Action to which this Part applies taken to be lawful
All action to which this Part applies is taken for all purposes to have been lawful when it occurred.
S5 defines action under the act as action by a Commonwealth officer in relation to the Tampa, the Aceng or any other refugee boat during the validation period.
S4 sets up a validaiton period from 27 August 2001 to the act's commencement on 21 September 2001.
The act does not seem to deal with tax law, but it is retrospective. Evidently it's not just war crimes where the Man of Steel advocates retrospectivity.