selecting {HEAD ~ content} for and distributing {TAIL ~ content} to users based on their association with the affinity group 
selecting { HEAD ~ content } for and distributing { TAIL ~ content } to users based on their association with the affinity group
OTH HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH