A more thorough explanation:

The grand coutumier de pays et duché de Normandie is a collection of the common or customary laws of the Duchy of Normandy. It was probably compiled in the 13th century and is still the law of Jersey, except to the extent that it has been modified by later legislation and judicial decisions.

If someone wants to know the laws that were followed in the Duchy of Normandy, they can refer to the grand coutumier de pays et duché de Normandie. It is a historical document that provides insight into the legal system of that time.

The clameur de haro is an outcry recognized in the Channel Islands as a protest against trespass to land. It is a legal remnant of when the Duchy of Normandy held the islands before England took control in the 13th century. The victim's cry of haro (repeated 3 times) is popularly supposed to be an abbreviation of Ha Rollo, the first Duke of Normandy. The full cry, Haro, Haro, Haro, a l'aide, mon prince, on me fait tort, when registered at the local records office, enjoins the offender from possessing the land.

If someone is being trespassed upon, they can use the clameur de haro to protest against it. By shouting "Haro, Haro, Haro, a l'aide, mon prince, on me fait tort," they can register their complaint and prevent the offender from possessing the land. This tradition is still followed in the Channel Islands today.