Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition::append PHP Method

    public function append(NodeDefinition $node)
    {
        $this->children[$node->name] = $node->setParent($this);
        return $this;
    }

 /**
  * @param ArrayNodeDefinition $dataNode
  */
 protected function appendDataNodes($dataNode)
 {
     $treeBuilder = new TreeBuilder();
     $assetsNode = $treeBuilder->root('assets');
     $assetsNode->useAttributeAsKey('asset-identifier')->normalizeKeys(false)->prototype('array')->children()->arrayNode('inputs')->info('Input assets list')->prototype('scalar')->end()->end()->arrayNode('filters')->info('Filters to manipulate input assets')->prototype('scalar')->end()->end()->scalarNode('output')->info('Output asset')->end()->end()->end();
     $dataNode->append($assetsNode);
 }