xhtml:about contains the following:
<quote>The RDF statement's subject is specified by the xhtml:property attribute.</quote>
first problem: it's not the subject, it's the predicate
currently, xhtml:property says:
<quote>
The xhtml:property attribute specifies the IRI of the predicate of an RDF statement for in content metadata.
</quote>
the xhtml:property attribute actually contains a list of CURIEs, not just one. this means that there is not just one RDF statement, but potentially several. (the schema-generated datatype for this already says CURIEs)