code: func focusWindow(w *Window) {
  	if w == nil {
  		return
  	}
  	_, found := windows[w.id]
  	if !found {
  		return
  	}
  	if focus == w {
  		return
  	}
  	prevFocus = focus
  	focus = w
  
  	resizeAndRender(w)
  }
docs: // focus on provided window. This will implicitly focus on a window widget
  // that can have focus.  Render and flush it onto the terminal.
  // focus shall be called from queue context.