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