#fillin

[Rob Beezer]

Mostly for Alex.

We have #fillin that live inside math, and #fillin that live outside math. I
think largely to represent "answer blanks" for interactive questions in static
formats.

While deprecating math elements, I ended up editing a bunch of identical tests
for in-math vs outside-math.

How about doing that test *once* per #fillin in the pre-processor, and dropping
a "pi:" attribute? I've been doing more and more of that. Interpret different
scenarios once, and let the attribute provide the result across all conversions.

@pi:authored-in-math?

With values "yes" or "no". Or perhaps simply present (pi:authored-in-math="")
or not present (). I just did that to distinguish the two forms of #md
(one-line v. structured with #mrow).

Maybe in the "repair" phase? Are you up for a PR to that effect?

Rob