Sets the device event mask (see EventMask) for a widget.
The event mask determines which events a widget will receive from
device. 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 add_device_events for widgets
that are already realized, or if you want to preserve the existing event mask. This function can’t be used with windowless widgets (which
return false from get_has_window); to
get events on those widgets, place them inside a EventBox and receive events on the