XPathVariableResolver provides access to the set of user defined XPath variables.
The XPathVariableResolver and the XPath evaluator must adhere to a contract that
cannot be directly enforced by the API. Although variables may be mutable,
that is, an application may wish to evaluate the same XPath expression more
than once with different variable values, in the course of evaluating any
single XPath expression, a variable's value must be immutable. |