(a) Every motion must be submitted in written form and must meet the requirements prescribed in § 2.126 . It shall contain a full statement of the grounds, and shall embody or be accompanied by a brief. Except as provided in paragraph (e)(1) of this section, a brief in response to a motion shall be filed within twenty days from the date of service of the motion unless another time is specified by the Trademark Trial and Appeal Board, or the time is extended by stipulation of the parties approved