function ustring (val) {
  var str = String(val)

  // percent encode as UTF-8
  var encoded = encodeURIComponent(str)
    .replace(ENCODE_URL_ATTR_CHAR_REGEXP, pencode)

  return 'UTF-8\'\'' + encoded
}
Class for parsed Content-Disposition header for v8 optimization

@public
@param {string} type
@param {object} parameters
@constructor