(such as all controls and \helpref{wxApp}{wxapp})
can hold arbitrary data which is here referred to as "client data".
This is useful e.g. for scripting languages which need to handle
-shadow objects for most of wxWindows' classes and which store
+shadow objects for most of wxWidgets' classes and which store
a handle to such a shadow class as client data in that class.
This data can either be of type void - in which case the data
{\it container} does not take care of freeing the data again