[ooc] good question, here is a bit I found on US bills, I think the australian system which I know is about the same.
U.S. statutory law is organized into 50 books, known as titles. Each title should contain only those laws that have to do with a discrete subject area. In addition, it should only contain general and permanent laws — excluding provisions that apply only for a limited time (e.g., an annual appropriations law) or to a small number of people (e.g., a private law). For example, Title 7 should only contain permanent laws having to do with agriculture. Title 28 should only concern the judiciary and judicial procedure.
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