code: func (w *Window) render() {
  	w.mgr.Render(w)
  
  	// iterate over widgets
  	for _, widget := range w.widgets {
  		widget.Render()
  	}
  
  	// focus on a widget
  	w.focusWidget()
  }
docs: // render calls the user provided Render and than renders the widgets in the
  // window.