code: protected function isActiveFrontendFilterValue($arrWidget, $arrFilterUrl, $strKeyOption)
      {
          // Special case, the "empty" value first.
          if (empty($strKeyOption) && !isset($arrFilterUrl[$arrWidget['eval']['urlparam']])) {
              return true;
          }
          $blnIsActive = isset($arrFilterUrl[$arrWidget['eval']['urlparam']])
              && ($arrFilterUrl[$arrWidget['eval']['urlparam']] == $strKeyOption);
          if (!$blnIsActive && $this->get('defaultid')) {
              $blnIsActive = ($arrFilterUrl[$arrWidget['eval']['urlparam']] == $this->get('defaultid'));
          }
          return $blnIsActive;
      }
docs: Returns if the given value is currently active in the given filter settings.
  
  @param array  $arrWidget    The widget information.
  
  @param array  $arrFilterUrl The filter url parameters to use.
  
  @param string $strKeyOption The option value to determine.
  
  @return bool  true If the given value is mentioned in the given filter parameters, false otherwise.