cannotBeOverwritten example

->end()
            ->end()
        ;
    }

    private function addAccessControlSection(ArrayNodeDefinition $rootNode): void
    {
        $rootNode
            ->fixXmlConfig('rule', 'access_control')
            ->children()
                ->arrayNode('access_control')
                    ->cannotBeOverwritten()
                    ->prototype('array')
                        ->fixXmlConfig('ip')
                        ->fixXmlConfig('method')
                        ->fixXmlConfig('attribute')
                        ->children()
                            ->scalarNode('request_matcher')->defaultNull()->end()
                            ->scalarNode('requires_channel')->defaultNull()->end()
                            ->scalarNode('path')
                                ->defaultNull()
                                ->info('use the urldecoded format')
                                ->example('^/path to resource/')
                            

class MergeTest extends TestCase
{
    public function testForbiddenOverwrite()
    {
        $this->expectException(ForbiddenOverwriteException::class);
        $tb = new TreeBuilder('root', 'array');
        $tree = $tb
            ->getRootNode()
                ->children()
                    ->node('foo', 'scalar')
                        ->cannotBeOverwritten()
                    ->end()
                ->end()
            ->end()
            ->buildTree()
        ;

        $a = [
            'foo' => 'bar',
        ];

        $b = [