Empty @typeof

What is the meaning of this?

   <div about="#foo">
     <div typeof="">
       <span property="dc:title">xyzzy</span>
     </div>
   </div>

Is "xyzzy" the title of "#foo" or the title of a BNode created by the  
second <div>?

Step #4 and #5 in the processing sequence say "if @typeof is present"  
then typeof sets a new subject. However, step #6 says of @typeof: "if  
present, the attribute must contain one or more URIs" (i.e. not zero  
or more).

Can an empty typeof set a new subject, or is it invalid and thus  
ignored? It would be nice if the syntax document could be clarified.

Yes, I know it would be helpful if I'd raised this issue before RDFa  
reached PR stage, but I've only just noticed it.

-- 
Toby A Inkster
<mailto:mail@tobyinkster.co.uk>
<http://tobyinkster.co.uk>