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