Processes keydown events.
    keydown(event)
    
    
        | event | DOM Event, event object corresponding to keydown event | 
    
 
Returns 
undefined.
Description
This method is called internally when a keyboard button is pressed and will process keyboard events (up/down, left/right, enter, space, etc).
This method emits 
.onKeydown event.
This method can be overwritten: