View source for RDFa Plugin for WordPress

{{Challenge
|related_to=Web Services, RDFa, 
|challenge_type=Developer
|tags=gsoc, web,
|is_complete=No
}}
An RDFa plugin for WordPress has [http://wordpress.org/extend/ideas/topic.php?id=2134 been suggested] and we think it's a great idea.  It meshes well with the work we've been doing with embedded structured data and adds value to an already great blogging platform.

A successful implementation would:

* Add a button to the WordPress editor toolbar
* Handle a few predefined ontologies, allowing people to easily insert appropriate markup for [http://dublincore.org/documents/dcmi-terms/ Dublin Core] and [http://xmlns.com/foaf/spec/ FOAF] properties
* Support an "advanced" mode for specifying the predicate by URI

Bonus points for consuming RDF Schema files and adding a reasonable UI to the "basic" mode.