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