37 CFR 42.23: Oppositions, replies, and sur-replies.

(a) Oppositions, replies, and sur-replies must comply with the content requirements for motions and, if the paper to which the opposition, reply, or sur-reply is responding contains a statement of material fact, must include a listing of facts that are admitted, denied, or cannot be admitted or denied. Any material fact not specifically denied may be considered admitted.

(b) All arguments for the relief requested in a motion must be made in the motion. A reply may only respond to arguments raised in the corresponding opposition, patent owner preliminary response, patent owner response, or decision on institution. A sur-reply may only respond to arguments raised in the corresponding reply and may not be accompanied by new evidence other than deposition transcripts of the cross-examination of any reply witness.