Rule of Decision
Precedent defined as a controlling rule that informs the decision-maker how they are to rule on a particular legal question, is a type of rule of decision because it removes a degree of discretion from the decision-maker.
The Supremacy Clause, Article VI, is a constitutional rule of decision compelling all government officials to recognize the federal constitution and any statutes created by Congress in compliance with the constitution to be the supreme law of the land before which all other conflicting decisional rules must fall. State constitutional rules and state statutes must fall when they conflict with the supreme law. This rule of decision unequivocally establishes that state family law codes that conflict with the federal constitution are void and unenforceable.