Support for HTML5 datetime and data attributes

Hi,

The way microdata property values are processed in HTML5 depends on what tag
contains the value. For most tags, it's either the text content, or one of
the usual suspects: @content, @src or @href.

There are two tags however in microdata where the property value does not
come from any of the RDFa attributes. These tags are <time> and <object>
where the property value comes from @datetime and @data, respectively. It is
to be expected that HTML5 authors will place relevant values in these
attributes, and I'm wondering how RDFa 1.1 can target these without
resorting to adding a content attribute.

Let's take the example of <time> which in HTML5 can look like this:
<time itemprop="birthday" datetime="2009-05-10">May 10th 2009</time>

Does the @content attribute have to be explicitly added in the RDFa form? Is
there a shorter way to turn that into RDFa than the following one?
<time
property="birthday" datetime="2009-05-10"
content="2009-05-10T00:00:00-00:00" datatype="xsd:dateTime">May
10th 2009</time>

How about the data attribute?

I didn't find any of these attributes in the rdf-core spec, nor in HTML+RDFa
1.1.

Steph.