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