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Unique particle attribution is normative and not optional, but not all
processors check it correctly and some processors check it optionally.
Of course that leads to interoperability errors, and not just around
UPA, but that's the state of the art.
Ian Graham wrote:
> I've been fiddling around with very simple schemas that violate the UPA
> constraint -- and have found that some schema tools flag UPA errors
> (e.g. oXygen), while others (e.g. XML spy) do not. This inconsistency
> is, at best, confusing -- but at worst would seem to lead to
> interoperability problems, since a designer could build a schema with
> one toolset and find it is not acceptable to another.
> So am I missing something here? Is UPA really an inviolable constraint
> [my interpretation], or is it just a guideline, in the manner of
> Appendix E 'Deterministic Content Models (Non-Normative)' in the XML 1.0
> specification? And if it's just a guideline, would this not lead to
> interoperability problems as I've just outlined?
> And, if someone already went down this rat hole, can anyone refer me to
> the corresponding xml-dev (or other) thread ;-)
> Best --