think about adding note wrt how client platform might obtain authenticator capabilities

[equalsJeffH]

we state things like "If...the authenticator is not capable of ...", or mention some-or-other authnr "capability", in several places in the spec but do not mention "these are the plausible means for how the [=client platform=] might obtain authenticator capabilities..."

[equalsJeffH]

this is a very minor nice-to-have issue, can be addressed in a milestone later than wd-03 or not at all.