Notified when a key is pressed. To use onKeyDown, you must create a listener object. 
You can then define a function for onKeyDown and use addListener() to register the listener with the Key object, as shown in the following example: 
var keyListener:Object = new Object();
keyListener.onKeyDown = function() {
    trace("DOWN -> Code: "+Key.getCode()+"\tACSII: "+Key.getAscii()+"\tKey: "+chr(Key.getAscii()));
};
keyListener.onKeyUp = function() {
    trace("UP -> Code: "+Key.getCode()+"\tACSII: "+Key.getAscii()+"\tKey: "+chr(Key.getAscii()));
};
Key.addListener(keyListener);