EWG reflector discussions raised another couple of points, which I had lost
track of:

Tony Van Eerd pointed out that we probably want exceptions escaping from a
transaction to be UB rather than implementation defined, since the
semantics have been regularly debated. We don't really want some
implementations supporting commit, and others abort semantics. Code just
shouldn't rely on that. I tend to agree with that observation.

There was also discussion of somehow providing a capture list for
transactions, as in lambda's. I'm less confident I understand that proposal.

Hans