about tasker Event: Wallpaper Changed

[鲍俊超]

I found a event [System -> Wallpaper Changed]， 

but the userguide did not explain anything. [http://tasker.dinglisch.net/userguide/en/help/eh_index.html]

the event actually effects, 

guess it will has some var like %WALLPAPER, but none

does anyone know the var ?