RequestModule provides access to Request object properties.
To get access to request properties use XPath syntax, e.g. to get the request
context path use 'contextPath' as the attribute name.
More complex expressions are also supported, e.g.:
'userPrincipal/name'
will return the name property of the Principal object returned by the
request.getUserPrincipal() method. If requested object is not found then
an exception will be thrown.
Returns the object which should be used as JXPath context.
Descendants should override this method to return a specific object
that is requried by the implementing class.
Examples are: request, session and application context objects.