code: public function setOperator($pOperator)
      {
          if (empty($pOperator)) {
              $pOperator = self::AUTOFILTER_COLUMN_RULE_EQUAL;
          }
          if ((!in_array($pOperator, self::$operators)) &&
              (!in_array($pOperator, self::$topTenValue))) {
              throw new PhpSpreadsheetException('Invalid operator for column AutoFilter Rule.');
          }
          $this->operator = $pOperator;
  
          return $this;
      }
docs: Set AutoFilter Rule Operator.
  
  @param string $pOperator see self::AUTOFILTER_COLUMN_RULE_*
  
  @throws PhpSpreadsheetException
  
  @return Rule