DependencyInjection/Configuration.php
private function addBlockSection(ArrayNodeDefinition $rootNode)
    {
        $rootNode
            ->fixXmlConfig('block_theme')
            ->children()
                ->arrayNode('block_themes')
                    ->prototype('scalar')->end()
                    ->example(['@App/block.html.twig'])
                ->end()
            ->end()
        ;
    }
private function addBlockSection(ArrayNodeDefinition $rootNode)
    {
        $rootNode
            ->fixXmlConfig('block_theme')
            ->children()
                ->arrayNode('block_themes')
                    ->prototype('scalar')->end()
                    ->example(['@App/block.html.twig'])
                ->end()
            ->end()
        ;
    }
Add block section.

@param ArrayNodeDefinition $rootNode