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