code: public function prepend(ContainerBuilder $container)
      {
          $configs = $container->getExtensionConfig($this->getAlias());
          $config = $this->processConfiguration($this->getConfiguration($configs, $container), $configs);
  
          foreach ($this->service_sources as $service_source) {
              $result = $service_source->prepend($container, $config);
              if (null !== $result) {
                  $container->prependExtensionConfig($this->getAlias(), $result);
              }
          }
      }
docs: {@inheritdoc}