protected function findTags(ContainerBuilder $container, $tagName, $argumentPosition, $ext = false): void
    {
        $services = [];

        foreach ($container->findTaggedServiceIds($tagName) as $serviceId => $tag) {
            $class = isset($tag[0]['class'])
                ? $this->getRealClassName($container, $tag[0]['class'])
                : $this->getClassName($container, $serviceId, $tagName);
            $class = $this->findResolveTarget($container, $class);
            $this->replaceResolveTargetClass($container, $tagName, $serviceId, $class);

            // Flip, because we want tag classe names (= type identifiers) as keys
            if ($ext) {
                $services[$class][] = $serviceId;
            } else {
                $services[$class] = $serviceId;
            }
        }

        $container->getDefinition('fxp_default_value.extension')->replaceArgument($argumentPosition, $services);
    }