The position of the current node in the evaluation context.
The size of the evaluation context.
The error code.
Evaluates a query (given as text) based on the current node, the
context position and the context size. Any namespaces
declared using SXP_addNamespaceDeclaration are used for the
evaluation, as are the variable bindings made using functions like
SXP_addVariableString. Upon completion of the query, the
pending namespace declarations and variable bindings are cleared.