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