Last year Crossref and DataCite announced support for HTTP content negotiation for DOI names. Today, we are pleased to report further collaboration on the topic. We think it is very important that the two largest DOI Registration Agencies work together in order to provide metadata services to DOI names.
The current implementation is documented in detail at http://citation.crosscite.org/
The documentation explains HTTP content negotiation as implemented by both Registration Agencies and provides a list of supported content types.