Used when a form needs to return some kind of a \Symfony\Component\HttpFoundation\Response object, e.g., a \Symfony\Component\HttpFoundation\BinaryFileResponse when triggering a file download. If you use self::setRedirect() or self::setRedirectUrl(), it will be used to build a \Symfony\Component\HttpFoundation\RedirectResponse and will populate this key.
Type: \Symfony\Component\HttpFoundation\Response|null
File
core/lib/Drupal/Core/Form/FormState.php, line 128
Class
FormState Stores infor