The court has nothing to do with what is not before it.

Explanation

A court may only adjudicate matters properly brought before it in the case at bar — it has no authority to reach out and decide questions not raised by the parties or presented in the pleadings.

Where this applies

• A judge in a breach-of-contract case sua sponte raises an unrelated antitrust issue that neither party briefed, and the appellate court reverses because the trial court exceeded the case before it.
• A family court modifies a custody order to address the parents' property dispute, even though no property claim was filed, and the order is vacated because the court acted on matters not before it.
• A probate judge uses a will contest to rule on the validity of a trust that was never challenged in the proceeding, and the ruling is overturned because the court can only decide what is properly presented to it.