{HEAD ~ Each side rail portion} includes {TAIL ~ a horizontal wall} between the inner wall and the mid wall 
{ HEAD ~ Each side rail portion } includes { TAIL ~ a horizontal wall } between the inner wall and the mid wall
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH