Re: xmlns in HTML5 (was: Telecon Agenda- Thursday 1500 UTC)

On Fri, 17 Jul 2009 13:23:02 +0200, Ian Hickson <ian@hixie.ch> wrote:

> On Fri, 17 Jul 2009, Steven Pemberton wrote:
>> On Fri, 17 Jul 2009 00:29:42 +0200, Ian Hickson <ian@hixie.ch> wrote:
>> > On Thu, 16 Jul 2009, Steven Pemberton wrote:
>> > > On Thu, 16 Jul 2009 10:50:52 +0200, Toby Inkster <tai@g5n.co.uk>  
>> wrote:
>> > > >
>> > > > For the same reason, xmlns:foo attributes aren't allowed in HTML4
>> > > > either.
>> > >
>> > > Actually, to allow for future changes, the spec says: [...]
>> >
>> > So the following is valid HTML4?
>>
>> Not valid, but permitted.
>
> Woah. What's the difference between "valid" and "permitted"? Aren't they
> both synonyms of "conforming"?

Not at all. Valid has a very well defined meaning, with respect to  
schemata. I used 'permitted' in its English sense. A document with extra  
attributes may be a valid according to some other schema, but it is still  
permitted to send it to an HTML4 processor, because the spec says so.

>
>
>> > > "If a user agent encounters an attribute it does not recognize, it
>> > > should ignore the entire attribute specification (i.e., the
>> > > attribute and its value)."
>> > > http://www.w3.org/TR/html401/appendix/notes.html#notes-invalid-docs
>> > >
>> > > In other words, it should act as if it weren't there. So it is
>> > > allowed, but no meaning is defined.
>> >
>> > (I disagree with your interpretation of that text, by the way; it is a
>> > statement about user agents, not a statement about the conformance of
>> > HTML documents themselves. Requirements on user agents are not the
>> > same as requirements on documents.)
>>
>> I agree entirely. In fact one of my main problems with the HTML5 spec is
>> that it seems to conflate the two, but considering your statement above,
>> the problem must just be that it entwines the two.
>
> Requirements in HTML5 are organised by topic, not by conformance class,  
> if
> that's what you mean, yes. This is generally speaking a pretty common way
> of writing specs at the W3C (e.g. it's what CSS, SVG, and XML all do).
>
> (If you have any feedback on the HTML5 spec, please send it to
> public-html; any feedback would be very welcome.)
>
>
>> But the HTML4 spec defines a document type, and says the processor for
>> that document type must accept certain deviations from that in order to
>> allow for future change. In other words the spec anticipated that other
>> document types would be sent in the future.
>
> Sure, future compatibility is a pretty standard part of any language. But
> if you agree that the above quote is a statement about _user agents_, as
> opposed to authors, I don't understand how you then conclude that it can
> in any way affect document conformance (what authors are permitted to  
> do).

Suppose we define a new markup language, Accessible HTML, which includes  
the role attribute and all the WAI ARIA attributes. It permits an author  
to write a document that validates according to that new schema, and send  
it to an HTML4 processor, with well-defined processing.
The author can also send it to an Accessible HTML processor, which can do  
extra things with it, but it will still work with a legacy processor.

Best wishes,

Steven

Received on Friday, 17 July 2009 12:13:25 UTC