"Introduction The 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"". RFC 2045 [1] describes mechanisms for specifying and describing the format of Internet Message Bodies via content-type/subtype pairs. We believe that ""model"" defines a fundamental type of content with unique presentational@ hardware@ and processing aspects. Various subtypes of this primary type are immediately anticipated but will be covered under separate documents."
RFC 2077-1997 history
1997RFC 2077-1997 The Model Primary Content Type for Multipurpose Internet Mail Extensions