chill-bundles/DependencyInjection/Configuration.php

<?php

namespace Chill\CustomFieldsBundle\DependencyInjection;

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

/**
 * This is the class that validates and merges configuration from your app/config files
 *
 * To learn more see {@link http://symfony.com/doc/current/cookbook/bundles/extension.html#cookbook-bundles-extension-config-class}
 */
class Configuration implements ConfigurationInterface
{
    /**
     * {@inheritDoc}
     */
    public function getConfigTreeBuilder()
    {
        $treeBuilder = new TreeBuilder();
        $rootNode = $treeBuilder->root('chill_custom_fields');
        
        $classInfo = "The class which may receive custom fields";
        $nameInfo = "The name which will appears in the user interface. May be translatable";
        $customizableEntitiesInfo = "A list of customizable entities";

        $rootNode
                ->children()
                    ->arrayNode('customizables_entities')
                    ->info($customizableEntitiesInfo)
                    ->defaultValue(array())
                    ->prototype('array')
                        ->children()
                            ->scalarNode('class')->isRequired()->info($classInfo)->end()
                            ->scalarNode('name') ->isRequired()->info($nameInfo) ->end()
                        ->end()
                    ->end()
                ->end()
            ;

        return $treeBuilder;
    }
}