http://norman.walsh.name/2005/09/14/xmlid 8 119 2005-09-14T16:56:35-04:00 $Date: 2005-09-14 19:24:32 -0400 (Wed, 14 Sep 2005) $ Norman Walsh 2005 Norman Walsh It's not really news anymore, but xml:id is now a Recommendation. Alas, it's just a little too early to declare victory. The job won't be completely finished until we address XML Canonicalization. A program is only complete when its last user is dead. It's not really news anymore I suppose, but xml:id Version 1.0 is now a Recommendation. Alas, it's just a little too early to declare victory. The job won't be completely finished until we address the problems revealed in Canonical XML (C14N). In case you aren't an XML hack, or you happened not to have noticed the discussion, the problem in brief is this: C14N specifies that when you canonicalize a document subset, “attributes in the xml namespace, such as xml:lang and xml:space” are inherited. That means if you start with a document like this one: <doc> <wrapper xml:space="preserve"> Some content. <nested>More content</nested> </wrapper> </doc> and apply C14N to the element named “nested”, its canonical form is: <nested xml:space="preserve">More content</nested> That works fine for xml:lang and xml:space which have inheritable semantics. It doesn't work at all for xml:id: an ID is associated with a particular element, it does not inherit. Anyway, whether you think xml:id was a bad idea or not is water under the bridge at this point. Critically, for me anyway, is the fact that C14N was already broken before xml:id came along. The xml:base attribute doesn't inherit in the same way as xml:lang and xml:space either and XML Base was already a Recommendation when we started working on xml:id. The open question at this point is, how should C14N be fixed? For xml:id and any other attributes that may be added to the xml namespace in the future, the answer is clear: C14N must not treat them as inheritable. What's less clear to me is what C14N should do with xml:lang, xml:space, and xml:base. I think it breaks down into two cases, each with two possibilities: How should xml:lang and xml:space be handled? They should not be inherited. They should be inherited just as they are now. How should xml:base be handled? It should not be inherited. It should be subjected to “fixup” and then inherited. By fixup, I mean that the correct absolute value should be used, rather than the literal value of the attribute as the current specification indicates. We talked about this a little bit on the XML Core WG telcon today and I think Daniel Veillard convinced me that the right answers are “1b” and “2b”; his argument being the principle of least surprise. What do you think the right answers are?