Media type versioning (was: Re: Scripting Media Types)

[Larry Masinter]

> I would like to hear what other ietf-types participants think about
> this. 

My opinion is that content negotiation for versioning capability
using MIME type parameters is unworkable.  The use of the MIME
type is to describe the payload sufficiently so that you know
HOW to process it, but the content-type label cannot (and thus
should not) be extended in an attempt to use it to determine
WHETHER a given processor knows enough to be able to process it.

So whether version information should or should not be in
a media type parameter depends pretty much on whether there
is an embedded, easy-to-find version indicator in the data
itself; if there isn't, and processors need to know the version
to choose between different processing methods, then the
version parameter should be mandatory. There is no strong
use case for an optional version parameter, or in general
for duplicating, in MIME parameters, information that is
readily obtained from the content itself.

If you want to do content negotiation, then consider
using media features and media feature negotiation; with
media features you can negotiate not only version information,
but other parameters that might also be necessary to know
in order to determine interpretability, e.g., availability
of compression modes, codecs, fonts, color capabilities,
buffer size limitations, etc.

Larry
-- 
http://larry.masinter.net