Translations:Manual:$wgConf/13/en

When extracting global settings, the object will search first the more specific level (the first one in the list above) and if it doesn't find the setting, it will search in less specific levels. When it finds one, if won't search for less specific ones. This means that you have to pay attention for some specific settings, such as $GroupPermissions, because it doesn't merge the setting with less specific levels, nor the default value (the one in DefaultSettings.php), you'll need to do it by yourself.