diff --git a/wp-admin/includes/plugin.php b/wp-admin/includes/plugin.php
index e4018d7a13..1c328f363c 100644
--- a/wp-admin/includes/plugin.php
+++ b/wp-admin/includes/plugin.php
@@ -1060,7 +1060,9 @@ function uninstall_plugin($plugin) {
  * @param string   $page_title The text to be displayed in the title tags of the page when the menu is selected.
  * @param string   $menu_title The text to be used for the menu.
  * @param string   $capability The capability required for this menu to be displayed to the user.
- * @param string   $menu_slug  The slug name to refer to this menu by (should be unique for this menu).
+ * @param string   $menu_slug  The slug name to refer to this menu by. Should be unique for this menu page and only
+ *                             include lowercase alphanumeric, dashes, and underscores characters to be compatible
+ *                             with sanitize_key().
  * @param callable $function   The function to be called to output the content for this page.
  * @param string   $icon_url   The URL to the icon to be used for this menu.
  *                             * Pass a base64-encoded SVG using a data URI, which will be colored to match
@@ -1126,11 +1128,15 @@ function add_menu_page( $page_title, $menu_title, $capability, $menu_slug, $func
  * @global array $_registered_pages
  * @global array $_parent_pages
  *
- * @param string   $parent_slug The slug name for the parent menu (or the file name of a standard WordPress admin page).
- * @param string   $page_title  The text to be displayed in the title tags of the page when the menu is selected.
+ * @param string   $parent_slug The slug name for the parent menu (or the file name of a standard
+ *                              WordPress admin page).
+ * @param string   $page_title  The text to be displayed in the title tags of the page when the menu
+ *                              is selected.
  * @param string   $menu_title  The text to be used for the menu.
  * @param string   $capability  The capability required for this menu to be displayed to the user.
- * @param string   $menu_slug   The slug name to refer to this menu by (should be unique for this menu).
+ * @param string   $menu_slug   The slug name to refer to this menu by. Should be unique for this menu
+ *                              and only include lowercase alphanumeric, dashes, and underscores characters
+ *                              to be compatible with sanitize_key().
  * @param callable $function    The function to be called to output the content for this page.
  * @return false|string The resulting page's hook_suffix, or false if the user does not have the capability required.
  */
diff --git a/wp-admin/includes/template.php b/wp-admin/includes/template.php
index 87236d4846..32cdc0214e 100644
--- a/wp-admin/includes/template.php
+++ b/wp-admin/includes/template.php
@@ -892,7 +892,10 @@ function wp_import_upload_form( $action ) {
  * @param string|array|WP_Screen $screen        Optional. The screen or screens on which to show the box
  *                                              (such as a post type, 'link', or 'comment'). Accepts a single
  *                                              screen ID, WP_Screen object, or array of screen IDs. Default
- *                                              is the current screen.
+ *                                              is the current screen.  If you have used add_menu_page() or 
+ *                                              add_submenu_page() to create a new screen (and hence screen_id),
+ *                                              make sure your menu slug conforms to the limits of sanitize_key()
+ *                                              otherwise the 'screen' menu may not correctly render on your page.
  * @param string                 $context       Optional. The context within the screen where the boxes
  *                                              should display. Available contexts vary from screen to
  *                                              screen. Post edit screen contexts include 'normal', 'side',
@@ -987,7 +990,11 @@ function add_meta_box( $id, $title, $callback, $screen = null, $context = 'advan
  * @global array $wp_meta_boxes
  *
  * @staticvar bool $already_sorted
- * @param string|WP_Screen $screen  Screen identifier
+ *
+ * @param string|WP_Screen $screen  Screen identifier. If you have used add_menu_page() or
+ *                                  add_submenu_page() to create a new screen (and hence screen_id)
+ *                                  make sure your menu slug conforms to the limits of sanitize_key()
+ *                                  otherwise the 'screen' menu may not correctly render on your page.
  * @param string           $context box context
  * @param mixed            $object  gets passed to the box callback function as first parameter
  * @return int number of meta_boxes
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 5c65195920..37594021a3 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-alpha-40966';
+$wp_version = '4.9-alpha-40967';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.