If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  If OpenWindow(1,0,0,100,100,"Window 2",#PB_Window_SystemMenu|#PB_Window_ScreenCentered,WindowID(0))
  EndIf
  EnableWindow_(WindowID(0),0)
Repeat : Until WaitWindowEvent() = #PB_Event_CloseWindow
EndIf