http://rdfabout.com/sparql?query=DESCRIBE+%3Chttp://www.rdfabout.com/rdf/usgov/
congress/house/99/az%3E

gives in the tabulator extension:
"This XML file does not appear to have any style information associated with it. 
The document tree is shown below."
but why?

$ curl -I "http://rdfabout.com/sparql?query=DESCRIBE+%3Chttp://www.rdfabout.com/
rdf/usgov/congress/people/M000303%3E"
HTTP/1.1 200 OK
Date: Sat, 01 Sep 2007 00:07:10 GMT
Server: Apache/2.2.3 (CentOS)
Content-Length: 4201
Cache-Control: private
Connection: close
Content-Type: application/rdf+xml

Only in the extension.  Other things work in the extension.