<http://schema.org/description>
"Google AdSense released Ad Links on June 09, 2005 and publishers had plenty of time to test them out.  A thread at WebmasterWorld named AdLinks bringing most of the revenue? Can anyone confirm? shows "^^<http://www.w3.org/2001/XMLSchema#string>
<https://www.seroundtable.com/archives/002433.html>