I just bought a new to me but very old GY DV550U which seems to serve my purposes very well (until I come into some money!) but it came with a feature that I have no idea what it is for or what it does. There is a metal bar or rail that is mounted on the top of the carry handle just behind the hot shoe mount. It is oh, maybe 6 inches long, has angled sides like it is supposed to accept some light or microphone mount or monitor or something, but I don't know what it is really supposed to do. Anyone know?