Handling Keyboard Focus
A control with keyboard focus receives keyboard events. The Dialog Manager tests to see which control has keyboard focus when a keyboard event is processed and sends the event to that control. If no control has keyboard focus, the keyboard event is discarded. Currently, the list box, clock, and editable text controls are the only standard system controls that support keyboard focus. A control retains keyboard focus if it is hidden or deactivated.A focus ring is drawn around the control with keyboard focus. When creating your own controls, allow space for the focus ring. For more details on designing with focus rings, see Mac OS 8 Human Interface Guidelines.
Keyboard focus is only available if an embedding hierarchy has been established in the focusable control's window. The default focusing order is based on the order in which controls are added to the window. For more details on embedding hierarchies, see "Embedding Controls".