Symfony: use semantic configuration combining yml and xml configuration files

app.xml

<?xml version="1.0" ?>
<!-- app/config/app.xml -->
<sym:container xmlns:sym="http://symfony.com/schema/dic/services" xmlns="http://example.org/schema/dic/app">

    <config>

        <some_integer>86</some_integer>

        <array_element name="first_from_xml">
            <integer_element>3</integer_element>
            <text_element>text1 from xml</text_element>
        </array_element>
        <array_element name="second_from_xml">
            <integer_element>4</integer_element>
            <text_element>text2 from xml</text_element>
        </array_element>
    </config>

</sym:container>

app.yml

# app/config/app.yml
app:
    some_integer: 1
    some_text: value_from_app
    array_elements:
        first_from_yml:
            integer_element: 1
            text_element: text1 from yml
        second_from_yml:
            integer_element: 2
            text_element: text2 from yml

config.yml

# app/config/config.yml
# Include both semantic configs
imports:
    - { resource: app.yml }
    - { resource: app.xml }

Configuration.php

<?php

// src/AppBundle/DependencyInjection/Configuration.php

namespace AppBundle\DependencyInjection;

use Symfony\Component\Config\Definition\Builder\TreeBuilder;
use Symfony\Component\Config\Definition\ConfigurationInterface;

class Configuration implements ConfigurationInterface
{
    /**
     * Generates the configuration tree builder.
     *
     * @return \Symfony\Component\Config\Definition\Builder\TreeBuilder The tree builder
     */
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new TreeBuilder();
        $rootNode = $treeBuilder->root('app');

        $rootNode
            ->fixXmlConfig('array_element')
            ->children()
                ->arrayNode('array_elements')
                    ->useAttributeAsKey('name')
                    ->prototype('array')
                        ->children()
                            ->integerNode('integer_element')->end()
                            ->scalarNode('text_element')->end()
                        ->end()
                    ->end()
                ->end()
                ->integerNode('some_integer')->defaultValue('0')->end()
                ->scalarNode('some_text')->end()

            ->end();

        return $treeBuilder;
    }
}