Scripting Media Types

[Bruce Lilly]

On Sat February 12 2005 12:45, ned.freed at mrochek.com wrote:

> The fact that these subtypes of text are in widespread use leads me to suggest
> an alternate approach: Why not register them, but mark them as obsolete with a
> pointer to the type that should be used instead? The registration will then
> serve two purposes: To make it clear what the types contain when they are used
> and to also make it clear they should no longer be used. 

If one looks at the IANA-maintained registry
(http://www.iana.org/assignments/media-types/text/  for the text
types) one sees only a list of subtype tag names with references
to documents.  It's not clear, therefore, how one would go about
marking a subtype as obsolete in a way that would be clear and
obvious to implementers.  Nor is it clear how one would provide a
pointer to a different type in a way that would be clear etc. to
implementers.  Finally, it should be noted that content may be
archived for a considerable time;  how is one to determine whether
or not a type specified in an archived document was valid at the
time that content was created; I see no mechanism for provision
of a timestamp on changes in status of a type or subtype
registration?

> Hinting isn't sufficient IMO. We're trying to provide usage guidance here,
> so the problematic nature of calling this sort of material text should
> discussed.

Right.  And I'm not sure how something as much as mere hinting can
be achieved w.r.t. "obsolete" types with the current registry (lack
of) structure [compared, e.g. to the structure of the charset
registry].  Much less something that provides clear guidance
regarding usage.

About the only thing an implementer can do for non-private-use tags
without extensive manual effort for each type and subtype is to
determine whether something which appears where a media type is
supposed to appear is in fact a registered type -- that's the case
because that's all that can be mechanically determined from the
registry.  Thus a validating parser of Content-Type fields (for
example) can easily indicate that a type is registered -- a table
of registered types can be consulted (though such a table can get
out-of-date quickly) -- but it's much more difficult to be able to
indicate nuances such as whether/when a type has become obsolete,
what other types are related and in what ways, etc.