Re: HTML 4 Profile for RDFa

Philip Taylor wrote:
> ...
> Hmm, maybe a better example of what I intended is:
> 
>   <div xmlns:t="test1:">
>     <div xmlns:T="test2:">
>       <span property="t:x T:y">Test</span>
>     </div>
>   </div>
> 
> which is well-formed XML and has a clear definition in RDFa-in-XHTML, 
> but the defined behaviour is impossible to reproduce in text/html 
> (because xmlns:t and xmlns:T (and XMLNS:T) are parsed identically by an 
> HTML parser and there's no way to distinguish them afterwards).
> 
> RDFa-in-text/html could:
> 
> * Assume attributes are all treated as lowercase (breaking <div 
> xmlns:T="..." property="T:..."> which works in XHTML);
> 
> * Say CURIEs (in both XHTML and HTML) match prefixes case-insensitively 
> (breaking compatibility with current implementations);
> 
> * Change text/html parsing to preserve attribute case (breaking 
> compatibility with current parsers);
> 
> * Use some other prefix-binding mechanism (in both XHTML in HTML) like 
> prefix="t=... T=..." instead of xmlns:t="..." (breaking current 
> implementations and deployed content, but avoiding the mess of parsing 
> differences between XHTML and HTML).
> 
> I can't think of any other solutions, so something is going to break no 
> matter what is chosen.

It's clear that if RDFa is to be used with prefix declarations done with 
xmlns, then mixing uppercase and lowercase declarations is not going to 
work.

I think restricting prefixes to be lower-case (insert proper Unicode 
terminology here) would be acceptable; it's easy to live with, and 
avoids introducing yet another prefix declaration mechanism.

BR, Julian