code: public function setRefererPolicy(string $refererPolicy):void
      {
          if (!in_array($refererPolicy, self::REFERER_POLICY_VALUES)) {
              throw new MiddlewareException(
                  $this,
                  sprintf(
                      "%s is not a valid CSP referer policy, correct values are: %s (see %s)",
                      $refererPolicy, implode(', ', self::REFERER_POLICY_VALUES),
                      'https://developer.mozilla.org/docs/Web/HTTP/Headers/Content-Security-Policy/referrer'
                  )
              );
          }
          $this->tags['referer'] = $refererPolicy;
      }
docs: Sets the 'referrer' value of the CSP. See the REFERER_POLICY_XYZ class constants for the possible values.
  
  @link https://developer.mozilla.org/docs/Web/HTTP/Headers/Content-Security-Policy/referrer
  @param string $refererPolicy
  @throws MiddlewareException