<http://schema.org/topics>
"announcements,blogger,digg,Facebook,flickr,friendfeed,Google,Mashable,movabletype,news,picasa,social,Social Media,Twitter,typepad,Vimeo,Web Apps,WordPress,YouTube"^^<http://www.w3.org/2001/XMLSchema#string>
<http://mashable.com/2009/03/04/social-media-comments/>