+                                       ->arrayNode('facebook')
+                                               ->addDefaultsIfNotSet()
+                                               ->children()
+                                                       ->arrayNode('apps')
+                                                               ->treatNullLike([])
+                                                               ->defaultValue($defaults['facebook']['apps'])
+                                                               ->scalarPrototype()->end()
+                                                       ->end()
+                                                       ->integerNode('height')->min(0)->defaultValue($defaults['facebook']['height'])->end()
+                                                       ->integerNode('width')->min(0)->defaultValue($defaults['facebook']['width'])->end()
+                                               ->end()
+                                       ->end()