A retrospective validating Act expressed in sufficiently broad language ('is, and always has been, as valid') applies on an appeal by way of rehearing even where the decision below was made before the Act's commencement, unless the Act's language is not specific enough to set aside a prior court decision. The de facto officer doctrine validates acts of delegation by a public officer who continues to act after the expiry of a fixed term, provided the officer had colourable authority and public reputation as the officeholder. The standard of proof for establishing that a prosecution was authorised by the relevant statutory officer is the balance of probabilities, not beyond reasonable doubt, because authority to prosecute is a jurisdictional prerequisite rather than an element of the offence. Under s 19(4) of the Occupational Safety and Health Act 1984 (WA), a principal is deemed an employer only in relation to matters over which it has control; where the hazard arose from a system of work controlled entirely by the contractor, the principal has no case to answer.
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