{HEAD ~ The interface region} is, at least in part, transmissive of {TAIL ~ radiant energy} 
is transmissive of
{ HEAD ~ The interface region } is , at least in part , transmissive of { TAIL ~ radiant energy }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL