code: public String result(int positionNum) {
  		Pair<Integer, Integer> kv = null;
  		if (null != (kv = position(positionNum, false))) {
  			return doSubstring(kv);
  		}
  		
  		return EMPTY;
  	}
docs: Returns the substring in given range with given left position number
  
  @param positionNum
  @return