 a class that implements 
 the XPathVisitable interface, to have the appropriate method called 
 for each component of the XPath.  Aside from possible other uses, the 
 main intention is to provide a reasonable means to perform expression 
 rewriting.
 
 <p>Each method has the form 
 <code>boolean visitComponentType(ExpressionOwner owner, ComponentType compType)</code>. 
 The ExpressionOwner argument is the owner of the component, and can 
 be used to reset the expression for rewriting.  If a method returns