code: func (ptree *ptree) Query(start, stop common.Comparator) common.Comparators {
  	cmps := make(common.Comparators, 0, 32)
  	aa := newApplyAction(func(cmp common.Comparator) bool {
  		cmps = append(cmps, cmp)
  		return true
  	}, start, stop)
  	ptree.checkAndRun(aa)
  	aa.completer.Wait()
  	return cmps
  }
docs: // Query will return a list of Comparators that fall within the
  // provided start and stop Comparators.  Start is inclusive while
  // stop is exclusive, ie [start, stop).