protected function _getValidContentNodeData($contentNode) {
        $contentNode = $contentNode instanceof Garp_Util_Configuration ? $contentNode : new Garp_Util_Configuration($contentNode);
        $contentNode
            ->obligate('model')
            ->obligate('data')
            ->obligate('columns')
            ->setDefault('type', '')
            ->setDefault('classes', '')
        ;
        return $contentNode;
    }