GUIGetMsg() and Middle mouse button

[Yves1Fix]

GUIGetMsg() pools the following events :

$GUI_EVENT_PRIMARYDOWN

$GUI_EVENT_PRIMARYUP

$GUI_EVENT_SECONDARYDOWN

$GUI_EVENT_SECONDARYUP

but what about the middle mouse button ?

I am looking for something like $GUI_EVENT_{middle mouse button}DOWN

but I didn't find it.

Any help ?

Thanks

Yves