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Re: [1.2T-LC] foreignObject content and referenced resource (ISSUE-2062)

From: Anthony Grasso <anthony.grasso@cisra.canon.com.au>
Date: Fri, 17 Oct 2008 12:11:43 +1100
Message-ID: <48F7E64F.6040706@cisra.canon.com.au>
To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>
CC: www-svg@w3.org

Hi Dr. Hoffmann,

The SVG Working Group discussed this issue and as a result made changes to the 
specification. Please see my comments below.

Doug Schepers wrote:
> Hi, Dr. Olaf-
> 
> Thanks for your insightful comment.  I've raised ISSUE-2062 in our
> Tracker, and the SVG WG will discuss it and get back to you as soon as
> possible.
> 
> Thanks-
> -Doug, on behalf of the SVG WG
> 
> 
> Dr. Olaf Hoffmann wrote (on 9/20/08 9:34 AM):
>> Hello SVG WG,
>>
>> doing some experiments with foreignObject I discovered, that there is some
>> information missing in the definition or description of foreignObject.
>> This should be clarified.
>>
>>
>> 1. Compared to SVG1.1 the use of xlink:href is new, but in the attribute 
>> definitions is not mentioned, what should happen with the referenced 
>> resource (what can be almost everything according to 14.1.4 Reference 
>> restrictions), if a user agent decides to interprete foreignObject 
>> somehow.
>>
>> For example for a referenced XHTML document (as well as for
>> embedded XHTML) Opera 9.5 decides to display the top left corner 
>> fragment of the referenced document into the area described by 
>> x, y, width, height attributes following the painters model (earlier 
>> other elements below, later elements on top).
>> Other parts of the referenced document beyond this area are not
>> accessible.
>>
>> My guess is too, that it is at least intended, that the referenced 
>> document or a fragment of it is somehow displayed inside the
>> given area (following the painters model), if displayed at all.
>> But then this should be mentioned in the attribute definition 
>> as for image, use, animate, set etc or in the general 
>> description of the element, as for example for audio and video.
>>
>> Another interpretation could be, that the xlink:href references
>> an alternative view, a description (xhtml:longdesc), something 
>> related to the foreignObject content. Or the content of 
>> foreignObject could be an alternative fallback for the 
>> referenced document similar to the behaviour of xhtml:object. 
>>
>> (Side note: the element animation has a similar problem, it
>> is not mentioned, what the purpose of xlink:href is, however
>> this can be guessed, but I would like to suggest to replace
>> "The referenced SVG document represents a separate document 
>> which generates its own parse tree and document object model."
>> with
>> "The SVG document referenced with the xlink:href attribute 
>> represents a separate document which generates its own 
>> parse tree and document object model."
>> to cover this problem for the animation element, a similar
>> description could solve parts of problem for foreignObject as
>> well).
>>
>>
>> 2. According to the SVG1.1 usage and the example
>> 23_02.svg it is possible too to put the foreign content
>> directly inside the foreignObject.
>> If additionally an external resource is available with
>> xlink:href, what happens? What is the intended 
>> relation between the content and the document
>> referenced by xlink:href? 
>> Is it an arbitrary choice of the viewer, what will be
>> displayed if the viewer decides to display something
>> and we assume that both contents are displayable for
>> the viewer somehow?
>> a) Is the foreignObject content displayed only?
>> b) Is the referenced document displayed only?
>> c) are both content and referenced document displayed?
>> c1) is the content on top (because of the painters model and
>> the xlink:href is slightly earlier in the source code than the 
>> content?)
>> c2) is the referenced document on top?
>> d) should the viewer provide an interface to select, what
>> to display?
>>

An additional paragraph was inserted before the last paragraph in The 
'foreignObject' element section [1].

The 'xlink:href' attribute of 'foreignObject' had a sentence added to the end of 
the paragraph [2].

>> 3. Obviously different from SVG1.1 in SVGT1.2 the
>> foreignObject currently does not create its own
>> viewport
>> http://www.w3.org/TR/SVGMobile12/coords.html#ElementsThatEstablishViewports
>>
>> How is the foreign content aligned relative to the
>> user coordinate system? Is there a chance for the author
>> to influence, which part of the referenced content is
>> displayed, if a viewer like Opera 9.5 displays only a fragment
>> or is this the problem of the foreign language (for example
>> XHTML, typically creating scrollbars or other mechanisms 
>> automatically to get access to the content of the complete 
>> document)?
>> Is the content outside the x, y, width, height area always
>> clipped or is it on the viewer to decide this or on the author
>> to avoid this?
>>
> 
> 

The 'foreignObject' element was added to the list of elements that establish new 
viewports [3].

Please let us know at your earliest convenience if these changes are satisfactory.

Kind Regards,

Anthony Grasso.


[1] http://dev.w3.org/SVG/profiles/1.2T/master/extend.html#ForeignObjectElement
[2] 
http://dev.w3.org/SVG/profiles/1.2T/master/extend.html#ForeignObjectElementHrefAttribute
[3] 
http://dev.w3.org/SVG/profiles/1.2T/master/coords.html#ElementsThatEstablishViewports
Received on Friday, 17 October 2008 01:12:41 GMT

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