	/* The first child of the .Tg node. */
+	struct roff_node *nn;   /* The next node after the .Tg node. */
+	struct roff_node *nt;	/* The TEXT node containing the tag. */
+	size_t		  len;	/* The number of bytes in the tag. */
 
 	/* Find the next node. */
 	n = mdoc->last;
@@ -1091,30 +1102,26 @@ post_tg(POST_ARGS)
 		}
 	}
 
-	/* Add the default argument, if needed. */
-	nch = n->child;
-	if (nch == NULL && nn != NULL && nn->child->type == ROFFT_TEXT) {
-		mdoc->next = ROFF_NEXT_CHILD;
-		roff_word_alloc(mdoc, n->line, n->pos, n->next->child->string);
-		nch = mdoc->last;
-		nch->flags |= NODE_NOSRC;
-		mdoc->last = n;
-	}
+	/* Find the tag. */
+	nt = nch = n->child;
+	if (nch == NULL && nn != NULL && nn->child != NULL &&
+	    nn->child->type == ROFFT_TEXT)
+		nt = nn->child;
 
-	/* Validate the first argument. */
-	if (nch == NULL || *nch->string == '\0')
+	/* Validate the tag. */
+	if (nt == NULL || *nt->string == '\0')
 		mandoc_msg(MANDOCERR_MACRO_EMPTY, n->line, n->pos, "Tg");
-	if (nch == NULL) {
+	if (nt == NULL) {
 		roff_node_delete(mdoc, n);
 		return;
 	}
-	len = strcspn(nch->string, " \t");
-	if (nch->string[len] != '\0')
-		mandoc_msg(MANDOCERR_TG_SPC, nch->line, nch->pos + len + 1,
-		    "Tg %s", nch->string);
+	len = strcspn(nt->string, " \t\\");
+	if (nt->string[len] != '\0')
+		mandoc_msg(MANDOCERR_TG_SPC, nt->line,
+		    nt->pos + len, "Tg %s", nt->string);
 
 	/* Keep only the first argument. */
-	if (nch->next != NULL) {
+	if (nch != NULL && nch->next != NULL) {
 		mandoc_msg(MANDOCERR_ARG_EXCESS, nch->next->line,
 		    nch->next->pos, "Tg ... %s", nch->next->string);
 		while (nch->next != NULL)
@@ -1122,32 +1129,44 @@ post_tg(POST_ARGS)
 	}
 
 	/* Drop the macro if the first argument is invalid. */
-	if (len == 0 || nch->string[len] != '\0') {
+	if (len == 0 || nt->string[len] != '\0') {
 		roff_node_delete(mdoc, n);
 		return;
 	}
 
-	/* By default, write a <mark> element. */
-	n->flags |= NODE_ID;
+	/* By default, tag the .Tg node itself. */
 	if (nn == NULL)
-		return;
+		nn = n;
 
 	/* Explicit tagging of specific macros. */
 	switch (nn->tok) {
 	case MDOC_Sh:
 	case MDOC_Ss:
-		if (nn->head->flags & NODE_ID || nn->head->child == NULL)
+	case MDOC_Fo:
+		nn = nn->head;
+		/* FALLTHROUGH */
+	case MDOC_Cm:
+	case MDOC_Dv:
+	case MDOC_Em:
+	case MDOC_Er:
+	case MDOC_Ev:
+	case MDOC_Fl:
+	case MDOC_Fn:
+	case MDOC_Ic:
+	case MDOC_Li:
+	case MDOC_Ms:
+	case MDOC_No:
+	case MDOC_Sy:
+		if (nn->child != NULL && (nn->flags & NODE_ID) == 0)
 			break;
-		n->flags |= NODE_NOPRT;
-		nn->head->flags |= NODE_ID | NODE_HREF;
-		assert(nn->head->string == NULL);
-		nn->head->string = mandoc_strdup(nch->string);
-		break;
+		/* FALLTHROUGH */
 	default:
+		nn = n;
 		break;
 	}
-	if (n->flags & NODE_NOPRT)
-		n->flags &= ~NODE_ID;
+	tag_put(nt->string, TAG_MANUAL, nn);
+	if (nn != n)
+		n->flags |= NODE_NOPRT;
 }
 
 static void
@@ -1242,28 +1261,32 @@ post_bf(POST_ARGS)
 static void
 post_fname(POST_ARGS)
 {
-	const struct roff_node	*n;
+	struct roff_node	*n, *nch;
 	const char		*cp;
 	size_t			 pos;
 
-	n = mdoc->last->child;
-	cp = n->string;
+	n = mdoc->last;
+	nch = n->child;
+	cp = nch->string;
 	if (*cp == '(') {
 		if (cp[strlen(cp + 1)] == ')')
 			return;
 		pos = 0;
 	} else {
 		pos = strcspn(cp, "()");
-		if (cp[pos] == '\0')
+		if (cp[pos] == '\0') {
+			if (n->sec == SEC_DESCRIPTION ||
+			    n->sec == SEC_CUSTOM)
+				tag_put(NULL, fn_prio++, n);
 			return;
+		}
 	}
-	mandoc_msg(MANDOCERR_FN_PAREN, n->line, n->pos + pos, "%s", cp);
+	mandoc_msg(MANDOCERR_FN_PAREN, nch->line, nch->pos + pos, "%s", cp);
 }
 
 static void
 post_fn(POST_ARGS)
 {
-
 	post_fname(mdoc);
 	post_fa(mdoc);
 }
@@ -1427,38 +1450,29 @@ post_display(POST_ARGS)
 static void
 post_defaults(POST_ARGS)
 {
-	struct roff_node *nn;
+	struct roff_node *n;
 
-	if (mdoc->last->child != NULL) {
+	n = mdoc->last;
+	if (n->child != NULL) {
 		post_delim_nb(mdoc);
 		return;
 	}
-
-	/*
-	 * The `Ar' defaults to "file ..." if no value is provided as an
-	 * argument; the `Mt' and `Pa' macros use "~"; the `Li' just
-	 * gets an empty string.
-	 */
-
-	nn = mdoc->last;
-	switch (nn->tok) {
+	mdoc->next = ROFF_NEXT_CHILD;
+	switch (n->tok) {
 	case MDOC_Ar:
-		mdoc->next = ROFF_NEXT_CHILD;
-		roff_word_alloc(mdoc, nn->line, nn->pos, "file");
-		mdoc->last->flags |= NODE_NOSRC;
-		roff_word_alloc(mdoc, nn->line, nn->pos, "...");
+		roff_word_alloc(mdoc, n->line, n->pos, "file");
 		mdoc->last->flags |= NODE_NOSRC;
+		roff_word_alloc(mdoc, n->line, n->pos, "...");
 		break;
 	case MDOC_Pa:
 	case MDOC_Mt:
-		mdoc->next = ROFF_NEXT_CHILD;
-		roff_word_alloc(mdoc, nn->line, nn->pos, "~");
-		mdoc->last->flags |= NODE_NOSRC;
+		roff_word_alloc(mdoc, n->line, n->pos, "~");
 		break;
 	default:
 		abort();
 	}
-	mdoc->last = nn;
+	mdoc->last->flags |= NODE_NOSRC;
+	mdoc->last = n;
 }
 
 static void
@@ -1512,18 +1526,54 @@ post_an(POST_ARGS)
 }
 
 static void
-post_en(POST_ARGS)
+post_em(POST_ARGS)
 {
+	post_tag(mdoc);
+	tag_put(NULL, TAG_FALLBACK, mdoc->last);
+}
 
+static void
+post_en(POST_ARGS)
+{
 	post_obsolete(mdoc);
 	if (mdoc->last->type == ROFFT_BLOCK)
 		mdoc->last->norm->Es = mdoc->last_es;
 }
 
 static void
-post_es(POST_ARGS)
+post_er(POST_ARGS)
+{
+	struct roff_node *n;
+
+	n = mdoc->last;
+	if (n->sec == SEC_ERRORS &&
+	    (n->parent->tok == MDOC_It ||
+	     (n->parent->tok == MDOC_Bq &&
+	      n->parent->parent->parent->tok == MDOC_It)))
+		tag_put(NULL, TAG_STRONG, n);
+	post_delim_nb(mdoc);
+}
+
+static void
+post_tag(POST_ARGS)
 {
+	struct roff_node *n;
+
+	n = mdoc->last;
+	if ((n->prev == NULL ||
+	     (n->prev->type == ROFFT_TEXT &&
+	      strcmp(n->prev->string, "|") == 0)) &&
+	    (n->parent->tok == MDOC_It ||
+	     (n->parent->tok == MDOC_Xo &&
+	      n->parent->parent->prev == NULL &&
+	      n->parent->parent->parent->tok == MDOC_It)))
+		tag_put(NULL, TAG_STRONG, n);
+	post_delim_nb(mdoc);
+}
 
+static void
+post_es(POST_ARGS)
+{
 	post_obsolete(mdoc);
 	mdoc->last_es = mdoc->last;
 }
@@ -1620,8 +1670,8 @@ post_it(POST_ARGS)
 		if ((nch = nit->head->child) != NULL)
 			mandoc_msg(MANDOCERR_ARG_SKIP,
 			    nit->line, nit->pos, "It %s",
-			    nch->string == NULL ? roff_name[nch->tok] :
-			    nch->string);
+			    nch->type == ROFFT_TEXT ? nch->string :
+			    roff_name[nch->tok]);
 		break;
 	case LIST_column:
 		cols = (int)nbl->norm->Bl.ncols;
@@ -2137,7 +2187,6 @@ post_sx(POST_ARGS)
 static void
 post_sh(POST_ARGS)
 {
-
 	post_ignpar(mdoc);
 
 	switch (mdoc->last->type) {
@@ -2369,6 +2418,8 @@ post_sh_head(POST_ARGS)
 		roff_setreg(mdoc->roff, "nS", 0, '=');
 		mdoc->flags &= ~MDOC_SYNOPSIS;
 	}
+	if (sec == SEC_DESCRIPTION)
+		fn_prio = TAG_STRONG;
 
 	/* Mark our last section. */
 
@@ -2540,6 +2591,7 @@ post_par(POST_ARGS)
 {
 	struct roff_node *np;
 
+	fn_prio = TAG_STRONG;
 	post_prevpar(mdoc);
 
 	np = mdoc->last;
diff --git a/usr.bin/mandoc/read.c b/usr.bin/mandoc/read.c
index 6dfe2003abd..a32274c5d0a 100644
--- a/usr.bin/mandoc/read.c
+++ b/usr.bin/mandoc/read.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: read.c,v 1.185 2019/07/10 19:38:56 schwarze Exp $ */
+/* $OpenBSD: read.c,v 1.186 2020/03/13 00:31:05 schwarze Exp $ */
 /*
- * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010-2019 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010, 2012 Joerg Sonnenberger <joerg@netbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
@@ -15,6 +15,12 @@
  * 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.
+ *
+ * Top-level functions of the mandoc(3) parser:
+ * Parser and input encoding selection, decompression,
+ * handling of input bytes, characters, lines, and files,
+ * handling of roff(7) loops and file inclusion,
+ * and steering of the various parsers.
  */
 #include <sys/types.h>
 #include <sys/mman.h>
@@ -34,6 +40,7 @@
 #include "mandoc_aux.h"
 #include "mandoc.h"
 #include "roff.h"
+#include "tag.h"
 #include "mdoc.h"
 #include "man.h"
 #include "mandoc_parse.h"
@@ -662,6 +669,7 @@ mparse_alloc(int options, enum mandoc_os os_e, const char *os_s)
 	}
 	curp->man->meta.first->tok = TOKEN_NONE;
 	curp->man->meta.os_e = os_e;
+	tag_alloc();
 	return curp;
 }
 
@@ -678,6 +686,7 @@ mparse_reset(struct mparse *curp)
 void
 mparse_free(struct mparse *curp)
 {
+	tag_free();
 	roffhash_free(curp->man->mdocmac);
 	roffhash_free(curp->man->manmac);
 	roff_man_free(curp->man);
diff --git a/usr.bin/mandoc/tag.c b/usr.bin/mandoc/tag.c
index 5c0854315dd..8bdf9943597 100644
--- a/usr.bin/mandoc/tag.c
+++ b/usr.bin/mandoc/tag.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tag.c,v 1.27 2020/01/20 10:29:31 schwarze Exp $ */
+/* $OpenBSD: tag.c,v 1.28 2020/03/13 00:31:05 schwarze Exp $ */
 /*
  * Copyright (c) 2015,2016,2018,2019,2020 Ingo Schwarze <schwarze@openbsd.org>
  *
@@ -13,132 +13,65 @@
  * 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.
+ *
+ * Functions to tag syntax tree nodes.
+ * For internal use by mandoc(1) validation modules only.
  */
 #include <sys/types.h>
 
 #include <assert.h>
-#include <errno.h>
 #include <limits.h>
-#include <signal.h>
 #include <stddef.h>
-#include <stdint.h>
-#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <unistd.h>
 
 #include "mandoc_aux.h"
 #include "mandoc_ohash.h"
-#include "mandoc.h"
+#include "roff.h"
 #include "tag.h"
 
 struct tag_entry {
-	size_t	*lines;
-	size_t	 maxlines;
-	size_t	 nlines;
+	struct roff_node **nodes;
+	size_t	 maxnodes;
+	size_t	 nnodes;
 	int	 prio;
 	char	 s[];
 };
 
-static	void	 tag_signal(int) __attribute__((__noreturn__));
-
 static struct ohash	 tag_data;
-static struct tag_files	 tag_files;
 
 
 /*
- * Prepare for using a pager.
- * Not all pagers are capable of using a tag file,
- * but for simplicity, create it anyway.
+ * Set up the ohash table to collect nodes
+ * where various marked-up terms are documented.
  */
-struct tag_files *
-tag_init(char *tagname)
+void
+tag_alloc(void)
 {
-	struct sigaction	 sa;
-	int			 ofd;
-
-	ofd = -1;
-	tag_files.tfd = -1;
-	tag_files.tcpgid = -1;
-	tag_files.tagname = tagname;
-
-	/* Clean up when dying from a signal. */
-
-	memset(&sa, 0, sizeof(sa));
-	sigfillset(&sa.sa_mask);
-	sa.sa_handler = tag_signal;
-	sigaction(SIGHUP, &sa, NULL);
-	sigaction(SIGINT, &sa, NULL);
-	sigaction(SIGTERM, &sa, NULL);
-
-	/*
-	 * POSIX requires that a process calling tcsetpgrp(3)
-	 * from the background gets a SIGTTOU signal.
-	 * In that case, do not stop.
-	 */
-
-	sa.sa_handler = SIG_IGN;
-	sigaction(SIGTTOU, &sa, NULL);
-
-	/* Save the original standard output for use by the pager. */
-
-	if ((tag_files.ofd = dup(STDOUT_FILENO)) == -1) {
-		mandoc_msg(MANDOCERR_DUP, 0, 0, "%s", strerror(errno));
-		goto fail;
-	}
+	mandoc_ohash_init(&tag_data, 4, offsetof(struct tag_entry, s));
+}
 
-	/* Create both temporary output files. */
+void
+tag_free(void)
+{
+	struct tag_entry	*entry;
+	unsigned int		 slot;
 
-	(void)strlcpy(tag_files.ofn, "/tmp/man.XXXXXXXXXX",
-	    sizeof(tag_files.ofn));
-	(void)strlcpy(tag_files.tfn, "/tmp/man.XXXXXXXXXX",
-	    sizeof(tag_files.tfn));
-	if ((ofd = mkstemp(tag_files.ofn)) == -1) {
-		mandoc_msg(MANDOCERR_MKSTEMP, 0, 0,
-		    "%s: %s", tag_files.ofn, strerror(errno));
-		goto fail;
-	}
-	if ((tag_files.tfd = mkstemp(tag_files.tfn)) == -1) {
-		mandoc_msg(MANDOCERR_MKSTEMP, 0, 0,
-		    "%s: %s", tag_files.tfn, strerror(errno));
-		goto fail;
-	}
-	if (dup2(ofd, STDOUT_FILENO) == -1) {
-		mandoc_msg(MANDOCERR_DUP, 0, 0, "%s", strerror(errno));
-		goto fail;
+	entry = ohash_first(&tag_data, &slot);
+	while (entry != NULL) {
+		free(entry->nodes);
+		free(entry);
+		entry = ohash_next(&tag_data, &slot);
 	}
-	close(ofd);
-
-	/*
-	 * Set up the ohash table to collect output line numbers
-	 * where various marked-up terms are documented.
-	 */
-
-	mandoc_ohash_init(&tag_data, 4, offsetof(struct tag_entry, s));
-	return &tag_files;
-
-fail:
-	tag_unlink();
-	if (ofd != -1)
-		close(ofd);
-	if (tag_files.ofd != -1)
-		close(tag_files.ofd);
-	if (tag_files.tfd != -1)
-		close(tag_files.tfd);
-	*tag_files.ofn = '\0';
-	*tag_files.tfn = '\0';
-	tag_files.ofd = -1;
-	tag_files.tfd = -1;
-	tag_files.tagname = NULL;
-	return NULL;
+	ohash_delete(&tag_data);
 }
 
 /*
- * Set the line number where a term is defined,
+ * Set a node where a term is defined,
  * unless it is already defined at a lower priority.
  */
 void
-tag_put(const char *s, int prio, size_t line)
+tag_put(const char *s, int prio, struct roff_node *n)
 {
 	struct tag_entry	*entry;
 	const char		*se;
@@ -146,11 +79,14 @@ tag_put(const char *s, int prio, size_t line)
 	unsigned int		 slot;
 
 	assert(prio <= TAG_FALLBACK);
-	if (tag_files.tfd <= 0)
-		return;
 
-	if (s[0] == '\\' && (s[1] == '&' || s[1] == 'e'))
-		s += 2;
+	if (s == NULL) {
+		if (n->child == NULL || n->child->type != ROFFT_TEXT)
+			return;
+		s = n->child->string;
+		if (s[0] == '\\' && (s[1] == '&' || s[1] == 'e'))
+			s += 2;
+	}
 
 	/*
 	 * Skip whitespace and escapes and whatever follows,
@@ -168,131 +104,67 @@ tag_put(const char *s, int prio, size_t line)
 	slot = ohash_qlookupi(&tag_data, s, &se);
 	entry = ohash_find(&tag_data, slot);
 
-	if (entry == NULL) {
-
-		/* Build a new entry. */
+	/* Build a new entry. */
 
+	if (entry == NULL) {
 		entry = mandoc_malloc(sizeof(*entry) + len + 1);
 		memcpy(entry->s, s, len);
 		entry->s[len] = '\0';
-		entry->lines = NULL;
-		entry->maxlines = entry->nlines = 0;
+		entry->nodes = NULL;
+		entry->maxnodes = entry->nnodes = 0;
 		ohash_insert(&tag_data, slot, entry);
+	}
 
-	} else {
-
-		/*
-		 * Lower priority numbers take precedence,
-		 * but TAG_FALLBACK is special.
-		 * A tag with priority TAG_FALLBACK is only used
-		 * if the tag occurs exactly once.
-		 */
+	/*
+	 * Lower priority numbers take precedence.
+	 * If a better entry is already present, ignore the new one.
+	 */
 
-		if (prio == TAG_FALLBACK) {
-			if (entry->prio == TAG_FALLBACK)
-				entry->prio = TAG_DELETE;
+	else if (entry->prio < prio)
 			return;
-		}
 
-		/* A better entry is already present, ignore the new one. */
-
-		if (entry->prio < prio)
-			return;
+	/*
+	 * If the existing entry is worse, clear it.
+	 * In addition, a tag with priority TAG_FALLBACK
+	 * is only used if the tag occurs exactly once.
+	 */
 
-		/* The existing entry is worse, clear it. */
+	else if (entry->prio > prio || prio == TAG_FALLBACK) {
+		while (entry->nnodes > 0)
+			entry->nodes[--entry->nnodes]->flags &= ~NODE_ID;
 
-		if (entry->prio > prio)
-			entry->nlines = 0;
+		if (prio == TAG_FALLBACK) {
+			entry->prio = TAG_DELETE;
+			return;
+		}
 	}
 
-	/* Remember the new line. */
+	/* Remember the new node. */
 
-	if (entry->maxlines == entry->nlines) {
-		entry->maxlines += 4;
-		entry->lines = mandoc_reallocarray(entry->lines,
-		    entry->maxlines, sizeof(*entry->lines));
+	if (entry->maxnodes == entry->nnodes) {
+		entry->maxnodes += 4;
+		entry->nodes = mandoc_reallocarray(entry->nodes,
+		    entry->maxnodes, sizeof(*entry->nodes));
 	}
-	entry->lines[entry->nlines++] = line;
+	entry->nodes[entry->nnodes++] = n;
 	entry->prio = prio;
-}
-
-/*
- * Write out the tags file using the previously collected
- * information and clear the ohash table while going along.
- */
-void
-tag_write(void)
-{
-	FILE			*stream;
-	struct tag_entry	*entry;
-	size_t			 i;
-	unsigned int		 slot;
-	int			 empty;
-
-	if (tag_files.tfd <= 0)
-		return;
-	if (tag_files.tagname != NULL && ohash_find(&tag_data,
-            ohash_qlookup(&tag_data, tag_files.tagname)) == NULL) {
-		mandoc_msg(MANDOCERR_TAG, 0, 0, "%s", tag_files.tagname);
-		tag_files.tagname = NULL;
-	}
-	if ((stream = fdopen(tag_files.tfd, "w")) == NULL)
-		mandoc_msg(MANDOCERR_FDOPEN, 0, 0, "%s", strerror(errno));
-	empty = 1;
-	entry = ohash_first(&tag_data, &slot);
-	while (entry != NULL) {
-		if (stream != NULL && entry->prio < TAG_DELETE) {
-			for (i = 0; i < entry->nlines; i++) {
-				fprintf(stream, "%s %s %zu\n",
-				    entry->s, tag_files.ofn, entry->lines[i]);
-				empty = 0;
-			}
-		}
-		free(entry->lines);
-		free(entry);
-		entry = ohash_next(&tag_data, &slot);
-	}
-	ohash_delete(&tag_data);
-	if (stream != NULL)
-		fclose(stream);
-	else
-		close(tag_files.tfd);
-	tag_files.tfd = -1;
-	if (empty) {
-		unlink(tag_files.tfn);
-		*tag_files.tfn = '\0';
+	n->flags |= NODE_ID;
+	if (n->child == NULL || n->child->string != s || *se != '\0') {
+		assert(n->string == NULL);
+		n->string = mandoc_strndup(s, len);
 	}
 }
 
-void
-tag_unlink(void)
+enum tag_result
+tag_check(const char *test_tag)
 {
-	pid_t	 tc_pgid;
+	unsigned int slot;
 
-	if (tag_files.tcpgid != -1) {
-		tc_pgid = tcgetpgrp(tag_files.ofd);
-		if (tc_pgid == tag_files.pager_pid ||
-		    tc_pgid == getpgid(0) ||
-		    getpgid(tc_pgid) == -1)
-			(void)tcsetpgrp(tag_files.ofd, tag_files.tcpgid);
-	}
-	if (*tag_files.ofn != '\0')
-		unlink(tag_files.ofn);
-	if (*tag_files.tfn != '\0')
-		unlink(tag_files.tfn);
-}
-
-static void
-tag_signal(int signum)
-{
-	struct sigaction	 sa;
-
-	tag_unlink();
-	memset(&sa, 0, sizeof(sa));
-	sigemptyset(&sa.sa_mask);
-	sa.sa_handler = SIG_DFL;
-	sigaction(signum, &sa, NULL);
-	kill(getpid(), signum);
-	/* NOTREACHED */
-	_exit(1);
+	if (ohash_first(&tag_data, &slot) == NULL)
+		return TAG_EMPTY;
+	else if (test_tag != NULL && ohash_find(&tag_data,
+	    ohash_qlookup(&tag_data, test_tag)) == NULL)
+		return TAG_MISS;
+	else
+		return TAG_OK;
 }
diff --git a/usr.bin/mandoc/tag.h b/usr.bin/mandoc/tag.h
index a4a4128eef0..494b72bb2ca 100644
--- a/usr.bin/mandoc/tag.h
+++ b/usr.bin/mandoc/tag.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: tag.h,v 1.10 2020/01/20 10:29:31 schwarze Exp $    */
+/* $OpenBSD: tag.h,v 1.11 2020/03/13 00:31:05 schwarze Exp $ */
 /*
  * Copyright (c) 2015, 2018, 2019, 2020 Ingo Schwarze <schwarze@openbsd.org>
  *
@@ -13,6 +13,9 @@
  * 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 to tag syntax tree nodes.
+ * For use by mandoc(1) validation modules only.
  */
 
 /*
@@ -25,19 +28,17 @@
 #define	TAG_FALLBACK	(INT_MAX - 1)	/* Tag only used if unique. */
 #define	TAG_DELETE	(INT_MAX)	/* Tag not used at all. */
 
-
-struct	tag_files {
-	char	 ofn[20];
-	char	 tfn[20];
-	char	*tagname;
-	int	 ofd;
-	int	 tfd;
-	pid_t	 tcpgid;
-	pid_t	 pager_pid;
+/*
+ * Return values of tag_check().
+ */
+enum tag_result {
+	TAG_OK,		/* Argument exists as a tag. */
+	TAG_MISS,	/* Argument not found. */
+	TAG_EMPTY	/* No tag exists at all. */
 };
 
 
-struct tag_files *tag_init(char *);
-void	 tag_put(const char *, int, size_t);
-void	 tag_write(void);
-void	 tag_unlink(void);
+void		 tag_alloc(void);
+void		 tag_put(const char *, int, struct roff_node *);
+enum tag_result	 tag_check(const char *);
+void		 tag_free(void);
diff --git a/usr.bin/mandoc/term_tag.c b/usr.bin/mandoc/term_tag.c
new file mode 100644
index 00000000000..9a15b562036
--- /dev/null
+++ b/usr.bin/mandoc/term_tag.c
@@ -0,0 +1,204 @@
+/* $OpenBSD: term_tag.c,v 1.1 2020/03/13 00:31:05 schwarze Exp $ */
+/*
+ * Copyright (c) 2015,2016,2018,2019,2020 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.
+ *
+ * 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.
+ *
+ * Functions to write a ctags(1) file.
+ * For use by the mandoc(1) ASCII and UTF-8 formatters only.
+ */
+#include <sys/types.h>
+
+#include <errno.h>
+#include <signal.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "mandoc.h"
+#include "roff.h"
+#include "tag.h"
+#include "term_tag.h"
+
+static void tag_signal(int) __attribute__((__noreturn__));
+
+static struct tag_files tag_files;
+
+
+/*
+ * Prepare for using a pager.
+ * Not all pagers are capable of using a tag file,
+ * but for simplicity, create it anyway.
+ */
+struct tag_files *
+term_tag_init(char *tagname)
+{
+	struct sigaction	 sa;
+	int			 ofd;	/* In /tmp/, dup(2)ed to stdout. */
+	int			 tfd;
+
+	ofd = tfd = -1;
+	tag_files.tfs = NULL;
+	tag_files.tcpgid = -1;
+	tag_files.tagname = tagname;
+
+	/* Clean up when dying from a signal. */
+
+	memset(&sa, 0, sizeof(sa));
+	sigfillset(&sa.sa_mask);
+	sa.sa_handler = tag_signal;
+	sigaction(SIGHUP, &sa, NULL);
+	sigaction(SIGINT, &sa, NULL);
+	sigaction(SIGTERM, &sa, NULL);
+
+	/*
+	 * POSIX requires that a process calling tcsetpgrp(3)
+	 * from the background gets a SIGTTOU signal.
+	 * In that case, do not stop.
+	 */
+
+	sa.sa_handler = SIG_IGN;
+	sigaction(SIGTTOU, &sa, NULL);
+
+	/* Save the original standard output for use by the pager. */
+
+	if ((tag_files.ofd = dup(STDOUT_FILENO)) == -1) {
+		mandoc_msg(MANDOCERR_DUP, 0, 0, "%s", strerror(errno));
+		goto fail;
+	}
+
+	/* Create both temporary output files. */
+
+	(void)strlcpy(tag_files.ofn, "/tmp/man.XXXXXXXXXX",
+	    sizeof(tag_files.ofn));
+	(void)strlcpy(tag_files.tfn, "/tmp/man.XXXXXXXXXX",
+	    sizeof(tag_files.tfn));
+	if ((ofd = mkstemp(tag_files.ofn)) == -1) {
+		mandoc_msg(MANDOCERR_MKSTEMP, 0, 0,
+		    "%s: %s", tag_files.ofn, strerror(errno));
+		goto fail;
+	}
+	if ((tfd = mkstemp(tag_files.tfn)) == -1) {
+		mandoc_msg(MANDOCERR_MKSTEMP, 0, 0,
+		    "%s: %s", tag_files.tfn, strerror(errno));
+		goto fail;
+	}
+	if ((tag_files.tfs = fdopen(tfd, "w")) == NULL) {
+		mandoc_msg(MANDOCERR_FDOPEN, 0, 0, "%s", strerror(errno));
+		goto fail;
+	}
+	tfd = -1;
+	if (dup2(ofd, STDOUT_FILENO) == -1) {
+		mandoc_msg(MANDOCERR_DUP, 0, 0, "%s", strerror(errno));
+		goto fail;
+	}
+	close(ofd);
+	return &tag_files;
+
+fail:
+	term_tag_unlink();
+	if (ofd != -1)
+		close(ofd);
+	if (tfd != -1)
+		close(tfd);
+	if (tag_files.ofd != -1) {
+		close(tag_files.ofd);
+		tag_files.ofd = -1;
+	}
+	tag_files.tagname = NULL;
+	return NULL;
+}
+
+void
+term_tag_write(struct roff_node *n, size_t line)
+{
+	const char	*cp;
+	int		 len;
+
+	if (tag_files.tfs == NULL)
+		return;
+	if (n->string == NULL)
+		n = n->child;
+	cp = n->string;
+	if (cp[0] == '\\' && (cp[1] == '&' || cp[1] == 'e'))
+		cp += 2;
+	len = strcspn(cp, " \t\\");
+	fprintf(tag_files.tfs, "%.*s %s %zu\n",
+	    len, cp, tag_files.ofn, line);
+}
+
+void
+term_tag_finish(void)
+{
+	if (tag_files.tfs == NULL)
+		return;
+	fclose(tag_files.tfs);
+	tag_files.tfs = NULL;
+	switch (tag_check(tag_files.tagname)) {
+	case TAG_EMPTY:
+		unlink(tag_files.tfn);
+		*tag_files.tfn = '\0';
+		/* FALLTHROUGH */
+	case TAG_MISS:
+		if (tag_files.tagname == NULL)
+			break;
+		mandoc_msg(MANDOCERR_TAG, 0, 0, "%s", tag_files.tagname);
+		tag_files.tagname = NULL;
+		break;
+	case TAG_OK:
+		break;
+	}
+}
+
+void
+term_tag_unlink(void)
+{
+	pid_t	 tc_pgid;
+
+	if (tag_files.tcpgid != -1) {
+		tc_pgid = tcgetpgrp(tag_files.ofd);
+		if (tc_pgid == tag_files.pager_pid ||
+		    tc_pgid == getpgid(0) ||
+		    getpgid(tc_pgid) == -1)
+			(void)tcsetpgrp(tag_files.ofd, tag_files.tcpgid);
+	}
+	if (*tag_files.ofn != '\0') {
+		unlink(tag_files.ofn);
+		*tag_files.ofn = '\0';
+	}
+	if (*tag_files.tfn != '\0') {
+		unlink(tag_files.tfn);
+		*tag_files.tfn = '\0';
+	}
+	if (tag_files.tfs != NULL) {
+		fclose(tag_files.tfs);
+		tag_files.tfs = NULL;
+	}
+}
+
+static void
+tag_signal(int signum)
+{
+	struct sigaction	 sa;
+
+	term_tag_unlink();
+	memset(&sa, 0, sizeof(sa));
+	sigemptyset(&sa.sa_mask);
+	sa.sa_handler = SIG_DFL;
+	sigaction(signum, &sa, NULL);
+	kill(getpid(), signum);
+	/* NOTREACHED */
+	_exit(1);
+}
diff --git a/usr.bin/mandoc/term_tag.h b/usr.bin/mandoc/term_tag.h
new file mode 100644
index 00000000000..d1f31c4fba4
--- /dev/null
+++ b/usr.bin/mandoc/term_tag.h
@@ -0,0 +1,35 @@
+/* $OpenBSD: term_tag.h,v 1.1 2020/03/13 00:31:05 schwarze Exp $ */
+/*
+ * Copyright (c) 2015, 2018, 2019, 2020 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.
+ *
+ * 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.
+ *
+ * Internal interfaces to write a ctags(1) file.
+ * For use by the mandoc(1) ASCII and UTF-8 formatters only.
+ */
+
+struct	tag_files {
+	char	 ofn[20];	/* Output file name. */
+	char	 tfn[20];	/* Tag file name. */
+	char	*tagname;	/* Target specified with -O. */
+	FILE	*tfs;		/* Tag file object. */
+	int	 ofd;		/* Original output file descriptor. */
+	pid_t	 tcpgid;	/* Process group controlling the terminal. */
+	pid_t	 pager_pid;	/* Process ID of the pager. */
+};
+
+
+struct tag_files	*term_tag_init(char *);
+void			 term_tag_write(struct roff_node *, size_t);
+void			 term_tag_finish(void);
+void			 term_tag_unlink(void);
diff --git a/usr.bin/mandoc/tree.c b/usr.bin/mandoc/tree.c
index cc123ccf308..5d82f866056 100644
--- a/usr.bin/mandoc/tree.c
+++ b/usr.bin/mandoc/tree.c
@@ -1,7 +1,7 @@
-/*	$OpenBSD: tree.c,v 1.53 2020/02/27 21:38:27 schwarze Exp $ */
+/* $OpenBSD: tree.c,v 1.54 2020/03/13 00:31:05 schwarze Exp $ */
 /*
- * Copyright (c) 2008, 2009, 2011, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2013-2015, 2017-2020 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2008, 2009, 2011, 2014 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
@@ -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.
+ *
+ * Formatting module to let mandoc(1) show
+ * a human readable representation of the syntax tree.
  */
 #include <sys/types.h>
 
@@ -303,6 +306,11 @@ print_man(const struct roff_node *n, int indent)
 			putchar(')');
 		if (n->flags & NODE_EOS)
 			putchar('.');
+		if (n->flags & NODE_ID) {
+			printf(" ID");
+			if (n->string != NULL)
+				printf("=%s", n->string);
+		}
 		if (n->flags & NODE_NOFILL)
 			printf(" NOFILL");
 		putchar('\n');