code: public ExtensibleType<TldExtensionType<T>> getOrCreateExtensionElement()
     {
        List<Node> nodeList = childNode.get("extension-element");
        if (nodeList != null &&  nodeList.size() > 0)
        {
           return new ExtensibleTypeImpl<TldExtensionType<T>>(this, "extension-element", childNode, nodeList.get(0));
        }
        return createExtensionElement();
     }
docs: If not already created, a new <code>extension-element</code> element will be created and returned.
  Otherwise, the first existing <code>extension-element</code> element will be returned.
  @return the instance defined for the element <code>extension-element</code>