{TAIL ~ a substrate} capable of transmitting visible light and having {HEAD ~ a pair} of opposing surfaces 
{ TAIL ~ a substrate } capable of transmitting visible light and having { HEAD ~ a pair } of opposing surfaces
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH