Devices for holding wings open; Devices for limiting opening of wings or for holding wings open by a movable member extending between frame and wing; Braking devices, stops or buffers, combined therewith by mechanical means with a device carried on the wing for frictional or like engagement with a fixed flat surface, e.g. {for holding wings open or closed by} retractable feet {of the pivoted lever or eccentric type, e.g. for sliding windows}