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Re: [SVGMobile12] SVGT12-207: Unclear rules regarding mediaCharacterEncoding and mediaContentEncodings

From: Chris Lilley <chris@w3.org>
Date: Tue, 20 Dec 2005 13:46:08 +0100
Message-ID: <187645365.20051220134608@w3.org>
To: Ian Hickson <ian@hixie.ch>
Cc: www-svg@w3.org

On Tuesday, December 13, 2005, 4:39:33 AM, Ian wrote:

IH> The requirements on user agents for mediaCharacterEncoding and 
IH> mediaContentEncodings are unclear in the current text.

IH> The mediaCharacterEncoding attribute seems to suggest that the value from
IH> this attribute should be used to override any value returned in the HTTP
IH> headers of the media, which seems to violate HTTP's requirements.

We agree that, if that was what the attribute was for, it would conflict
with both HTTP and AWWW. However, that is not what it is for at all.
There is no mention of overriding any value that the server sends.

We suspect that you were misunderstanding the following text

   If the attribute is not specified, the encoding used is that returned
   by the server.

and have reworded it as follows to make it clearer:

    If the attribute is not specified, the encoding that was used to
    calculate the size is that which is returned by the server.

It is important to read the preceding sentence:

   The main use of this attribute is to know what character encoding was
   used when measuring 'mediaSize' so that staleness of the hints may be
   easily detected.

In other words, if the content comes back in a different character
encoding, the size hint is stale and cannot be used.

IH> The mediaContentEncodings attribute does not appear to require any 
IH> behaviour on the part of a renderer, although it hints at possible uses.

We were not sure what you meant by that. If the size was measured with
one media content encoding and the content arrives with a different
media content encoding then clearly the prefetch hint is stale and
cannot be used.

IH> Please clarify the specification so that it is clear what rendering UAs 
IH> may or must not do with these attributes, and so that any suggestion that
IH> they can be used to override authoritative HTTP headers is removed.

We did not find any suggestion that authoritative metadata was
overridden, but hope that the rewording above makes it clearer.

 Chris Lilley                    mailto:chris@w3.org
 Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG
Received on Tuesday, 20 December 2005 12:46:34 UTC

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