Actually, I think Jay Weber is closest to the truth. We added
`multipart/mixed' to handle problems of compound document markup,
without really being conscious of it, and then didn't think hard enough
about the problem.
I beg to differ. multipart started out as a means of stuffing more than one
thing into a message -- that is all it was in the beginning. The /mixed part
fell out of the decision to create multipart/parallel; we needed a name for the
what remained after the cases requiring special interpretation were dealt with.
I don't recall any intention to deal with compound document markup via this
mechanism. Compound documents are great and useful things, but they simply do
not subsume all of the uses of multipart/mixed. For one thing, many messaging
applications have no relationship at all to any sort of document.
Multipart/mixed is missing a specification of just *how* the different parts
go
together (that is, is this picture embedded in that text, or what?), because
that would be straying into the realm of document formats.
I happen to agree that this sort of thing really belongs to compound documents
and not to general messaging, which is why I said that details like "what side
of the screen should this be on" might not be appropriate presentation
attributes for MIME to carry around. Compound documents are more tightly
focused and as a result they have access to techniques and facilities not
present in our more general messaging model.
On the other hand, there's nothing to stop someone from coming along and using
MIME to build some kind of reasonably complete compound document facility.
Regardless of whehter or not you or I think this is appropriate usage, it is
both legal and doable.
Multipart/parallel (meaning simply ``here're a bunch of parts'') and
multipart/alternative seem to have reasonable semantics, though.
I agree. If tightening up the semanatics of multipart/mixed to say that the
parts contained inside are simply a collection of independent things to be
handled in whatever fahsion is appropriate, then I'm all for making such a
change.
Ned