Link: http://trac.tools.ietf.org/wg/httpbis/trac/ticket/39
Origin: http://www.w3.org/mid/1161261658.29399.24.camel@henriknordstrom.net
Component: p4-conditional
From experience I think it's also worthwhile to further stress the importance of ETag uniqueness among variants of a URI. Very few implementations get this part correct. In fact most major web servers have issues here...
Some even strongly believe that entities with different Content-Encoding is the same entity, arguing that since most encoding (at least the standardized ones) can be converted to the same identity encoding so they are in fact the same entity and should have the same strong ETag.
Proposal:
Strong entity tags MUST be unique for each representation of a particular resource; they must change if the representation varies over time and/or because of the use of server-driven content negotiation.
proposal is for inclusion in p4 section 7.1. However, need WG buy-in for adding a new requirement; flipping to design.