private function addApple($os)
    {
        $config = $this->root->
            children()->
                arrayNode($os)->
                    children()->
                        scalarNode("timeout")->defaultValue(60)->end()->
                        booleanNode("sandbox")->defaultFalse()->end()->
                        scalarNode("pem")->cannotBeEmpty()->end()->
                        scalarNode("passphrase")->defaultValue("")->end()->
                        scalarNode('json_unescaped_unicode')->defaultFalse();
                        if (method_exists($config,'info')) {
                            $config = $config->info('PHP >= 5.4.0 and each messaged must be UTF-8 encoding');
                        }
                        $config->end()->
                    end()->
                end()->
            end()
        ;
    }