A more thorough explanation:

A derogatory clause is a provision in a legal document, such as a contract or a will, that states that the document or a part of it cannot be changed or revoked. However, such provisions are considered ineffective because a sovereign legislature cannot restrict its successors.

For example, a contract may contain a derogatory clause that prohibits any changes to the terms of the agreement. However, if the parties involved in the contract want to modify the terms, they can do so because the derogatory clause is not legally binding.

Another example of a derogatory clause is a provision that a testator inserts secretly in a will, stating that any later will not having that precise clause is invalid. This clause seeks to protect against a later will that may have been obtained through undue influence, duress, or violence.

Overall, a derogatory clause is ineffective because it cannot restrict the power of a sovereign legislature or prevent changes to a legal document.