public function upperWords($delimiters = null)
    {
        if (is_null($delimiters)) {
            $delimiters = " \t\r\n\f\v";
        }

        if (
            (version_compare(PHP_VERSION, '5.4.32', '>=') && version_compare(PHP_VERSION, '5.5.0', '<')) ||
            version_compare(PHP_VERSION, '5.5.16', '>=')
        ) {
            return $this->transform('ucwords', $delimiters);
        } else {
            return $this->transform('ucwords');
        }
    }