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@role in SVG

From: Doug Schepers <schepers@w3.org>
Date: Tue, 09 Oct 2007 20:59:43 -0400
Message-ID: <470C23FF.6010108@w3.org>
To: www-svg <www-svg@w3.org>, public-xhtml2@w3.org, Simon Pieters <simonp@opera.com>, aleventh@us.ibm.com, Dave Raggett <dsr@w3.org>, public-cdf@w3.org

Hi, SVG community-

The SVG WG likes the functionality and extensibility that the 'role 
attribute affords, and the potential for increased accessibility, so we 
do want to include it in SVG (and to see it implemented as soon as 
possible, so authors can use it right away).  We've talked about how 
best to do so, and we'd like to solicit opinions from interested 
parties, including the other Working Groups involved, implementors, and 
authors.

To summarize the options, we can include the 'role' attribute in the 
XHTML namespace, or as a native null-namespace attribute.  Each approach 
has benefits and problems.

1) XHTML Namespace
<svg
   xmlns="http://www.w3.org/2000/svg"
   xmlns:xlink="http://www.w3.org/1999/xlink"
   xmlns:xhtml="http://www.w3.org/1999/xhtml"
   xmlns:aaa="http://www.w3.org/2005/07/aaa">
   <g xhtml:role="checkbox" aaa:checked="true">...</g>
</svg>

Pros:
* does not require any changes to SVG syntax... automatically available 
via XML's innate extensibility mechanism
* conforms to current version of the Role spec [1]

Cons:
* is slightly harder to author (requires working knowledge of 
namespaces, or good voodoo skills)
* differs in syntax from how it would work in XHTML and HTML5 (so may be 
harder to learn, and possibly to implement)
* more verbose


2) Native Non-Namespaced Attribute
<svg
   xmlns="http://www.w3.org/2000/svg"
   xmlns:xlink="http://www.w3.org/1999/xlink"
   xmlns:aaa="http://www.w3.org/2005/07/aaa">
   <g role="checkbox" aaa:checked="true">...</g>
</svg>


Pros:
* more similar in syntax to XHTML and HTML5 (easier to use and maybe 
implement)
* less verbose
* maybe less error-prone for authoring, mash-ups, compound documents

Cons:
* would require a change to SVG (see details below)
* would require change to Role spec to allow "host language" (SVG) to 
incorporate it into its own language (note that there is precedent for 
this in the previous version of the Role spec [2], not sure why it was 
changed)

Neutral:
* still requires knowledge of namespaces, but only for including ARIA


Changes Required to SVG Specifications

As mentioned, including 'role' via the XHTML namespace requires no 
changes to SVG (though would benefit from a Note on the details), but I 
understand that some might not find it the cleanest or most 
author-friendly solution.  So, the SVG WG is open to include it directly 
in the SVG language, if that's the solution the community feels is best 
(and if it is allowed by the Role spec).

If we are to include it in the language, just how we do so depends on 
which version of SVG.  We can't add it as a feature to SVG 1.1 or before 
(adding features that change conformance to a past version is not 
allowed in the W3C Process), but we could do so for SVG 1.2 Full with 
few or no problems.  There is a chance we could do it for SVG 1.2 Tiny, 
because it's not yet in PR, but adding features at this late stage might 
not sit well with the standards community (though the implementors on 
the WG assure us that merely adding an attribute is trivial).  We would 
like to do it, but not if it's seen as unacceptable by the standards 
community.

Another factor is that we don't want to be dependent upon the Role 
Attribute  and the CURIE specs for our Rec-Track exit criteria.  But 
neither do we want to specify it separately (or differently) than that 
spec.  A possible solution is that, for SVG 1.2 Tiny, we would include 
it as an attribute whose value is a space-separated list of strings, and 
when the Role and CURIE specs are more mature, in the SVG 1.2 Full 
timeframe, we would change the specification of 'role' to refer to those 
specs.  This is not a very clean solution, but it would get the 'role' 
attribute out there, and let authors create content now in as easy a 
manner as possible.


Changes Required to Role Attribute Specification

As mentioned before, for this to happen, the Role Attribute spec would 
need to explicitly allow SVG to do it.  We'd like feedback from the 
XHTML2 WG on this.  It would be ideal, perhaps, if the Role spec 
optionally allowed the values to be strings instead of CURIEs (as 
specified in a host language), but that may be a bridge too far.


Prompt feedback on this issue would be greatly appreciated.


[1] http://www.w3.org/TR/xhtml-role/
[2] http://www.w3.org/TR/2006/WD-xhtml-role-20060725/#docconf

Regards-
-Doug Schepers
W3C Staff Contact, SVG, CDF, and WebAPI
Received on Wednesday, 10 October 2007 00:59:58 GMT

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