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Re: expires

From: Lee Daniel Crocker <lcrocker@calweb.com>
Date: Wed, 8 May 1996 18:04:26 -0700 (PDT)
Message-Id: <199605090104.SAA09923@web1.calweb.com>
To: www-talk@w3.org
> I'm already sending an Expires header, but I was wondering if that
> header applied to the inline images as well as the containing document
> since those images are retrieved separately.

If it did, that would be a serious bug in your server. If you have
a server full of dynamic news documents, each of which has your
logo on top and fancy bullets, whould you want the user's browser
constantly throwing away those static images just because you've
included them in timely reports?  Images may be _rendered_ inline,
but as far as the server is concerned they are documents in their
own right.

> You are implying that each inline image must be transmitted with its
> own Expires header.  Is this really necessary?  Or are the browsers
> using the containing document's expiration date as a default for the
> inline images?  I would like to think that this is the case.

Yes, it's necessary.  No, a browser should not assume an expiration
date for any document or image just because one happens to reference
or include the other.  If no Expires: header is sent with an image,
it should assume whatever it assumes with normal documents that don't
have an Expires: header. Only the server "knows" when documents or
images become invalid, because it is their "source"; but the server
does not know which images are contained in which documents. It just
blindly sends the document requested as a black box, and the browser
must then parse the HTML and tell the server which images to send.
Received on Wednesday, 8 May 1996 21:04:45 GMT

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