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Re: SVG and MathML in text/html

From: Doug Schepers <schepers@w3.org>
Date: Sat, 15 Mar 2008 12:28:55 -0400
Message-ID: <47DBF947.4010106@w3.org>
To: HTMLWG Tracking WG <public-html@w3.org>

Hi, Henri-

Henri Sivonen wrote (on 3/15/08 11:01 AM):
> On Mar 15, 2008, at 15:58, Doug Schepers wrote:
>> What happens if I'm using one of these legendary content generation 
>> tools that can't handle quoted values (as has been asserted),
> What tools are those and who has asserted?

I don't know of any such tools, but when the argument of using XML 
parsing rules is mentioned, the assertion is frequently made that not 
all content generation tools can follow XML rules.

If you're saying you don't know of any content generation tools that 
cannot generate quoted attribute values consistently, then that means 
there's no known block in requiring quotes.  So there's really no harm 
in requiring them.

>> Rather than the consistent and easy step of always quoting attribute 
>> values, the user now has to think about something that would normally 
>> be automatic.  Maybe it's just me, but that seems harder, especially 
>> to debug.
> If the author doesn't want to think about that, it is always OK to quote 
> values.

You're assuming a single-author system, which is not always the case. 
Giving the option of using unquoted attribute values will mean that some 
people will use it and others won't.  Given mashups, this is likely to 
cause some collisions.

>> My first suggestion is that a UA simply hands the SVG snippet off to 
>> an XML parser.  If that's unpalatable, my alternate suggestion is that 
>> if an SVG element uses unquoted attribute values, the parser ignores 
>> that attribute
> How do you know where that attribute ends without parsing rules like the 
> ones HTML 5 already has?

You've already conceded that we need to close elements in SVG. 
Encountering the string "/>" (or ">" and a subsequent "</...>" for open 
elements) should do it, no?

>> and any subsequent attributes (quoted or not) and proceeds on to the 
>> end of the element, then continues parsing the next element normally.
> How is that more useful that following HTML 5 attribute tokenization as 
> currently drafted?

Because it preserves compatibility with all other SVG content and UAs, 
thus capitalizing on the network effect.

>> So, with the following snippet:
>> <svg xmlns="http://www.w3.org/2000/svg">
>> <circle cx="100" cy="50" r="25" fill=red stroke="blue" />
>> <circle cx="100" cy="50" r="15" fill="yellow" stroke="blue" />
>> </svg>
>> You would see a yellow circle with a blue stroke on top of a black 
>> circle with no stroke.  That's well defined, and not particularly 
>> draconian.  And it's easy to understand.
> How is that more useful that having the first circle filled red and 
> stroked blue?

See above.

> How is that worth the complexity of having two different attribute 
> tokenization rules that get toggled in mid-parse?

See above.  Also, you've already conceded that SVG and MathML need 
particular parsing rules (thus requiring some sort of "SVG/MathML 
parsing mode"), this is simply one more aspect of that, and not a 
onerous one, because the parser already knows how to handle quoted 
attributes.  It puts little to no additional burden on implementations.

I honestly don't understand why the pragmatics of legacy support are 
being disregarded for the sake of ideological consistency that has no 
proven benefit to authors.  What about the design principles of "Degrade 
Gracefully", "Do not Reinvent the Wheel", "Pave the Cowpaths", 
"Evolution Not Revolution", "Avoid Needless Complexity", and "Solve Real 
Problems"?  What true benefit does this confer?  I have been very active 
in the SVG community for 8 years, and while some people have complained 
about namespaces, I have never heard a complaint about having to quote 
attribute values.  Can you supply a single piece of evidence that this 
is a problem?  After all, according to the "Priority of Constituencies", 
we need to be more concerned with users over authors over implementors 
over specifiers over theoretical purity.  This is sounding very much 
like an issue of theoretical purity within the HTML5 spec.

There are far more important and interesting problems to solve with SVG 
in text/html.  The SVG bikeshed already uses the painter's model, it 
doesn't need another coat.

-Doug Schepers
W3C Team Contact, SVG, CDF, and WebAPI
Received on Saturday, 15 March 2008 16:29:28 UTC

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