Dublin Core/GRDDL

>From the Microformats Wiki ...

"Some rel values have been added to this page perhaps in one of the 
tables above, but no examples, nor an actual specification explicitly 
stating that the value(s) should be used in the HTML4 'rel' attribute 
could be found. They are listed here in the hopes someone can discover 
more specific/precise URLs to examples or specifications about them 
(preferably both).  Until such precise URLs to examples/specs are 
provided, the values can be treated as they are purely theoretical and 
thus of little interest. "

schema.DCTERMS, schema (dot) ...

These are used as links in GRDDL transformations. See:http://www.w3.org/TR/grddl/#sec_dubc_ex If the link is not present, the RDF node will be empty upon transformation.  e.g. name=DCTERMS.title requires rel=schema.DCTERMS for  processing.  The head profile attribute, absent in HTML5 is required also I believe.

So much for mechanical (developer) considerations.  But since header metadata is "hidden" from a viewer who does not know where to look for it, this is a bit scary.

--Gannon