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Re: [SVGMobile12] Interaction with XLink

From: Erik Dahlström <ed@opera.com>
Date: Thu, 08 Jun 2006 17:47:37 +0200
To: www-svg@w3.org
Message-ID: <op.tat3hny9gqiacl@gnorps.palace.opera.no>

Ian wrote:

> On Fri, 27 Jan 2006, Charles McCathieNevile wrote:
> >> > it is unclear what XLink-aware user agents should do when facedwith 
> > > SVG Tiny 1.2 content that explicitly sets the XLink> >  
> attributes,especially now that no DTD is used and therefore the XLink> >  
> attributesdon't normally have their correct values.
> >> Where the attributes are explicitly set (by which I mean are present  
> in> the source of the SVG content in question), they should be  
> interpreted> as per the Xlink specification (see also your other  
> question, below).
>This seems to contradict the SVG specification, which implies that, e.g., 
> the following:
>   <svg xmlns="http://www.w3.org/2000/svg" 
>         xmlns:xlink="http://www.w3.org/1999/xlink">
>      <a xlink:href="test" xlink:show="embed" xlink:type="simple">
>        <rect width="100%" height="100%"/>
>      </a>
>    </svg>
>...should render a black rectangle that is a link, whereas per XLink that 
> link should render the file "test" in place of the black rectangle.
>Please clarify the SVG specification to state exactly how XLink  
> attributeswith unexpected values are to be handled in an SVG context.

The WG considers the spec to be clear enough, for unsupported values the  
spec tells you how to handle them in the given context. Your example uses  
xlink:show="embed" which the SVGT12 spec tells you is not supported on the  
<svg:a> element so it should be treated as an unsupported value.

> > If you meant to ask about when they are set *implicitly* (i.e.>  
> attributes for which default values are defined in the SVG specification 
> > are not present in the source of the content), for an SVG user agent>  
> which implements Xlink, it should supply the default values as specified 
> > by SVG, and for a user agent which implements Xlink but not SVG it>  
> should follow the behaviour specified by the Xlink specification.
>I do not understand why SVG is changing XLink semantics. The XLink 
> specification doesn't seem to allow for attributes to be implied by 
> mechanisms other than DTDs.

Reading XLink 1.1 section 4.3, "Attribute Value Defaulting" it seems that  
other schema are also allowed to change the default values. We have  
checked this with the XML Core WG who told us this was correct.

> In particular, per XLink, this should not create a link:
>   <svg xmlns="http://www.w3.org/2000/svg" 
>         xmlns:xlink="http://www.w3.org/1999/xlink">
>      <a xlink:href="test">
>        <rect width="100%" height="100%"/>
>      </a>
>    </svg>
>Please clarify the SVG specification to state exactly how XLink semantics 
> are being changed.
> > > Please clearly define, for all SVG elements, how XLink attributes  
> must> > be treated when they do not have their expected values.

Again, the WG considers the spec to be clear enough, the SVG Relax NG  
schema does define the default values of xlink-attributes. The SVGT12 spec  
also says what attribute values are supported in the given context.

Please let us know shortly if this does not address your concern.
Thank you
/Erik, on behalf of the SVG WG

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Received on Thursday, 8 June 2006 15:47:59 UTC

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