http://www.rfc-editor.org/rfc/rfc6839.txt
RFC 6839: Additional Media Type Structured Syntax Suffixes, T. Hansen, A. Melnikov2013-01-01T23:00:00-00:00A content media type name sometimes includes partitioned meta- information distinguished by a structured syntax to permit noting an attribute of the media as a suffix to the name. This document defines several structured syntax suffixes for use with media type registrations. In particular, it defines and registers the "+json", "+ber", "+der", "+fastinfoset", "+wbxml" and "+zip" structured syntax suffixes, and provides a media type structured syntax suffix registration form for the "+xml" structured syntax suffix. This document is not an Internet Standards Track specification; it is published for informational purposes.