A block placement generator arranges sets of {TAIL ~ the interface objects} into block configurations within {HEAD ~ the interface} 
A block placement generator arranges sets of { TAIL ~ the interface objects } into block configurations within { HEAD ~ the interface }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD