code: function icalrecur_toString() {
        // TODO retain order
        var str = "FREQ=" + this.freq;
        if (this.count) {
          str += ";COUNT=" + this.count;
        }
        if (this.interval > 1) {
          str += ";INTERVAL=" + this.interval;
        }
        for (var k in this.parts) {
          /* istanbul ignore else */
          if (this.parts.hasOwnProperty(k)) {
            str += ";" + k + "=" + this.parts[k];
          }
        }
        if (this.until) {
          str += ';UNTIL=' + this.until.toICALString();
        }
        if ('wkst' in this && this.wkst !== ICAL.Time.DEFAULT_WEEK_START) {
          str += ';WKST=' + ICAL.Recur.numericDayToIcalDay(this.wkst);
        }
        return str;
      }
docs: The string representation of this recurrence rule.
  @return {String}