In section 3.12.4 (CTA) it is stated that "If a dynamic error or a type error is raised during evaluation, then the {test} is treated as if it had evaluated (without error) to false."

This is then glossed in a Note: "Dynamic errors and type errors in the evaluation of {test} expressions cause neither the schema nor the document instance to be invalid."

The reader could be forgiven for missing the significance of the phrase "during evaluation" | "in the evaluation" in these sentences. Neither is intended to apply to type errors that are detected statically. XPath processors are at liberty to detect type errors statically, and such errors should be handled in the same way as syntax errors in the XPath expression - that is, a violation of the constraints on schema documents. It would be easy enough to add to the note the sentence: "However, if type errors are detected statically by the XPath processor, the effect is the same as for other static errors in the XPath expression."

This then raises the question that 3.12.6 states:

"The {expression} property of the XPath Expression is a valid XPath expression, as defined in [XPath 2.0]."

However, XPath 2.0 does not define the term "valid XPath expression". I think that what is intended is "an XPath expression containing no static errors".

The text for assertions in 3.13.6.2 makes the same mistake in referring to "valid XPath expressions."

For evaluation of assertions, I can't find any text equivalent to that in CTA that says dynamic errors cause the assertion to be treated as false. Perhaps I missed it.