For most purposes this function is deprecated in favor of
g_object_set_data(). However, for historical reasons GTK+ stores
GtkWidget that owns a
GdkWindow as user data on the
GdkWindow. So, custom widget implementations should use
this function for that. If GTK+ receives an event for a
and the user data for the window is non-
NULL, GTK+ will assume the
user data is a
GtkWidget, and forward the event to that widget.
The argument can be
The data is owned by the caller of the method.