A retainer extends about {TAIL ~ the periphery} of the skylight for holding the panels on {HEAD ~ the frame} means 
A retainer extends about { TAIL ~ the periphery } of the skylight for holding the panels on { HEAD ~ the frame } means
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH