_selectDate(e, isShift) {
      const target = e.target;
      if (!this._isDayPressed(target)) {
        return;
      }
      const timestamp = this._getTimestampFromDom(target);
      this._safelySetTimestamp(timestamp);
      this._updateSecondTimestamp();
      if (this.selectionMode === _CalendarSelectionMode.default.Single) {
        this.selectedDates = [timestamp];
      } else if (this.selectionMode === _CalendarSelectionMode.default.Multiple) {
        if (this.selectedDates.length > 0 && isShift) {
          this._multipleSelection(timestamp);
        } else {
          this._toggleTimestampInSelection(timestamp);
        }
      } else {
        this.selectedDates = this.selectedDates.length === 1 ? [...this.selectedDates, timestamp] : [timestamp];
      }
      this.fireEvent("change", {
        timestamp: this.timestamp,
        dates: this.selectedDates
      });
    }
Selects/deselects a day.
@param { Event} e
@param { boolean} isShift true if the user did Click+Shift or Enter+Shift (but not Space+Shift)
@private