The *meaning* of any given language tag would be no more or less a problem under the proposed revision than it was for RFC 3066 or RFC 1766. For instance, there is a concurrent thread that has been discussing when country distinctions are appropriate or recommended ("ca" or "ca-ES"?); this discussion pertains to RFC 3066, and part of the issue is that meanings of tags are implied rather than specified -- and always have been even under RFC 1766 (I pointed this out five years ago when we were working on preparing RFC 3066).
So, for instance, when an author uses "de-CH", what does he intend recipients to understand to be the difference between that and "de-DE" or even "de"? Neither RFC 1766 or RFC 3066 shed any light on this, and ultimately only the author knows for sure.
Under RFC 3066, it was the *exceptional* case that a complete tags was registered, allowing some indication of the meaning of the whole (though even in that regard nothing really required that the documentation provide clear indication of the meaning). The 98% cases were those like "de-CH" in which it was assumed that everyone would understand what the intended meaning is.
This whole question of what 'matches' is subtle. Consider the case when I have a document that has variant content by language (e.g. different sound tracks), and the user indicates a set of preferred languages. If the content has "de-CH" and "fr-CH" (swiss german and french), and a default "en" (english) and the user says he speaks "de-DE" and "fr-FR", on the face of it nothing matches, and I fall back to the catch-all default, which is almost certainly not the best result.
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David Singer
Apple Computer/QuickTime
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