Masking and IPv6

Just two little questions for whoever is working on the detailed mask proposals
(I lose track).

Did I miss the post where it was explained how 16-octet IPv6 address masks are
to be encoded and distinguished from IPv4 masks?

And is it defined what happens if the receiver has an IPv6 address to test, and
a mask is expressed only in IPv4, and vice versa?

Chris Haynes