File: vendor/symfony/symfony/src/Symfony/Component/Serializer/Tests/Fixtures/serialization.xml

<?xml version="1.0" ?>

<serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
                    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                    xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping http://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd">

    <class name="Symfony\Component\Serializer\Tests\Fixtures\GroupDummy">
        <attribute name="foo">
            <group>group1</group>
            <group>group2</group>
        </attribute>

        <attribute name="bar">
            <group>group2</group>
        </attribute>
    </class>

</serializer>