<http://schema.org/description>
"A Google Webmaster Help thread has a nice little crawling tidbit for advanced SEOs.  Did you know that it typically takes a long time for a PDF document to be recrawled and indexed by Google?  Exactly"^^<http://www.w3.org/2001/XMLSchema#string>
<https://www.seroundtable.com/archives/022255.html>