File: vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/Fixtures/xml/serializer_enabled.xml

<?xml version="1.0" encoding="utf-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony http://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <framework:serializer enabled="true" />
    </framework:config>
</container>