RE: i37: Vary and non-existant headers

Mark Nottingham wrote:
> http://tools.ietf.org/wg/httpbis/trac/ticket/37
> 
> Roy sort-of proposed deleting "present" in 
> <http://lists.w3.org/Archives/Public/ietf-http-wg/2006OctDec/0090.html
>  >
> 
> In addition, I'd propose:
> 
> * adding: "When a resource's representations vary, an origin 
> server SHOULD include the Vary header even when the selecting 
> header(s) are not present; otherwise, caches will use that 
> representation inappropriately."

I think it would be better to say: "For each request URI, an origin server
SHOULD return the same Vary header field value for every request." In this
way, the Vary header is not just a response header but a "resource header".

> * adding: "Caches MAY canonicalise request headers before 
> comparing them for purposes of determining whether they match 
> during variant selection."

Clients, intermediaries, and servers should always be able to canonicalize
headers in any situation. Putting a specific statement about it here imples
there are some cases in which canonicalization is not allowed. I suggest
leaving this part out.

- Brian