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Re: Conditional Content.

From: Ian B. Jacobs <ij@w3.org>
Date: Fri, 23 Aug 2002 09:26:47 -0400
Message-ID: <3D663817.6070607@w3.org>
To: Jim Ley <jim@jibbering.com>
CC: w3c-wai-ua@w3.org

Jim Ley wrote:
> Hi,
> Firstly congratulations on UAAG 1.0 it looks great, I've got no
> criticisms of it.

Thanks Jim!

> I just have a question about 2.3 - Render Conditional Content.
> In SVG, there are the foriegnObject, and metadata elements, both of which
> allow content to be included with pretty much any semantics at all.  So
> does 2.3 require that a SVG User Agent, render conditional content
> included in a foreignObject or in Metadata elements, that it doesn't know
> the semantics of (and so how to render sensibly.)

Conditional content is defined by specification. For the most
part, UAAG 1.0 says "if you recognize it and it's part of
a claim, you are responsible for it." In some cases (e.g.,
blinking text, image control), UAAG 1.0 says "if you recognize
it and even if it's not part of a claim, you are responsible for

If the content of the foreignObject is defined by specification S,
and S says that it's conditional content, and the user agent
implements S, then the user agent is responsible for making
it available. The "user agent" may include a plug-in specifically
for this rendering.

Otherwise, if the user agent does not implement S or does
not recognize the content as being conditional, it's not responsible
for knowing that it's conditional content. Per checkpoint 2.1,
the user agent is responsible for following specifications for
rendering, so if the content is xml and has associated style sheets,
and the user agent implements xml+style sheets, then the user
agent is again responsible for proper handling.

> For example, http://jibbering.com/2002/8/static.svg is a simple SVG file,
> containing just a raster image, with a title and description, and a
> metadata element which describes the image in some detail, however it's
> using my own semantics so we can't really expect another user agent to be
> able to use it( http://jibbering.com/2002/8/img-desc.svg is what I do
> with it.)

Where do you define your own semantics?

> The same with foreignObject in SVG, are you expecting that an SVG UA
> should render the XHTML or PDF, or whatever representation that is
> included via foriegnObject (but not normally displayed due to switch.) ?

No, the user agent is not responsible for rendering all formats. You
can define your user agent to encompass as many formats as you wish:
if your user agent consists of an SVG agent and a PDF agent, then
it's responsible for both. Otherwise, you can claim conformance for
the SVG part alone.

Please let me know whether this is clear enough,

  - Ian

Ian Jacobs (ij@w3.org)   http://www.w3.org/People/Jacobs
Tel:                     +1 718 260-9447
Received on Friday, 23 August 2002 09:41:35 UTC

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