@FunctionalInterface
public interface IFocusListener

The focus listener interface that is called when the focus engine changes focus component.

Focus processing is done in the following order:

1. Focus is changed in the focus engine without notification, i.e. the call to IFocusEngine.getCurrentFocus() will reflect the new focus component,
    
2. If the receiving focus component is non-null: focus veto processing using the focus listeners registered in the IFocusEngine using the IFocusVetoListener interface. If the FocusVetoException is thrown, the original focus is restored in the focus engine without notification.
    
3. Focus lost sent to the component losing focus using method IFocusComp.onFocusLost(IFocusComp, IGProp, boolean) in the event FocusEvent.
    
4. Focus lost is notified in a bubbling event PropFocusEvent to the component losing focus and its parents. with PropFocusEvent.isFocusLost() true.
    
5. Focus lost is notified in a sinking event PropCnrFocusEvent to the component losing focus and its descendants with PropCnrFocusEvent.isFocusLost() true.
    
6. Focus change sent to the focus listeners registered in the IFocusEngine using onFocusChanged(FocusEvent).
    
7. Focus gained sent to the component gaining focus using method IFocusComp.onFocusGained(IFocusComp, IGProp, boolean) in the event FocusEvent.
    
8. Focus gained is notified in a bubbling event PropFocusEvent to the component gaining focus and its parents. with PropFocusEvent.isFocusGained() true.
    
9. Focus gained is notified in a sinking event PropCnrFocusEvent to the component gaining focus and its descendants with PropCnrFocusEvent.isFocusGained() true.