code: public JSONNavi<?> up(int level) {
  		while (level-- > 0) {
  			if (stack.size() > 0) {
  				current = stack.pop();
  				path.pop();
  			} else
  				break;
  		}
  		return this;
  	}
docs: call up() level times.
  
  @param level
  number of parent move.