{HEAD ~ One side} or both sides of {TAIL ~ the panel} 20′″ may be covered with a layer, such as an outer covering layer 
{ HEAD ~ One side } or both sides of { TAIL ~ the panel } 20′″ may be covered with a layer , such as an outer covering layer
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH