public function appendConfiguration(ArrayNodeDefinition $rootNode)
    {
        $rootNode
            ->children()
                ->arrayNode('messages')
                    ->addDefaultsIfNotSet()
                    ->children()
                        ->arrayNode('languages')->performNoDeepMerging()->prototype('scalar')->end()->defaultValue(array('nl', 'en', 'fr'))->end()
                        ->booleanNode('overwrite_compatibility')->defaultTrue()->end()
                        ->scalarNode('yaz_cleanup')->end()
                    ->end()
                ->end()
            ->end()
        ;
    }