<http://schema.org/topics>
"Bookmarks Lists,digg,Google,street view,Lists,Mashable,MySpace,Social Network Lists,social networks,Startups,YouTube"^^<http://www.w3.org/2001/XMLSchema#string>
<http://mashable.com/2008/06/16/mashable-digg-50-most-popular/?WT.mc_id=en_bookmarks-lists>