Transparent focus traversal is one of key features of FX/Swing interoperability. This includes both directions:

1. Transferring focus from Swing to FX. JFXPanel should accept Swing focus and dispatch it to proper SceneGraph nodes.
2. Transferring focus from FX to Swing. When FX focus reaches the beginning/end of the focus chain, focus should be transferred out to Swing.

#1 is currently implemented as a part of EmbeddedStageInterface. To support #2, there should be an ability to register a listener for focus "wraps": when TraversalEngine detects that focus reaches the beginning/end of the focus loop, it should ask the listener if it's able to dispatch focus out of FX scene.