The first edge is pressed against {HEAD ~ the first rail element} through a first protruding portion of {TAIL ~ the first edge} 
The first edge is pressed against { HEAD ~ the first rail element } through a first protruding portion of { TAIL ~ the first edge }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL