From: Paul Kyzivat <[EMAIL PROTECTED]>

   IMO there is nothing really special about by-reference, except that it 
   is a disposition-type whose intrinsic processing is "ignore". Hence the 
   only processing that it might receive is determined by a reference, if 
   any. If no reference is found then there is no processing.

That's the case if handling is 'optional'.  But if handling is
'required', then the containing part is un-processable:

   8.4.  The 'by-reference' Disposition Type

   [...]

   [...]  A recipient of a body part whose disposition
   type is 'by-reference' that cannot find any reference to the body
   part (e.g., the reference was in a header field the recipient does
   not support and, thus, did not process) MUST NOT process the body
   part.  Consequently, if the handling of the body part was required,
   the UA needs to report an error.

That convention gives the sender a way to enforce that the processor
can see the reference to the part in question.

   Also, in principle it would be possible for a single body to be 
   processed multiple times, using differing contexts.

Yes, I was sloppy about that.  But I believe that what I wrote handles
that situation implicitly, because in such a case, the stated rules
give two different instances where processing of the part is
specified, and the rules regarding processing context give the proper
context for each instance of processing.

I've also been sloppy about noting that the Content-Disposition
parameters of parts become part of the processing context of all their
subordinate components.

Dale
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