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This issue was originally reported by Xan Gregg. Allow a wildcard to indicate that it will allow any element that conforms to a specified type. See http://lists.w3.org/Archives/Public/www-xml-schema-comments/2002JanMar/1137.html See also http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2002Sep/0094.html This item was discussed in the meeting of 2004-05-12 (http://www.w3.org/XML/Group/2004/05/xml-schema-ftf-minutes.html); there was no consensus, the WG being equally divided between the desire to adopt the proposal and the desire to abandon the desideratum. We agreed to postpone further discussion; the topic may come up again. If it proves useful in supporting versioning, there is a higher likelihood of adoption. Proposal: Xan Gregg (member-only link) (http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2002Nov/0150.html) According to the requirements document, this topic was discussed in the past and was postponed for later reconsideration.
This proposal (allowing typed wildcards) is such a large step away from existing validation techniques that I think it's too large a step for a dot release. I'm not sure I understand the use cases properly, and some of the motivating examples I see in discussions strike me as just poor design that should not be encouraged. And as one of the commentators points out, many of the motivating examples could actually be solved with substitution groups. On the other hand, this might be precisely what is needed to solve what might be called the problem of architectural forms. So I propose to close this issue with a resolution of LATER.
On 20 October 2006, the Working Group agreed to close this issue with a resolution of LATER. That is, this may be a good idea (or may not be), and may be considered for later versions of the specification, but it will not be part of XML Schema 1.1. The WG did not adopt a formal rationale; for what it's worth, my understanding of the WG's motivation is that this change would involve rethinking things at a fundamental level and should be done, if at all, only in the context of a deeper-going revision of the spec than is represented by XML Schema 1.1.