XPath 2.0 implementation

The rules for effective boolean value have changed. These rules make it a type error to ask for the effective boolean value of anything other than a sequence starting with a node, or a singleton boolean, number, or string. For example, testing the effective boolean value of an xs:anyURI value or of a sequence of integers is now an error.

Similarly, it is now an error for the value of a predicate in a filter expression to evaluate to anything other than a sequence starting with a node, or a singleton boolean, number, or string.