+                                                       ->arrayNode('apps')
+                                                               ->treatNullLike([])
+                                                               ->defaultValue($defaults['facebook']['apps'])
+                                                               ->scalarPrototype()->end()
+                                                       ->end()
+                                                       ->integerNode('height')->min(0)->defaultValue($defaults['facebook']['height'])->end()
+                                                       ->integerNode('width')->min(0)->defaultValue($defaults['facebook']['width'])->end()
+                                               ->end()
+                                       ->end()
+                                       ->arrayNode('icon')
+                                               ->addDefaultsIfNotSet()
+                                               ->children()
+                                                       ->scalarNode('ico')->defaultValue($defaults['icon']['ico'])->end()
+                                                       ->scalarNode('png')->defaultValue($defaults['icon']['png'])->end()
+                                                       ->scalarNode('svg')->defaultValue($defaults['icon']['svg'])->end()
+                                               ->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('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($defaults['locales'])
+                                               #->scalarPrototype()->end()
+                                       ->end()
+                                       ->arrayNode('logo')
+                                               ->addDefaultsIfNotSet()
+                                               ->children()
+                                                       ->scalarNode('alt')->defaultValue($defaults['logo']['alt'])->end()
+                                                       ->scalarNode('png')->defaultValue($defaults['logo']['png'])->end()
+                                                       ->scalarNode('svg')->defaultValue($defaults['logo']['svg'])->end()