RFC 4289:Multipurpose Internet Mail Extensions (MI...
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1. Introduction


   Recent Internet protocols have been carefully designed to be easily
   extensible in certain areas.  In particular, MIME [RFC2045] is an
   open-ended framework and can accommodate additional object types,
   charsets, and access methods without any changes to the basic
   protocol.  A registration process is needed, however, to ensure that
   the set of such values is developed in an orderly, well-specified,
   and public manner.

   This document defines registration procedures that use the Internet
   Assigned Numbers Authority (IANA) as a central registry for these
   values.

   Note:

      Registration of media types and charsets for use in MIME are
      specified in separate documents [RFC4288] [RFC2278] and are not
      addressed here.


1.1. Conventions Used in This Document


   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].



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