This case (at [83-91]) tells you almost everything you need to know about the use of extrinsic materials4. They may be consulted to reveal legislative purpose. But what about using them to determine meaning? Purpose and meaning are ‘inextricably woven’5.
Section 15AB(1) of the Acts Interpretation Act makes the use of extrinsic materials depend on them being ‘capable of assisting in the ascertainment of meaning’ – a frustratingly enigmatic test. Two things are clear in practice, however – (A) extrinsic materials cannot displace clear meaning6, and (B) they must not be substituted for the text7. iTip – always take care with extrinsic materials!
This case is from Episode 27 of interpretationNOW!
4 See also Episode 15.