code: public function getRule($pIndex)
      {
          if (!isset($this->ruleset[$pIndex])) {
              $this->ruleset[$pIndex] = new Column\Rule($this);
          }
  
          return $this->ruleset[$pIndex];
      }
docs: Get a specified AutoFilter Column Rule.
  
  @param int $pIndex Rule index in the ruleset array
  
  @return Column\Rule