<http://schema.org/description>
"\r\n\r\nTwitter will soon be rolling out 'Annotations,' which will allow developers to add metadata to any tweet that they want.\r\n\r\nTwitter asked itself what type of metadata it could add ..."^^<http://www.w3.org/2001/XMLSchema#string>
<http://thenextweb.com/socialmedia/2010/04/14/twitter-announces-annotations-add-metadata-tweet-starting-quarter-2/>