If no datatype is specified for @datatime

http://www.w3.org/TR/rdfa-in-html/#additional-rdfa-processing-rules

"If no datatype is specified, and the value does not match any of the
automatically detected xsd datatypes, a plain literal must be generated
with the associated language of the node, if available. "

Could we be more precise regarding datatype here, and use "datatype
attribute" instead of datatype. I'm particularly interested in the case
where there is an empty datatype attribute with @datetime.

-- 
Steph.