(1) In the definition of the Accept request header, there is no
mention of a "version" modifier, e.g.,
Accept: text/html; version=3.0
This would seem like the right way to determine HTML client
capabilities. Going by the User-Agent field is a real quagmire.
(2) The semantics of Expires should discourage clients from
_indiscriminately_ trying to refetch objects, just because they have
expired. Dynamically-created pages can be ephemeral, without having
time-dependent content that needs to be updated.
For example, the Geometry Center interactive gallery generates
dynamic graphical HTML pages customized to each user's request. The
user's images are deleted at the same moment they are fetched, and so
the document ceases to exist on the server the moment it is
retrieved. Therefore, the gallery expires all documents immediately:
Expires: Sun, 01 Jan 0000 00:00:00 GMT
Nevertheless, it would not make sense to try to fetch an "updated"
version of such a document.
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Paul Burchard <burchard@math.utah.edu>
``I'm still learning how to count backwards from infinity...''
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