[RFC-2046]
        Freed, N., and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part Two: Media Types", RFC 2046,
        Innosoft, First Virtual Holdings, November 1996.

   [RFC-2047]
        Moore, K., "Multipurpose Internet Mail Extensions (MIME)
        Part Three: Representation of Non-ASCII Text in Internet
        Message Headers", RFC 2047, University of
        Tennessee, November 1996.

   [RFC-2048]
        Freed, N., Klensin, J., and J. Postel, "Multipurpose
        Internet Mail Extensions (MIME) Part Four: MIME
        Registration Procedures", RFC 2048, Innosoft, MCI,
        ISI, November 1996.

   [RFC-2049]
        Freed, N. and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part Five: Conformance Criteria and
        Examples", RFC 2049 (this document), Innosoft, First
        Virtual Holdings, November 1996.

   [US-ASCII]
        Coded Character Set -- 7-Bit American Standard Code for
        Information Interchange, ANSI X3.4-1986.

   [X400]
        Schicker, Pietro, "Message Handling Systems, X.400",
        Message Handling Systems and Distributed Applications, E.
        Stefferud, O-j. Jacobsen, and P. Schicker, eds., North-
        Holland, 1989, pp. 3-41.