I like this one a lot, couldn't be more to the point! Thanks Marc and
Daphne!

I've read the whole document and don't see any problems. But on the
abstract I think `define-optionals` and `define-optionals*` should be
mentioned as well, like the `let` counterparts. It would give the whole
view of the SRFI to a newcomer right away.

If I get a bit of time to try the implementation I'll report back too.

OT: Maybe it was already mentioned previously and I missed it, but will
there be a follow-up for keyword arguments?