Any unknown header is treated as an Entity-Header, and a proxy must cache
entity headers if it intends to forward them to future clients.
>I would prefer if caches would not cache objects that contained unknown
>headers under any conditions. If this can't be the case, can we at least
>have a requirement that caches must not cache responses that carry protocol
>versions whose defined elements aren't understood by the cache.
That is unneccessary if the recipient compares the received headers
to the received HTTP-Version.
....Roy T. Fielding Department of ICS, University of California, Irvine USA
Visiting Scholar, MIT/LCS + World-Wide Web Consortium