A top cap member mounts on and extends horizontally along the top frame element, and is constructed of {HEAD ~ a material} which permits {TAIL ~ at least limited transverse flexibility} 
permits
A top cap member mounts on and extends horizontally along the top frame element , and is constructed of { HEAD ~ a material } which permits { TAIL ~ at least limited transverse flexibility }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL