D.C. Mun. Regs. tit. 15, r. 15-128
Parties with common interests or positions are encouraged to align themselves to make joint oral and written presentations, including briefing and presentation of evidence.
Any alignment of parties shall be without derogation to the right of any party to present a separate point of view where the party position differs from that of the group to which he or she is aligned.
In making any filing where more than one party is in agreement, the parties may jointly file, and in that case, the party filing shall clearly designate the parties who join therein.
Subject to the approval of the Commission, any and all of the parties may, by stipulation in writing filed with the Commission or presented at a hearing, state their agreement upon any matter in a proceeding.
D.C. Mun. Regs. tit. 15, r. 15-128