Re: Still trying to make sense of HTTP caching model

According to Shel Kaphan:
> 
> Jeffrey Mogul writes:
> 	...
> 
>  >    2.	Cache this object but always validate before using
>  > 	   (i.e., "Expires: 1 January 1900")
> 
> I see. This actually gives a reasonable meaning to this construct.
> This meaning seems better than simply "don't cache this", and works well with
> GET if-<whatever>.  With plain GET it is equivalent to not caching.
> 	...

This usage encodes some very non-intuitive semantics in the Expires:
heading.  If you want to tell the proxy to cache a document but always
validate it then create a header or Pragma to do that.  Trying to
encode this request in an otherwise meaningless variant of an existing
header is a mistake.  This will inevitably lead to confusion because
most people already think they know what Expires: means and they
have a right to think that.

John Franks