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

[ned.freed at mrochek.com]

> Summary:
> o media content might contain version information, but reliance
>   on that can result in wasted resources
> o negotiation via content-features may be a viable mechanism
>   where negotiation is possible, but it is not always
>   possible (and some means of indicating version must be
>   available to the content negotiation mechanism)
> o proliferation of type/subtypes tags for the sole purpose
>   of versioning is undesirable
> that leaves parameters associated with the media type as an
> efficient mechanism for indicating version information.

I would also add that how version information should be handled very much
depends on how the versioning is done. Versioning schemes range from single
integer affairs (V1,V2,V3) to major/minor/patch m.n.o schemes to
feature-by-feature enumerations. Some formats (e.g., PostScript) even allow
conditionalization of features that may not be supported, so documents work
everywhere but work "better" (in some sense) when certain extensions are
present.

IMO the more complex a versioning scheme is the less amemable it is to being
captured in a set of parameters. Once things pass a certain point content
negotiation needs to be used, or if it cannot be used there's no choice but to
rely on information embedded in the data.

				Ned