Actually I didn't fully quote one of Philip's emails, so am replicating
his email here (again with his permission):
Shelley Powers wrote:
[...]
PS I will say one thing, and I'm parroting Henri in this regard, to me
a conforming implementation of RDFa in HTML5 is not necessarily one
that only meets what's required for HTML5 -- it has to meet a
conformance requirement for RDF, too.How would we know if the document
is conforming? Because the same annotation in a document served up as
XHTML5, should generate the exact same RDF graph, as would be
generated if the document is served up as HTML5. To ensure this, how
the annotation is interpreted from a data perspective must be defined
in a single document, such as RDFa-in-XHTML.
That's something I'd definitely agree with. E.g. when someone implements
an RDFa parser with JS in a web browser, they should use the same code
to extract data regardless of whether the document was originally
text/html or application/xhtml+xml, and get the same output. That means
there needs to be just one specification saying how to extract data, to
avoid the conflicts you mention.
[...]
The reason why Shane's document is "sparse" on parsing (processing)
information (according to the WhatWG IRC entries) is that Shane was
deferring the RDFa processor conformance to the RDFa-XHTML syntax and
processing document. This was right and proper. He was using good
technique.
The problem in that document is it doesn't define how to map from the
syntax onto the RDFa-in-XHTML processing model, which leaves a gap where
the behaviour is undefined. E.g. I can write <div xmlns:="..."> in HTML,
and I don't know whether that attribute should be ignored or should
redefine the default prefix mapping, because it's impossible in XHTML
and so the RDFa-in-XHTML specification doesn't explain how to handle it.
One idea for fixing the gap is to produce a more detailed mapping from
text/html onto the RDFa-in-XHTML processing model. But that seems like
an unpleasantly difficult solution, since RDFa-in-XHTML wasn't really
designed to be used like that and there lots of small mismatches and
edge cases that make it tricky.
Since HTML 5 already defines how to handle text/html and
application/xhtml+xml in a common processing model, I think redefining
the RDFa processing model on top of the HTML 5 processing model is
possibly the best way to get well-defined, consistent behaviour between
HTML and XHTML. So it would entirely replace the current RDFa-in-XHTML
spec, ensuring there's only a single document telling people how to
parse RDFa in both HTML and XHTML. Maybe it should be thought of as a
new edition of the existing spec, rather than a totally new spec.
I guess there are lots of political/process issues with doing that, but
it'd be nice to have a technically sound solution before getting blocked
by those issues.
--
Philip Taylor
