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, 48 insertions, 0 deletions

diff --git a/regress/mdoc/blank/transp.out_ascii b/regress/mdoc/blank/transp.out_ascii
new file mode 100644
index 00000000..f8bdd6b8
--- /dev/null
+++ b/regress/mdoc/blank/transp.out_ascii
@@ -0,0 +1,48 @@
+BLANK-TRANSP(1)             General Commands Manual            BLANK-TRANSP(1)
+
+NNAAMMEE
+     bbllaannkk--ttrraannsspp - transparent nodes between line breaks
+
+DDEESSCCRRIIPPTTIIOONN
+     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                       OpenBSD