Threw to top level when I made an error in an expression.

It should wrap this as a diagnostic object, and of course give me the context of the object in the schema whose expression contains the error.

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Boolean

Note that the error was that I wrote "

{ if (../tns:x eq 0) then true else false }

" – see the error. There's no true or false in Xpath. You have to write true() and false().