Variables and Namespaces
Both variables and namespaces can be defined in two seperate manners. The first is through the use of declarations in the versa query. The second is left to the implementation, but a conforming implementation must allow for defining variables and namespaces in some manner external to the query.
In the case where a variable or namespace definition clashes between that defined in the declarations and one expressed externally, then external value is used.
It is an error to attempt to override a system defined prefix.