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Re: Content Types

1991-08-28 01:54:25
Please review the past messages on this group to find out why there is an
express limit on the number of types.

I had reviewed your objection to the open-ended type/subtype before I sent
out my previous mail.  I undstood your motivation.  Your point of view was
well taken.

The purpose of the type is to give the most general description of what the
contents are.  By intent it is an extremely limited set, so that the complete
set can be itemized in a single document and all implementations everywhere
can be expected to know about all of them.  If anything is to be done to the
set of types, it should be to further reduce their number, not add more.
[Obvious: fold TEXT-PLUS into TEXT, fold IMAGE, AUDIO, VIDEO into BINARY.]

For terminal-based mail reader, "TEXT" class and "BINARY" class are more
important than "type".  But for sophiscated mail reader, the "class" does not
provide enough information.  It is merely a hint.  The real information is
provided by "type."  Before the Altanta WG, Neil and I suggested to split the
original type/subtype into Content-Class and Content-Type.  The primarly
reason of the splitting is for these two types of mail readers.  I don't like
the type/subtype approach because it creates a complexity for user (or vendor)
to choose the proper type for a subtype and requires the uniqueness of
type/subtype combination.  I am afraid that this approach may create
interoperability problem.

The current nine is a result of a lot of compromising on the part of a number
of people, and changing them now (adding or removing) would create show-
stoppers among people who formerly were in agreement.

This expressly excludes POSTSCRIPT, INTERLEAF, and even PEM.

I didn't ask for adding or removing any class.  My original message was
asking for the guideline how to pick the proper type for a subtype, and
reviewing the potential problem with the optional subtype.  My original
question was triggered by the type/subtype confusion appeared to me while
I was implmenting a RFC-XXXX UA.

Why is it, just as we finally crush one resurgence of an old bad idea from a
newcomer, that we get another one???  Conspiracy theorists would have a field

Vincent, I know you didn't realize what you stepped into, but please, for
everyone's sake, review the past 6 months' worth of IETF-822 messages before
you dive in and get lots of people teed off at you.  Thanks!!

I have monitored the IETF-822 and IETF-SMTP messages for the last 6 months.


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