allows external instances to register as veto listener for the button's actions.
An ::com::sun::star::form::XApproveActionListener returning false on
it's approve-method will prevent any action which would usually be triggered - this includes
not only submitting or resetting forms, but also calling the
::com::sun::star::awt::XActionListeners of the super service
This may be interesting for e.g. forms which want to provide input validation before submitting
data.
