Gets or sets the date last entered into the content control. This cache is used because the date display mask stored on the DateFormat property might not contain all of the information about the date, which might be needed if the date display mask is later changed. If this property is not null, then the current value shall be used to populate the content of the content control by filtering it through the date display mask specified in the DateFormat property, if it's not null. This property has effect only for content controls with type Date.