What is the difference between principal and amending legislation?

Acts and Regulations may be Principal or Amending.

Principal

A principal Act or Regulation is the major document covering the law on that particular subject or area eg. Crimes Act 1900 (NSW) or Relationships Act 2008 (VIC).

Amending

An amending Act or Regulation makes changes to another Act or Regulation, usually a principal Act or Regulation. The changes may affect a few words, replace entire sections or delete (“repeal” or “revoke”) a complete Act or Regulation. It is generally easy to recognise amending legislation from the title, which will usually include the word “Amendment”, or “Amending”.

An exception to this is that principal legislation may amend (including repeal and revoke) other principal legislation.