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Re: [SVGMobile12] Question on SVG implementation in an XLink-aware processor

From: Chris Lilley <chris@w3.org>
Date: Tue, 4 Apr 2006 12:37:29 +0200
Message-ID: <1447705346.20060404123729@w3.org>
To: www-svg@w3.org
Cc: Boris Zbarsky <bzbarsky@mit.edu>

Hello www-svg,

Boris Zbarsky <bzbarsky@mit.edu> wrote:

> Consider the following markup (assuming that the "svg" and "xlink" namespace 
> prefixes are bound to the relevant namespaces):
> 
>    <svg:image xlink:href="something.png" xlink:show="replace"
>               xlink:actuate="onload"/>

Such markup is not conformant to the schema for SVGT 1.2, but I assume
you knew that.

> It would seem to me that correct behavior here for a UA that supports both SVG 
> and XLink would be to replace the page with something.png when this is parsed 
> (as required by the XLink specification), while the correct behavior for a UA 
> that supports SVG but not XLink would be to do whatever the description of 
> <svg:image> says.  Is that correct?

This use of values for show and actuate which are not licensed by the
SVG specification is outside the scope of the SVG specification. Don't
do that. One might as well discuss (again assuming relevant ns
declarations)

<html>
 <head>
   <meta xl:href="something.png" xl:show="embed" xl:actuate="onLoad"/>
 </head>
</html>

or, indeed,

<html>
 <head>
   <meta src="something.png"/>
 </head>
</html>


> Note that I don't think the spec needs changes in this regard, since
> the XLink specification is very clear on what the behavior should be
> in this case. But I just want to make sure that there are no
> assumptions that the XLink description of what should happen is
> obviated by the fact that SVG describes additional semantics for
> <svg:image>.

So your question is really, whether any random combination of XLink
attributes can be used to override the semantics of any other element.

I asked this on the XLink public list:
  http://lists.w3.org/Archives/Public/www-xml-linking-comments/2006JanMar/0113.html
(using your example, in fact)

and got this response
  http://lists.w3.org/Archives/Public/www-xml-linking-comments/2006AprJun/0000.html

so, basically, SVG describes what happens when allowed values for a
particular element are used, consistent with the semantics of that
element. By using non-allowed values, you are making a new language so
its up to you to say how that language works. Redefining the semantics
of existing elements seems like poor design, so you would be better
using elements in a different namespace.



-- 
 Chris Lilley                    mailto:chris@w3.org
 Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG
Received on Tuesday, 4 April 2006 10:37:31 GMT

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