property CalendarCombo.AllowCheckBox as VisibleEnum
Specifies whether the label displays a checkbox to the left of the date. When unchecked, no date is selected.

VisibleEnum A VisibleEnum expression that specifies whether the label displays a check box.
By default, the AllowCheckBox property is exHidden. Use the AllowCheckBox property to display a check box left to the date, so a date can be selected or not. Use the CheckImage property to use icons, or EBN files to specify your visual appearance for the control's checkbox. Use the AllowSpin property to display a spin control to change the focused field. Use the Value property to change the checkbox's state as follows: If the Value property is not zero, the check box is checked, else the checkbox is unchecked, and the labels shows grayed. Use the ForeColorDisabled property to specify the color to show the selected date when the checkbox is unchecked. For instance, change the ForeColorDisabled to be the control's BackColor and so no date is displayed when the Value property is 0 or the control's checkbox is un-checked. In VB/NET or C# you may need to use the Date.FromOADate(0) to convert the 0 value to a null date.