code: public MapKeyClass<ElementCollection<T>> getOrCreateMapKeyClass()
     {
        Node node = childNode.getOrCreate("map-key-class");
        MapKeyClass<ElementCollection<T>> mapKeyClass = new MapKeyClassImpl<ElementCollection<T>>(this, "map-key-class", childNode, node);
        return mapKeyClass;
     }
docs: If not already created, a new <code>map-key-class</code> element with the given value will be created.
  Otherwise, the existing <code>map-key-class</code> element will be returned.
  @return  a new or existing instance of <code>MapKeyClass<ElementCollection<T>></code>