Follow-up Comment #3, bug #59434 (group groff):
[comment #0 original submission:]
> Consensus on the email list (thread starting at
http://lists.gnu.org/archive/html/groff/2020-09/msg00000.html)
I'm afraid I have to depart from this consensus, given recent study in this
area; see bug #45502 and bug #65474.
> is that
>
> .if COND1 .ie COND2 xxx
> . el yyy
>
> is not a legal construction (or rather, is only legal when COND1 is true).
I claim that it's valid regardless of the truth value of COND1, and all *roff
formatters we've studied reliably produce the same results given it (for my
part, that's Unix V7, Solaris 10, DWB 3.3, and _groff_ from 1.22.3 to the
present day).
> But the documentation does not make this clear, saying the part after the
condition in an .if request "is interpreted as though it were on a line by
itself." Were the .ie in fact on a line by itself, groff wouldn't emit an
"unbalanced .el request" warning when COND1 is false.
That's a problem with the warning diagnostic being an insufficiently powerful
interpreter of _roff_ input when skipping over a branch not taken. It doesn't
"see" that `ie`, even in the absence of an immediately following `\{`, creates
a new "level" of conditional with which coupling of a subsequent `el` request
is expected.
> Further down the email thread, Branden writes a lengthy analysis why .if
"hides" an .ie but processes \{ and \}. While informative, hopefully there is
a more succinct way to explain this in the groff documentation.
And indeed I've tried to explain it several more times in the ticket traffic
of the last few days.
If I hit upon a presentation that you find persuasive, I'll likely weight that
heavily when considering what language to add to our Texinfo manual to
deobfuscate this matter.
Though I hope that just shutting up the spurious "unbalanced 'el'" warnings
will do considerable work toward that goal.
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