code: func (w *Window) keyHandler(ev termbox.Event) (bool, Windower, Widgeter) {
  	if w.focus < 0 || w.focus > len(w.widgets) {
  		return false, w.mgr, nil // not used
  	}
  	return w.widgets[w.focus].KeyHandler(ev), w.mgr, w.widgets[w.focus]
  }
docs: // keyHandler routes event to proper widget.  This is called from queue context
  // so be careful to not use blocking calls.