docs: function hwbString(hwb, alpha) {
     if (alpha === undefined) {
        alpha = (hwb[3] !== undefined ? hwb[3] : 1);
     }
     return "hwb(" + hwb[0] + ", " + hwb[1] + "%, " + hwb[2] + "%"
             + (alpha !== undefined && alpha !== 1 ? ", " + alpha : "") + ")";
  }