Abstract: Doors such as garage doors are commonly mounted with respect to a door opening so as to be capable of being moved between a closed position in which such a door extends vertically across the opening and an opened position in which such a door extends substantially horizontally adjacent to the top of the door opening. An auziliary door such as a screen door for enclosing such an opening when such a principal door is in an opened position may be mounted on such a principal door so that it is capable of being moved along with the principal door between the opened and closed positions of the principal door and so that it can be moved to enclose the door opening when the principal door is in an opened position.