the first design element comprises {HEAD ~ a rib} extending from {TAIL ~ the exterior surface}; and 
extending from
the first design element comprises { HEAD ~ a rib } extending from { TAIL ~ the exterior surface } ; and
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH