By default, the AllowSelectDateRect property is exLeftClick + exALTKey, which means that the user can hold the ALT key while pressing the left mouse button and so a rectangle is shown, and each date that intersect the rectangular region will be selected by dragging the mouse.  

The exDisallow indicates the the user can not rectangular select dates in the calendar panel. Once the user starts selecting a new date in the calendar panel, the control fires the LayoutStartChanging(exCalendarSelectionChange). Once a new date is selected, the LayoutEndChanging(exCalendarSelectionChange) event occurs. The SingleSel property indicates whether the user can select one or multiple dates. The AllowSelectDate specifies the keys combination so the user can do a selection in the calendar panel. Use the Selection/SelectDate property to change programmatically the dates being selected in the calendar, including the dates to be shown in the schedule view. You can use the Selection/SelCount/SelDate property to retrieve the selected dates. You can do the same type of the selection in the schedule panel, by using the AllowSelectEventRect property. 

The ClipToSel property indicates whether the control clips the schedule panel to view the selected dates only. The FitSelToView method restores the view to fit the selected dates.

The following screen shot shows the rectangular selection, in the calendar panel: