code: protected function appendFilters($filter1, $filter2, $choiceType)
      {
          $choiceOperatior = '$and';
          if (self::CHOICE_OR == $choiceType) {
              $choiceOperatior = '$or';
          }
  
          return array($choiceOperatior => array($filter1, $filter2));
      }
docs: Append two filters according to $choiceType operator
  
  @param array  $filter1
  @param array  $filter2
  @param string $choiceType
  
  @return array