> for example, stuff like the %B specifier are technically optional given
that the uppercase conversion specifier namespace wasn't reserved, but iirc
there's no known implementation of C that uses it for any > other purpose.

     There was apparently one implementation that was already using %B as a
kind of numeric printout (not for binary) that was reported during the
meeting and at a few other junctures, so unfortunately it might not be
fully portable. But, I think that for that implementation it's flag-guarded
(though on by default). It'd be great if I remembered the name of the
implementation (but the meeting this was discussed in was... over a year
ago now? So I'd have to go back and refresh my memory). If I do remember, I
thought to myself that I might send an e-mail asking them if they would
feel okay with aligning their library with the standard's recommendations.
Couldn't hurt to ask, right?

- JeanHeyd