RFC 1872 (rfc1872) - Page 3 of 8

The MIME Multipart/Related Content-type

RFC 1872                   Multipart/Related               December 1995


   represented within a MIME message using content-IDs or the value of
   some other "Content-" header.

3.1.  The Type Parameter

   The type parameter must be specified and its value is the MIME media
   type of the root body part.  It permits a MIME user agent to
   determine the content-type without reference to the enclosed body
   part.  If the value of the type parameter and the root body part's
   content-type differ then the User Agent's behavior is undefined.

   Note: Constraining the "type" parameter's value to an existing media
   type allows the appropriate processing to be identified without
   creating yet another hierarchy of registered types.  A possible
   default action would have the MIME mail User Agent (MUA) to display
   the "start" entity alone when it could process the media type as a
   basic type but not as Multipart/Related.

3.2.  The Start Parameter

   The start parameter, if given, is the content-ID of the compound
   object's root.  If not present the root is the first body part in the
   Multipart/Related entity.  The root is the element the application
   processes first.

   In the case of a Multipart/Alternative body part containing several
   entities with identical content-IDs the start entity should be
   selected using the Multipart/Alternative rules.

   Note: The "start" parameter allows for types in which the root
   element gets generated by the sending application, perhaps on the
   fly.  Such an application can create the "start" content-id when
   processing begins and then insert the body part when it is complete.

3.3.  The Start-Info Parameter

   Additional information can be provided to an application by the
   start-info parameter.  It contains either a string or points, via a
   content-ID, to another MIME entity in the message.  A typical use
   might be to provide additional command line parameters or a MIME
   entity giving auxiliary information for processing the compound
   object.

   Applications that use Multipart/Related must specify the
   interpretation of start-info.  User Agents shall provide the
   parameter's value to the processing application.  Processes can
   distinguish a start-info reference from a token or quoted-string by
   examining the first non-white-space character, "