A more thorough explanation:

Definition: Mandatory authority refers to legal authority that must be followed and is binding. It is different from persuasive authority, which is not binding. All mandatory authority is a primary source of law, but not all primary sources of law are mandatory authority. The jurisdiction affects whether a legal authority is mandatory or persuasive. Secondary sources of law can never be mandatory authority.

Examples of mandatory authority include:

• Constitutions: Constitutions are mandatory authority because they derive their authority from the people. However, they only bind those who have agreed to be bound. For example, the Constitution of the United States is mandatory authority in every state and every court in the United States. But an individual state's constitution is mandatory authority only within the state's jurisdiction.
• Legislations: Legislations are mandatory authority because they are laws passed by a legislative body. They must be followed by those within the jurisdiction. For example, the Americans with Disabilities Act is mandatory authority in the United States.
• Judicial decisions: Judicial decisions can be mandatory authority if they are from a higher court and follow vertical stare decisis. This means that lower courts must follow the decisions of higher courts. However, horizontal stare decisis is generally not binding. This means that courts of one jurisdiction do not have to follow the decisions of courts in another jurisdiction. For example, a decision by the Supreme Court of the United States is mandatory authority for all lower courts in the United States.

These examples illustrate how mandatory authority is binding and must be followed within a specific jurisdiction. They also show how primary sources of law can be mandatory authority, but secondary sources of law can never be mandatory authority.