Introduce the concept of nodes that are semantically transparent:

they are skipped when looking for previous or following high-level
macros.  Examples include roff(7) .ft, .ll, and .ta, mdoc(7) .Sm
and .Tg, and man(7) .DT and .PD.  Use this concept for a variety
of improved decisions in various validators and formatters.

While here,
* remove a few const qualifiers on struct arguments that caused trouble;
* get rid of some more Yoda notation in the vicinity;
* and apply some other stylistic improvements in the vicinity.

I found this class of issues while considering .Tg patches from kn@.

4 files changed, 81 insertions, 2 deletions

diff --git a/regress/mdoc/Rs/Makefile b/regress/mdoc/Rs/Makefile
index 2881b874..e6e3e1bc 100644
--- a/regress/mdoc/Rs/Makefile
+++ b/regress/mdoc/Rs/Makefile
@@ -1,6 +1,6 @@
-# $OpenBSD: Makefile,v 1.11 2019/01/07 06:51:37 schwarze Exp $
+# $OpenBSD: Makefile,v 1.12 2020/02/27 01:25:58 schwarze Exp $
 
-REGRESS_TARGETS	 = allch args break empty paragraph three_authors
+REGRESS_TARGETS	 = allch args break empty paragraph three_authors transp
 UTF8_TARGETS	 = allch break empty three_authors
 LINT_TARGETS	 = allch args empty
 HTML_TARGETS	 = paragraph
diff --git a/regress/mdoc/Rs/transp.in b/regress/mdoc/Rs/transp.in
new file mode 100644
index 00000000..7e906d00
--- /dev/null
+++ b/regress/mdoc/Rs/transp.in
@@ -0,0 +1,36 @@
+.\" $OpenBSD: transp.in,v 1.1 2020/02/27 01:25:58 schwarze Exp $
+.Dd $Mdocdate: February 27 2020 $
+.Dt RS-TRANSPARENT 1
+.Os
+.Sh NAME
+.Nm Rs-transparent
+.Nd transparent nodes in reference blocks
+.Sh SEE ALSO
+.Tg transparent
+.Rs
+.%T title
+.%A first after title
+.%A last
+.Re
+.Rs
+.%A first
+.%A middle
+.%A last before title
+.%T title
+.Re
+.Rs
+.%T title
+.Tg transparent
+.%A first after title and transparent
+.%A middle before transparent
+.Tg transparent
+.%A last before transparent
+.Tg transparent
+.Re
+.Rs
+.Tg transparent
+.%A first after transparent
+.%A last before transparent and title
+.Tg transparent
+.%T title
+.Re
diff --git a/regress/mdoc/Rs/transp.out_ascii b/regress/mdoc/Rs/transp.out_ascii
new file mode 100644
index 00000000..cc217ed5
--- /dev/null
+++ b/regress/mdoc/Rs/transp.out_ascii
@@ -0,0 +1,16 @@
+RS-TRANSPARENT(1)           General Commands Manual          RS-TRANSPARENT(1)
+
+NNAAMMEE
+     RRss--ttrraannssppaarreenntt - transparent nodes in reference blocks
+
+SSEEEE AALLSSOO
+     first after title and last, _t_i_t_l_e.
+
+     first, middle, and last before title, _t_i_t_l_e.
+
+     first after title and transparent, middle before transparent, and last
+     before transparent, _t_i_t_l_e.
+
+     first after transparent and last before transparent and title, _t_i_t_l_e.
+
+OpenBSD                        February 27, 2020                       OpenBSD
diff --git a/regress/mdoc/Rs/transp.out_markdown b/regress/mdoc/Rs/transp.out_markdown
new file mode 100644
index 00000000..a9896335
--- /dev/null
+++ b/regress/mdoc/Rs/transp.out_markdown
@@ -0,0 +1,27 @@
+RS-TRANSPARENT(1) - General Commands Manual
+
+# NAME
+
+**Rs-transparent** - transparent nodes in reference blocks
+
+# SEE ALSO
+
+first after title,
+last,
+*title*.
+
+first,
+middle, and
+last before title,
+*title*.
+
+first after title and transparent,
+middle before transparent, and
+last before transparent,
+*title*.
+
+first after transparent,
+last before transparent and title,
+*title*.
+
+OpenBSD - February 27, 2020