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Re: [SVGMobile12] Comments: Extensibility

From: Chris Lilley <chris@w3.org>
Date: Sat, 12 Nov 2005 02:43:22 +0100
Message-ID: <65621179.20051112024322@w3.org>
To: www-svg@w3.org
Cc: T Rowley <tor@cs.brown.edu>

Hello www-svg,

> 9.2
> Specification doesn't say how <foreignObject> is supposed to interact 
> with the rendering model.

We agree that this was not necessarily obvious. We have added wording
(see below) to clarify this.

> For example, if XHTML is the content in question, how should things
> like fixed objects and z-layering interact with the SVG rendering and
> other namespaced content in the document?

XHTML, fixed objects and z-order work the same way they normally do; but
the foreignObject establishes a new CSS viewport and thus a new stacking
context. You won't get interleaving between parts of the XHTML and parts
of the SVG, for example.

> 19.4 - "Ultimately, it is expected ... subject to SVG transformations 
> and compositing.  At this time, such a capability is not a requirement."
> Firstly, this paragraph shouldn't be in the "An Example" subsection.

Agreed; we have now shifted it.

> Secondly, not requiring this capability is an interoperability mess.

Not so (but we think you misunderstand which part is optional, and have
clarified it). Its the embedding of, say, XHTML with CSS, or XSL FO, or
X3D, or whatever other foreign markup, that is the optional part. As it
should be for an extensibility point.

You picked upon the parenthetical mention of compositing the rendered
result, and thought that was optional too. We have clarified the text
here as well.

> Graphical elements in the SVG content tree should be required to 
> participate in the SVG rendering model (transformations, compositing).

Yes - and they are.

Here is the current text:

   <h3 id="ForeignObjectElement">The <span
   class="element-name">'foreignObject'</span> element</h3>

   <p>The <span class="element-name">'foreignObject'</span> element is
   an extensibility point which allows user agents to offer graphical
   rendering features beyond those which are defined within this
   specification. </p>
   <p>A conformant SVG user agent is not required to support any
   particular foreign namespace content within 'foreignObject' itself
   nor is it required to invoke other user agents to handle particular
   embedded foreign object types. Ultimately, it is expected that
   commercial Web browsers will support the ability for SVG to embed
   content from other XML grammars which use CSS or XSL to format their
   content, with the resulting CSS- or XSL-formatted content then
   subject to SVG transformations and compositing. At this time, such a
   capability is not a requirement. The CDF Working Group is expected to
   provide this functionality.</p>
   <p>However, the rendered content of a foreignObject must be treated
   as atomic from the point of view of SVG compositing and
   transformation, as if it was a single replaced element.</p>

Please let us know shortly if this does not resolve your comment.

 Chris Lilley                    mailto:chris@w3.org
 Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG
Received on Saturday, 12 November 2005 01:43:31 UTC

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