+                                       ->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($defaults['facebook']['width'])->end()
+                                               ->end()
+                                       ->end()
+                                       ->scalarNode('locale')->cannotBeEmpty()->defaultValue($defaults['locale'])->end()
+                                       #TODO: see if we can't prevent key normalisation with ->normalizeKeys(false)
+                                       #->scalarNode('locales')->cannotBeEmpty()->defaultValue($defaults['locales'])->end()
+                                       ->variableNode('locales')
+                                               ->treatNullLike([])
+                                               ->defaultValue($defaults['locales'])
+                                               #->scalarPrototype()->end()
+                                       ->end()
+                                       #TODO: see if we can't prevent key normalisation with ->normalizeKeys(false)
+                                       #->scalarNode('languages')->cannotBeEmpty()->defaultValue($defaults['languages'])->end()
+                                       ->variableNode('languages')
+                                               ->treatNullLike([])
+                                               ->defaultValue($defaults['languages'])
+                                               #->scalarPrototype()->end()
+                                       ->end()
+                                       ->scalarNode('path')->defaultValue($defaults['path'])->end()
+                                       #->arrayNode('public')
+                                       #       ->addDefaultsIfNotSet()
+                                       #       ->children()
+                                       #               ->scalarNode('path')->defaultValue($defaults['public']['path'])->end()
+                                       #               ->scalarNode('url')->defaultValue($defaults['public']['url'])->end()
+                                       #       ->end()
+                                       #->end()