code: def find(self, qref, classes=()):
          
          if not len(classes):
              classes = (self.__class__,)
          if self.qname == qref and self.__class__ in classes:
              return self
          for c in self.rawchildren:
              p = c.find(qref, classes)
              if p is not None:
                  return p
          return None
docs: Find a referenced type in self or children.
          @param qref: A qualified reference.
          @type qref: qref
          @param classes: A list of classes used to qualify the match.
          @type classes: [I{class},...]
          @return: The referenced type.
          @rtype: L{SchemaObject}
          @see: L{qualify()}