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@.

1 files changed, 44 insertions, 0 deletions

diff --git a/regress/mdoc/blank/transp.out_markdown b/regress/mdoc/blank/transp.out_markdown
new file mode 100644
index 00000000..9c8ac825
--- /dev/null
+++ b/regress/mdoc/blank/transp.out_markdown
@@ -0,0 +1,44 @@
+BLANK-TRANSP(1) - General Commands Manual
+
+# NAME
+
+**blank-transp** - transparent nodes between line breaks
+
+# DESCRIPTION
+
+Double br:  
+br Pp:
+
+Pp br:
+
+Double Pp:
+
+br sp:
+
+sp br:
+
+Pp sp:
+
+Pp sp 2v:
+
+sp Pp:
+
+Double sp:
+
+br blank:
+
+blank br:
+
+Pp blank:
+
+blank Pp:
+
+sp blank:
+
+blank sp:
+
+Double blank:
+
+end of file
+
+OpenBSD - February 27, 2020