private function resolveMessageToKeys($message, $key, $callback, $prefix="")
    {
        if (is_array($message)) {
            $_prefix = $prefix ? $prefix.$key."." : $key.".";

            foreach ($message as $_key=>$_message) {
                $this->resolveMessageToKeys($_message, $_key, $callback, $_prefix);
            }

        } else {
            $callback($prefix.$key);
        }
    }