WHEN: to decide if you will allow the user to enter the control (RETURN .F. prevents access to the control) GOTFOCUS: To react to the user getting into the control. GotFocus fires after When has returned .T. to allow them in. VALID: To determine if you will allow the user to leave the control. (RETURN .F. or RETURN 0 prevents the user from leaving the control) LOSTFOCUS: To react to the use leaving the control. (LostFocus fires after Valid has returned .T. or a number other than 0).