EDIT for section 13.3.4

I suggest the the following paragraph from 13.3.4 

        Note: in order to provide semantically transparent caching, an
        origin server should avoid reusing a specific strong opaque
        validator value for two different instances of an entity, or
        reusing a specific weak opaque validator value for two
        semantically different instances of an entity.  Caches entries
        may persist for arbitrarily long periods, regardless of
        expiration times, so it may be inappropriate to expect that a
        cache will never again attempt to validate an entry using a
        validator that it obtained at some point in the past.

be replaced with

   Note: in order to provide semantically transparent caching, an origin
   server should not reuse a strong opaque validator value for an entity
   corresponding to the same resource (URI) as the entity for which the
   validator value was first used, even if the reuse would occur after
   the expiration time of the original entity.  A server should not reuse
   a weak opaque validator value for a semantically different entity
   corresponding to the same resource as the entity for which it was
   first used.  Caches' entries may persist for arbitrarily long periods,
   regardless of expiration times, so it may be inappropriate to expect
   that a cache will never again attempt to validate an entry using a
   validator that it obtained at some point in the past.



John Franks 	Dept of Math. Northwestern University
		john@math.nwu.edu