[bug #63812] Discussion of conditional expressions in docs should mention `.if h`

[G. Branden Robinson]

Update of bug #63812 (project groff):

                  Status:                    None => In Progress            

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Follow-up Comment #4:

I'm working on this on a (so far, local only) post-1.23.0 branch.

Here's what I have at the moment.


diff --git a/doc/groff.texi b/doc/groff.texi
index 15b3cd8a3..ae5645c63 100644
--- a/doc/groff.texi
+++ b/doc/groff.texi
@@ -12571,8 +12571,19 @@ certain other @code{troff}
implementations.@footnote{This refers to
 @code{vtroff}, a translator that would convert the C/A/T output from
 early-vintage @acronym{AT&T} @code{troff} to a form suitable for
 Versatec and Benson-Varian plotters.}
+@end table
+
+If the first argument to an @code{if}, @code{ie}, or @code{while}
+request begins with a non-alphanumeric character apart from @code{!}
+(see below); it performs an @slanted{output comparison test}.
+@footnote{Strictly, letters not otherwise recognized @emph{are} treated
+as output comparison delimiters.  For portability, it is wise to avoid
+using letters not in the list above; for example, Plan@tie{}9
+@code{troff} uses @samp{h} to test a mode it calls @code{htmlroff}, and
+GNU @code{troff} may provide additional operators in the future.}
 
 @cindex output comparison operator
+@table @code
 @item @code{'}@var{xxx}@code{'}@var{yyy}@code{'}
 True if formatting the comparands @var{xxx} and @var{yyy} produces the
 same output commands.  The delimiter need not be a neutral apostrophe:
diff --git a/man/groff.7.man b/man/groff.7.man
index 0d0539a98..dec4deefd 100644
--- a/man/groff.7.man
+++ b/man/groff.7.man
@@ -2099,9 +2099,20 @@ T}
 .
 .
 .P
-The first of the above,
+If the first argument to an
+.BR .if ,
+.BR .ie ,
+or
+.B .while
+request begins with a non-alphanumeric character apart from
+.B !\&
+(see below);
+it performs an
+.I "output comparison test" .
+.
+Shown first in the table above,
 the
-.I "output comparison operator,"
+.I "output comparison operator"
 interpolates a true value if formatting its comparands
 .I s1
 and



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