To be called on NEXT, APPLY, and FINISH events.
Validates this panel and returns true if valid, false if not.
If true, this also writes the panel's data into the provided
Called upon receipt of a NEXT event. If this returns true,
the Bali wizard proceeds to the next panel. If this returns
false, the wizard cancels the event and does not proceed.
Called upon receipt of a FINISH or APPLY event. If true is
returned, the Bali wizard tells continues the finish or apply
sequence and tells the state to commit. If false is returned, the
event is canceled and nothing else happens.