[whatwg] Spec should give guidance on compound document integration points

[Henri Sivonen]

The spec mentions the use of XHTML5 elements inside other XML-based  
document formats. However, the use of foreign namespaces inside  
XHTML5 is not covered.

The obvious candidates for compound document mixing are SVG and  
MathML. Also, there are indications that people will want to embed  
RDF metadata in documents even though the syntax of RDF is designed  
for external metadata and isn't really all that good for embedded  
metadata. I think WA 1.0 should give some guidance on these matters.

Where should the svg element from the SVG namespace be allowed in an  
XHTML5 host document? (My expectation: It should be allowed at least  
everywhere where the img element would be allowed. There may be good  
arguments for allowing svg as block as well.)

Where should the math element from the MathML namespace be allowed in  
an XHTML5 host document? (My expectation: It should be allowed where  
strictly inline level content is allowed. My understanding is that  
also display math has inline semantics even though it has a blockish  
presentation.)

Where should the RDF element from the RDF namespace be allowed in an  
XHTML5 host document? (My expectation: It should be allowed as a  
child of the head element. Other metadata goes there and the contents  
of head are hidden in legacy browsers, so the text node descendants  
of the RDF element from the RDF namespace won't leak to presentation  
in legacy browsers. Also, if conformance checkers don't have a hole  
that allows embedded RDF, people who want to embed RDF will come up  
with worse workarounds to avoid eliciting errors in conformance  
checking. To work around the fact that RDF envelope is designed for  
external metadata and not embedded metadata, XHTML5 should probably  
suggest that authors use rdf:about="" to refer to the current  
document as per XMP*.)

And then something more controversial:
Should an XHTML5 conformance checker allow arbitrary foreign elements  
as children of the head element in order to allow free  
experimentation with invisible non-RDF metadata in a way that doesn't  
encourage experimenters to put their stuff inside comments or  
something equally ugly?

* http://partners.adobe.com/public/developer/en/xmp/sdk/ 
XMPspecification.pdf page 23

-- 
Henri Sivonen
hsivonen at iki.fi
http://hsivonen.iki.fi/