I understand that 0x0 is set to every normal window in background but what about root window. I guess _MB_CURRENT_APP_WINDOW is like _NET_ACTIVE_WINDOW so this property should be updated to indicate current top most window. When tasknav is active then property is set to uncommon value -1 (0xffffffff) so I thought launcher is also indicated by uncommon value 0 but it seems there is no way to fast and correct detect launcher. Thanks anyway.