Re: Initializing HTTP headers from HTML documents

Dave_Raggett (
Thu, 6 Jan 94 10:40:54 GMT

John Ellson writes:

> I agree that authors would like to expire their documents at some
> point in the future, even if those documents are being served
> from a cache site. But I don't see how a timestamp is sufficiently
> expressive of the reasons an author might have to expire a document.
> The reasons might not even be known at the time that the document
> is written.

> Could VALUE be a boolean expression so that we could do something like:


> or:

> <META NAME="Expires" VALUE=GT(DATE, "Tue, 04 Jan 1994 14:13:25 GMT")>

It would be better to use a different attribute name than VALUE if the server
needs to evaluate some expression to compute the value string. I would
suggest EVAL. Note that the definition of Expires: is given in the HTTP
spec and is derived from the its use in News articles. So in this case
the expression must result in a date in the HTTP date format.

Since EVAL expressions would be evaluated by the server, it seems reasonable
to come up with a consensus approach like CGI to ensure a degree of
standardisation. Would you like to come up with a proposal?

Dave Raggett