NamespacePrefixTracker namespacePrefixTracker) {
super(factory, environmentInteractionTracker, namespacePrefixTracker);
variables = new JXPathQualifiedVariables(factory,
namespacePrefixTracker);
functions = new JXPathFunctions(getNamespacePrefixTracker());
expressionContext = JXPathContext.newContext(null);
// switching on lenient mode results in null being returned for
// non existent paths rather than an exception being thrown.
expressionContext.setLenient(true);