When a context change is received , {HEAD ~ the placement} and weight of the ads are reevaluated 370 in accordance with the placement and weight rules of {TAIL ~ the respective ads} 
When a context change is received , { HEAD ~ the placement } and weight of the ads are reevaluated 370 in accordance with the placement and weight rules of { TAIL ~ the respective ads }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL