Class PythonElementClassLookup

                  object --+        
                           |        
    etree.ElementClassLookup --+    
                               |    
etree.FallbackElementClassLookup --+
                                   |
                                  PythonElementClassLookup

Element class lookup based on a subclass method.

To use it, inherit from this class and override the method

    lookup(self, document, node_proxy)

to lookup the element class for a node. The first argument is the opaque
document instance that contains the Element. The second arguments is a
lightweight Element proxy implementation that is only valid during the
lookup. Do not try to keep a reference to it. Once the lookup is done, the
proxy will be invalid.

If you return None from this method, the fallback will be called.