From: Ned Freed <NED(_at_)SIGURD(_dot_)INNOSOFT(_dot_)COM>
The subtypes of multipart are there to tell your code how to interpret the
contents, just like any other subtype.
The difference between multipart/mixed and multipart/parallel is all
about presentation, not about interpretation. In that it is very
similar to the issue of attachments, and unlike the rest of the
subtypes.
An anecdote might help: I wrote the Servicemail package,
which automatically reads and responds to MIME mail. The mixed vs.
parallel distinction is the *only* part of MIME that has no meaning as
input to my software, simply because there is no presentation of
input messages. (Well, maybe there is a model of presentation to
programs, but it certainly is not temporal.)
So if we want Content-type to be purely about interpretation, and I think
it should be, then we should (1) forget about multipart/attachments,
(2) remove multipart/parallel, (3) remove the "displayed serially"
semantics from multipart/mixed, and (4) figure out another way of
including presentation information. Content-Disposition is a good
idea, maybe Content-Presentation is more intuitive. Here's a new take:
presentation := "Content-Presentation" ":" style
style := "indirect" / "serial" / "parallel"
The semantics would be like this: inside the scope of a multipart/mixed,
all parts marked presentation parallel would be displayed immediately
and simultaneously, followed by parts marked presentation serial in the
order they appear, followed by a simultaneous presentation of pointers
(icons, a list box) for all parts marked indirect. If serial is the
default presentation, then multipart mixed without presentation markers
has the same semantics as now (it won't break current implementations).
The use of a separate header line is nice for software like Servicemail
that doesn't have a presentation model, because it can simply ignore
Content-Presentation.
Jay
--
Jay C. Weber weber(_at_)eitech(_dot_)com
Enterprise Integration Technologies
weber(_at_)cis(_dot_)stanford(_dot_)edu
459 Hamilton Avenue, Suite #100 (415)617-8002
Palo Alto, CA 94301