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, 77 insertions, 0 deletions

diff --git a/regress/mdoc/blank/transp.in b/regress/mdoc/blank/transp.in
new file mode 100644
index 00000000..0e58bf2e
--- /dev/null
+++ b/regress/mdoc/blank/transp.in
@@ -0,0 +1,77 @@
+.\" $OpenBSD: transp.in,v 1.1 2020/02/27 01:25:59 schwarze Exp $
+.Dd $Mdocdate$
+.Dt BLANK-TRANSP 1
+.Os
+.Sh NAME
+.Nm blank-transp
+.Nd transparent nodes between line breaks
+.Sh DESCRIPTION
+Double br:
+.br
+.Tg brbr
+.br
+br Pp:
+.br
+.Tg brPp
+.Pp
+Pp br:
+.Pp
+.Tg Ppbr
+.br
+Double Pp:
+.Pp
+.Tg PpPp
+.Pp
+br sp:
+.br
+.Tg brsp
+.sp
+sp br:
+.sp
+.Tg spbr
+.br
+Pp sp:
+.Pp
+.Tg Ppsp
+.sp
+Pp sp 2v:
+.Pp
+.Tg Ppsp2v
+.sp 2v
+sp Pp:
+.sp
+.Tg spPp
+.Pp
+Double sp:
+.sp
+.Tg spsp
+.sp
+br blank:
+.br
+.Tg brbl
+
+blank br:
+
+.Tg blbr
+.br
+Pp blank:
+.Pp
+.Tg Ppbl
+
+blank Pp:
+
+.Tg blPp
+.Pp
+sp blank:
+.sp
+.Tg spbl
+
+blank sp:
+
+.Tg blsp
+.sp
+Double blank:
+
+.Tg blbl
+
+end of file