Issue #3271585 by rromore, rhys: BooleanSetting using value of markup instead of raw value

    $output = $this->renderer->render($build);

    // Process the rendered content using PHP coersion.

    $output = trim(strip_tags($output));

    $result = filter_var($output, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE);

    // Respond using the values provided by the configuration.

    if ($this->configuration['string']) {

      return ['#markup' => $result ? $this->configuration['on'] : $this->configuration['off']];

    }

    return ['#markup' => $result];

  }

}