code: public function asHtml($value, $config = null)
      {
          if ($value === null) {
              return $this->nullDisplay;
          }
  
          return HtmlPurifier::process($value, $config);
      }
docs: Formats the value as HTML text.
  The value will be purified using [[HtmlPurifier]] to avoid XSS attacks.
  Use [[asRaw()]] if you do not want any purification of the value.
  @param string $value the value to be formatted.
  @param array|null $config the configuration for the HTMLPurifier class.
  @return string the formatted result.