Rule 2104. Stipulations. An agreement between parties or their
attorneys relating to any matter in an action, other than one made
between counsel in open court, is not binding upon a party unless it is
in a writing subscribed by him or his attorney or reduced to the form of
an order and entered. With respect to stipulations of settlement and
notwithstanding the form of the stipulation of settlement, the terms of
such stipulation shall be filed by the defendant with the county clerk.