_selectMonth(e) {
      e.preventDefault();
      const target = e.target;
      if (target.className.indexOf("ui5-mp-item") > -1) {
        const timestamp = this._getTimestampFromDom(target);
        this._safelySetTimestamp(timestamp);
        this.fireEvent("change", {
          timestamp: this.timestamp
        });
      }
    }
Selects a month, when the user clicks or presses "Enter" or "Space".
@param { Event } e
@private