http://www.rfc-editor.org/rfc/rfc1872.txt
RFC 1872: The MIME Multipart/Related Content-type, E. Levinson1995-12-01T23:00:00-00:00The Multipart/Related content-type provides a common mechanism for representing objects that are aggregates of related MIME body parts. This document defines the Multipart/Related content-type and provides examples of its use. This memo defines an Experimental Protocol for the Internet community.