Subject: Re: [arch-d] version numbers

From: Mark Baker <[email-masked]>
Date: Wed, 4 Mar 2009 14:47:53 -0500

On Mon, Feb 23, 2009 at 5:26 PM, Ray Denenberg, Library of Congress
<[email-masked]> wrote:
> Studying existing mime type registrations, I cannot find one in which the
> issue of different possible versions of a format is taken into
> consideration.
>
> For example, "application/xhtml+xml" is for xhtml 1.0, according to rfc 3236
> . So how does that apply to xhtml 1.1? Is the statement in the rfc that it's
> for 1.0 just ignored?

It's suitable for more than just 1.0, though only because 1.0 defines
extensibility rules that define what the document means in the
presence of extensions (although the way it does it is a bit of a
mess, i.e. as UA conformance rules instead of defined document
semantics).  This is mentioned in 3236;

     With respect to XHTML Modularization [XHTMLMOD] and the existence
     of XHTML based languages (referred to as XHTML family members)
     that are not XHTML 1.0 conformant languages, it is possible that
     'application/xhtml+xml' may be used to describe some of these
     documents.

>
> Clearly we don't want to be registering a mime type for every new version,
> so wouldn't it be better if the registration is independent of version?

It is, usually.  Consider text/html and the many versions of HTML it
is used with.

> Could the version instead be indicated, for example by a mime parameter?

No.  We get this question over on ietf-types once a year or so, the
most recent edition being this one;

http://www.alvestrand.no/pipermail/ietf-types/2009-February/002152.html

Media types have an implicit versioning story that isn't widely
understood, and also isn't documented, but it's quite straightforward;
the media type name can be thought of as a handle that identifies a
series of compatible languages, where "compatible" means roughly, in
practical terms, that an old piece of software can reasonably process
a new document of that language.  So as long as the language evolves
this way, the old media type can be reused.  If it doesn't, then a new
media type is required.  Of course, we don't see that very often,
because the cost of deploying a new media type is very high.

Mark.

---

From: "Ray Denenberg, Library of Congress" <[email-masked]>
Date: Wed, 4 Mar 2009 14:51:23 -0500

Thanks, Mark.   That clears up my confusion.

--Ray