docs: def register_form_factory(Form, app):
      """Return extended registration form."""
      if app.config.get('RECAPTCHA_PUBLIC_KEY') and \
              app.config.get('RECAPTCHA_PRIVATE_KEY'):
          class RegisterForm(Form):
              recaptcha = FormField(RegistrationFormRecaptcha, separator='.')
  
          return RegisterForm
  
      return Form