diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index 11c9f07816..814ee778ca 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -13,8 +13,8 @@
 /**
  * Returns an array containing the names of system-defined (default) menus.
  *
- * @deprecated in drupal:9.3.0 and is removed from drupal:10.0.0. Use
- *   \Drupal\system\Entity\Menu::loadMultiple() instead.
+ * @deprecated in drupal:9.3.0 and is removed from drupal:10.0.0.
+ *  Use \Drupal\system\Entity\Menu::loadMultiple() instead.
  *
  * @see https://www.drupal.org/node/3027453
  */
diff --git a/core/modules/system/routing.api.php b/core/modules/system/routing.api.php
new file mode 100644
index 0000000000..c082759f42
--- /dev/null
+++ b/core/modules/system/routing.api.php
@@ -0,0 +1,119 @@
+<?php
+
+/**
+ * @file
+ * Sets a dynamic route title using _title_callback in the route defaults.
+ * Callback for providing a route title in a *.routing.yml file.
+ *
+ * @see menu
+ *
+ * @ingroup callbacks
+ */
+
+/**
+ * @defgroup menu Menu and routing system
+ * @{
+ * Define the navigation menus, and route page requests to code based on URLs.
+ *
+ * The Drupal routing system defines how Drupal responds to URLs passed to the
+ * browser. The menu system, which depends on the routing system, is used for
+ * navigation. The Menu module allows menus to be created in the user interface
+ * as hierarchical lists of links.
+ *
+ * @section registering_paths Registering router paths
+ * To register a path, you need to add lines similar to this in a
+ * module.routing.yml file:
+ * @code
+ * block.admin_display:
+ *   path: '/admin/structure/block'
+ *   defaults:
+ *     _content: '\Drupal\block\Controller\BlockListController::listing'
+ *   requirements:
+ *     _permission: 'administer blocks'
+ * @endcode
+ * @todo Add more information here, especially about controllers and what all
+ *   the stuff in the routing.yml file means.
+ *
+ * @section Defining menu links
+ * Once you have a route defined, you can use module.menu_links.yml to
+ * define links for your module's paths in the main Navigation menu or other
+ * menus.
+ *
+ * @todo The rest of this topic has not been reviewed or updated for Drupal 8.x
+ *   and is not correct!
+ * @todo It is quite likely that hook_menu() will be replaced with a different
+ *   hook, configuration system, or plugin system before the 8.0 release.
+ *
+ * Drupal's menu system follows a simple hierarchy defined by paths.
+ * Implementations of hook_menu() define menu items and assign them to
+ * paths (which should be unique). The menu system aggregates these items
+ * and determines the menu hierarchy from the paths. For example, if the
+ * paths defined were a, a/b, e, a/b/c/d, f/g, and a/b/h, the menu system
+ * would form the structure:
+ * - a
+ *   - a/b
+ *     - a/b/c/d
+ *     - a/b/h
+ * - e
+ * - f/g
+ * Note that the number of elements in the path does not necessarily
+ * determine the depth of the menu item in the tree.
+ *
+ * When responding to a page request, the menu system looks to see if the
+ * path requested by the browser is registered as a menu item with a
+ * callback. If not, the system searches up the menu tree for the most
+ * complete match with a callback it can find. If the path a/b/i is
+ * requested in the tree above, the callback for a/b would be used.
+ *
+ * The found callback function is called with any arguments specified
+ * in the "page arguments" attribute of its menu item. The
+ * attribute must be an array. After these arguments, any remaining
+ * components of the path are appended as further arguments. In this
+ * way, the callback for a/b above could respond to a request for
+ * a/b/i differently than a request for a/b/j.
+ *
+ * For an illustration of this process, see page_example.module.
+ *
+ * Access to the callback functions is also protected by the menu system.
+ * The "access callback" with an optional "access arguments" of each menu
+ * item is called before the page callback proceeds. If this returns TRUE,
+ * then access is granted; if FALSE, then access is denied. Default local task
+ * menu items (see next paragraph) may omit this attribute to use the value
+ * provided by the parent item.
+ *
+ * In the default Drupal interface, you will notice many links rendered as
+ * tabs. These are known in the menu system as "local tasks", and they are
+ * rendered as tabs by default, though other presentations are possible.
+ * Local tasks function just as other menu items in most respects. It is
+ * convention that the names of these tasks should be short verbs if
+ * possible. In addition, a "default" local task should be provided for
+ * each set. When visiting a local task's parent menu item, the default
+ * local task will be rendered as if it is selected; this provides for a
+ * normal tab user experience. This default task is special in that it
+ * links not to its provided path, but to its parent item's path instead.
+ * The default task's path is only used to place it appropriately in the
+ * menu hierarchy.
+ *
+ * Everything described so far is stored in the menu_router table. The
+ * menu_links table holds the visible menu links. By default these are
+ * derived from the same hook_menu definitions, however you are free to
+ * add more with menu_link_save().
+ *
+ * To declare a callback for a route title, detail a function with the signature
+ * of callback_set_route_title().
+ *
+ * @see https://drupal.org/developing/api/8/routing
+ */
+
+/**
+ * Callback for providing a route title.
+ *
+ * @param
+ * $get_title (can be a string, entity, int, interface)
+ *
+ * @return string
+ *   The page title string (translated, filtered or encoded if necessary).
+ */
+function callback_set_route_title($get_title) {
+  return $title;
+}