Breaking Change Since version 1.0.0, the first parameter passed to the wp_nav_menu_item_custom_fields is the menu item ID, instead of the nav menu ID. This should not have a big impact, since the nav menu ID passed was always 0 (not used by core). This is a library plugin. It doesn’t do anything visible on its own. It was written to allow other plugins/themes to add custom fields to menu items easily. See Installation. Development of this plugin is done on GitHub. Pull requests welcome. Please see issues reported there before going to the plugin forum.