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> XQuery can't guarantee schema validity completely, because it does not
> model all of XML Schema (eg it does not model identity constraints or
> facets), and because there are cases in which the type information used is
> not specific enough. It *can* catch a large number of common errors.
It's hard to see how anything bigger than the toy examples in the use
case document are ever going to have a static type that's more general
than document to document. Real transformations use parent and ancestor
axes, they use constructed element names, they use data pulled in via
document() from a source not known until runtime as it depends on
data in the input document. In any of these cases the static type
system gives no information, and as you combine such functions together
the lack of type information is infectious.
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