Saxon

It's not the world's most wonderful message but I think it's correct.

The key is in XSD 1.1 Part 1 §3.13.6.2 rule 2.2.5: {in the static context for evaluation of the XPath expression in an assert), " The in-scope schema definitions are those components that are present in every schema by definition, as defined in Built-in Attribute Declarations (§3.2.7), Built-in Complex Type Definition (§3.4.7) and Built-in Simple Type Definitions (§3.16.7)."

The hidden meaning of that rule is that types defined in the schema itself are not available for use in assertions. The reason for that rule is to prevent circularity: since types in the schema are defined with reference to assertions, then the assertions can't be defined with reference to types.

Thanks for clarification. As a suggestion, maybe you can add an error code to identify the problem and point to the specification.

Not easy, because we simply initialise a static context for evaluating the XPath expression, and then fire off the XPath processor: the XPath processor can't find the type name in its static context, but it has no idea why this particular type is absent.