[whatwg] Micro-data/Microformats/RDFa Interoperability Requirement

Ian Hickson ian at hixie.ch
Tue May 5 21:32:36 PDT 2009

On Tue, 5 May 2009, Manu Sporny wrote:
> There should be a requirement, as Microformats and XHTML1.1+RDFa have 
> required, that a potential solution to this issue should be compatible 
> with both the Microformats and RDFa approaches. This would mean, at a 
> high-level:
> - Not creating ambiguous cases for parser writers.

Noted, thanks.

> - Not triggering output in a Microformats/RDFa parser as a side-effect
>   of WHATWG micro-data markup.
> - Not creating an environment where WHATWG micro-data markup breaks or
>   eliminates Microformats/RDFa markup.

This isn't possible. Even a regular HTML5 document with no microdata 
annotations that links in a style sheet ends up triggering output in 
Microformats and RDFa parsers -- Microformats because any use of 'class' 
can clash with a Microformats class name, and RDFa because any use of the 
"rel" attribute can do the same.

So I'm not sure really how to handle such a requirement.

It's also not clear to me what RDFa's position in text/html is. As I 
understand it, RDFa only applies to XHTML. Thus it seems that HTML5 has 
already broken compatibility with RDFa, since it requires processors to 
handle text/html content in a non-XML manner.

Similarly, the rules for handling CURIEs in RDFa, especially in rel="", 
are already incompatible with HTML4 and HTML5 rules. For example, the way 
that "n:next" and "next" can end up being equivalent in RDFa processors 
despite being different per HTML rules (assuming an "n" namespace is 
appropriately declared).

I don't think there's much that can be done about this (this isn't 
something that we can change HTML5 rules for; browser vendors would not 
accept having to resolve QNames in rel="" attributes as part of 
processing, for one).

> I think these are implied since HTML5 has gone to great lengths to
> provide backward compatibility.

Backwards compatibility in HTML5 is primarily concerned with being 
compatible with legacy markup, of which there is very little when it comes 
to either RDFa or Microformats (especially RDFa, since there's so little 
XHTML content for it to be found in).

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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