REMOVE-CALLBACK, the
client-data passed must be EQUAL to the client-data
passed to ADD-CALLBACK.
REMOVE-CALLBACK, etc., the function may be
supplied as either 'FUNCTION or #'FUNCTION.
However, they are considered different so use the same one
when adding and removing callbacks.
XmNitems resources for
List widgets and relatives. Instead, use (SET-ITEMS
<widget> ....) and (GET-ITEMS <widget>).