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