You can create an event handler for this event in your applications to determine when the user has attempted to modify text that has been marked as protected in the control. The event handler can be used to notify the user that the text the user is attempting to modify is protected or to display a dialog box that enables the user to make appropriate changes to the text. For example, if the protected area is a date, you can display a dialog box that enables the user to choose a date which can then be applied to the text of the control.
For more information about handling events, see Consuming Events.