public static function importBuilder(Zend_Feed_Builder_Interface $builder, $format = 'atom')
    {
        $obj = 'Zend_Feed_' . ucfirst(strtolower($format));
        /**
         * @see Zend_Loader
         */
        require_once 'Zend/Loader.php';
        Zend_Loader::loadClass($obj);

        return new $obj(null, null, $builder);
    }