[flexcoders] How to enable keyboard input in a Box?

[mitchgrrt]

I have a thing I'm drawing on screen using a Box and some graphics.  I
would like it to also respond to some keyboard events.  (It responds
well to mouse clicks and drag events.)  Key clicks  don't seem to work:
box.focusEnabled = true;
box.addEventListener(KeyboardEvent.KEY_DOWN, onKeyDown);
The onKeyDown method never gets called.  Is there a way to do this? 
Thanks.