Saxon

For XQuery 3.1 try/catch, in comparison to XSLT 3.0 try/catch, there is an extra variable implicitly declared in the scope of the catch clause, namely err:additional.

https://www.w3.org/TR/xquery-31/#id-try-catch says that the value of err:additional is "Implementation-defined. This variable must be bound so that a query can reference it without raising an error. The purpose of this variable is to allow implementations to provide any additional information that might be useful."

But the variable is not bound in Saxon, and so references do raise an error.

There are tests that the other variables (err:line-number, etc.) are defined in QT3 prod/TryCatchExpr, but no tests for err:additional.