{HEAD ~ The only action} taken by a prospective user is to pull {TAIL ~ a single stair tread} down 
{ HEAD ~ The only action } taken by a prospective user is to pull { TAIL ~ a single stair tread } down
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH