public static function chain_transformations($options, $transformations)
    {
        $transformations = \Cloudinary::build_array($transformations);
        // preserve url options
        $url_options = self::array_subset($options, self::$URL_KEYS);
        array_unshift($transformations, $options);
        $url_options["transformation"] = $transformations;
        return $url_options;
    }