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

From: Ian Hickson <ian@hixie.ch>
Date: Wed, 28 Dec 2005 14:37:13 +0000 (UTC)
To: Chris Lilley <chris@w3.org>
Cc: www-svg@w3.org
Message-ID: <Pine.LNX.4.62.0512281431460.7669@dhalsim.dreamhost.com>

On Tue, 20 Dec 2005, Chris Lilley wrote:
> > The requirements on user agents for mediaCharacterEncoding and 
> > mediaContentEncodings are unclear in the current text.
> >
> > The mediaCharacterEncoding attribute seems to suggest that the value 
> > from this attribute should be used to override any value returned in 
> > the HTTP 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.

That does indeed make more sense, thanks.

> > The mediaContentEncodings attribute does not appear to require any 
> > 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.

There is no requirement that the prefetch hint be used at all. In fact, as 
I mentioned, the mediaContentEncodings attribute does not appear to 
require any behaviour at all on the part of a renderer.

Please clarify the specification so that it is clear what rendering UAs 
may or must not do with these attributes. One way to do this would be to 
include a clear subsection giving the processing model for this element, 
giving the algorithm that must be used to determine how much content to 
prefetch, and then requiring (or allowing) the user agent to perform the 
relevant network requests. Currently this section vaguely mentioned 
possibilities but makes no testable normative requirements on rendering 
user agents.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Wednesday, 28 December 2005 14:37:33 UTC

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