A discriminated union that references a discriminant value in another
widget and contains one of several cases (widgets). To have a case
hold more than one widget or to use a different id for the case than
for the widget id, just wrap the widget(s) in a container widget named
with the desired case id.
version: $Id: Union.java 462520 2006-10-10 19:39:14Z vgritsenko $
initialize() Called after widget's environment has been setup,
to allow for any contextual initalization such as
looking up case widgets for union widgets.