code: protected function getCustomizationOptions(ContainerInterface $container, $requestedName, array $options = null)
      {
          if (!static::OPTIONS_NAME) {
              throw new \RuntimeException('The class constants "OPTIONS_NAME" must be non empty.');
          }
  
          return $container->get(static::OPTIONS_NAME);
      }
docs: Get the customization options.
  
  @param ContainerInterface $container
  @param string             $requestedName
  @param array              $options
  
  @return \Core\Options\FieldsetCustomizationOptions
  @throws \RuntimeException