In one embodiment, the nodes store data to track {TAIL ~ protection levels} of {HEAD ~ their children nodes} 
In one embodiment , the nodes store data to track { TAIL ~ protection levels } of { HEAD ~ their children nodes }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD