So you go look that ref up, and it will say something like "you cannot do this thing, unless otherwise approved by CASA." The Instrument then becomes your permission to do that thing.
Or it'll say "5.123 It is an offence under strict liability to do this thing - 50 penalty units."
and then a few pages later
"Notwithstanding 5.123, it is a defence in a court of law if this thing is done if:
a) the moon is in Aquarius;
b) the aircraft used is fitted with fully functioning registration letters; and
c) the pilot is a person, other than a person mentioned in CAO 43.2.1, who is a person.