The frame may be rectangular, when each side comprises {HEAD ~ at least one projection}, typically a lug, or at least one longitudinal array of {TAIL ~ loops} 
The frame may be rectangular , when each side comprises { HEAD ~ at least one projection } , typically a lug , or at least one longitudinal array of { TAIL ~ loops }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL