§1. Instructions clarify the prescripts of laws and elaborate on and determine the methods to be observed in fulfilling them. They are given for the use of those whose duty it is to see that laws are executed and oblige them in the execution of the laws. Those who possess executive power legitimately issue such instructions within the limits of their competence.
§2. The ordinances of instructions do not derogate from laws. If these ordinances cannot be reconciled with the prescripts of laws, they lack all force.
§3. Instructions cease to have force not only by explicit or implicit revocation of the competent authority who issued them or of the superior of that authority but also by the cessation of the law for whose clarification or execution they were given.
Source: Code of Canon Law (Vatican.va)