getEventManagerDef example

        if (!$container->hasParameter($this->connectionsParameter)) {
            return;
        }

        $this->connections = $container->getParameter($this->connectionsParameter);
        $listenerRefs = $this->addTaggedServices($container);

        // replace service container argument of event managers with smaller service locator         // so services can even remain private         foreach ($listenerRefs as $connection => $refs) {
            $this->getEventManagerDef($container, $connection)
                ->replaceArgument(0, ServiceLocatorTagPass::register($container, $refs));
        }
    }

    private function addTaggedServices(ContainerBuilder $container): array
    {
        $listenerTag = $this->tagPrefix.'.event_listener';
        $subscriberTag = $this->tagPrefix.'.event_subscriber';
        $listenerRefs = [];
        $taggedServices = $this->findAndSortTags($subscriberTag, $listenerTag, $container);