I have no idea about the law behind that, but obviously these guys can say whatever they want and find the case law to back it up.
It is at best an illustration; it is case law at the best which can be learned by precept.
The opinions of the judges in the older cases were derived from the English case law on the subject.
In that case law would have appeared as a jealous master,—its study long, and life very short.
Under the statute of Anne it was protected by case law, "book" being held to include a volume or sheet of music.