code: public ExtensibleType<ExtensibleType<T>> getOrCreateExtensibleType()
     {
        Node node = childNode.getOrCreate("extensibleType");
        ExtensibleType<ExtensibleType<T>> extensibleType = new ExtensibleTypeImpl<ExtensibleType<T>>(this, "extensibleType", childNode, node);
        return extensibleType;
     }
docs: If not already created, a new <code>extensibleType</code> element with the given value will be created.
  Otherwise, the existing <code>extensibleType</code> element will be returned.
  @return  a new or existing instance of <code>ExtensibleType<ExtensibleType<T>></code>