Sets the event mask (see GdkEventMask) for a widget. The event mask determines which events a widget will receive. Keep in mind that different widgets have different default event masks, and by changing the event mask you may disrupt a widget’s functionality, so be careful. This function must be called while a widget is unrealized. Consider Widget.addEvents for widgets that are already realized, or if you want to preserve the existing event mask. This function can’t be used with widgets that have no window. (See Widget.getHasWindow). To get events on those widgets, place them inside a gtk.EventBox and receive events on the event box.