+ ChildFactory
+ is useful for creating node children lazily on a background thread,
+ and for simplifying working with Children.Keys. One oversight in
+ the original API was providing for notification that the ChildFactory
+ is no longer in use and should clean up any resources and detach
+ any listeners it can.
+
+ ChildFactory.Detachable is an abstract class which adds
+ addNotify() and removeNotify() methods to ChildFactory. addNotify()
+ is called immediately before the first call to createKeys() after
+ creation or a call to removeNotify().
+
+