a) {TAIL ~ a door} mounted on a frame for lateral movement on {HEAD ~ tracks} between a first open position and a second closed position 
a ) { TAIL ~ a door } mounted on a frame for lateral movement on { HEAD ~ tracks } between a first open position and a second closed position
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH