X Accept

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

curl -H "Accept: application/rdf+xml" -L http://richard.cyganiak.de/2008/03/rdfbugs/accept.php

URIs for formats are more specific than MIMEs from W3C.

curl -H "X-Accept: http://www.w3.org/ns/formats/RDF_XML" -L http://richard.cyganiak.de/2008/03/rdfbugs/accept.php

Or, use a less standard URI for the same format:

curl -H "X-Accept: http://provenanceweb.org/format/mime/application/rdf-PLUS-xml -L http://richard.cyganiak.de/2008/03/rdfbugs/accept.php

A bunch of Accept headers in df-epoch.sh