AutoPostBackOnSelectionChanged:
Selected Dates:
You can select and deselect multiple days by clicking a single day, day header selector, week selector or month selector.

If the AutoPostBackOnSelectionChanged property of UltimateCalendar is set to True it will postback the selected days in the SelectedDays collection of the control.

If it is False you can use the Client-side API to get the selected dates without going back to server.