http://www.rfc-editor.org/rfc/rfc2077.txt
RFC 2077: The Model Primary Content Type for Multipurpose Internet Mail Extensions, S. Nelson, C. Parks, Mitra1997-01-01T23:00:00-00:00The purpose of this memo is to propose an update to Internet RFC 2045 to include a new primary content-type to be known as "model". [STANDARDS-TRACK]