Index: wp-includes/nav-menu-template.php
===================================================================
--- wp-includes/nav-menu-template.php	(revision 14604)
+++ wp-includes/nav-menu-template.php	(working copy)
@@ -192,7 +192,7 @@
 function wp_nav_menu( $args = array() ) {
 	$defaults = array( 'menu' => '', 'container' => 'div', 'container_class' => '', 'menu_class' => 'menu', 'echo' => true,
 	'fallback_cb' => 'wp_page_menu', 'before' => '', 'after' => '', 'link_before' => '', 'link_after' => '',
-	'depth' => 0, 'walker' => '', 'context' => 'frontend' );
+	'depth' => 0, 'walker' => '', 'context' => 'frontend', 'slot' => '' );
 
 	$args = wp_parse_args( $args, $defaults );
 	$args = apply_filters( 'wp_nav_menu_args', $args );
@@ -201,6 +201,12 @@
 	// Get the nav menu
 	$menu = wp_get_nav_menu_object( $args->menu );
 
+	if ( ! $menu && $slot ) {
+		$slots = get_option('nav_menu_slots');
+		if ( isset($slots) && isset($slots[$slot]) )
+			$menu = wp_get_nav_menu_object( $slots['slot'] );
+	}
+
 	// If we couldn't find a menu based off the menu argument 
 	// get the first menu that has items.
 	if ( ! $menu ) {
Index: wp-includes/nav-menu.php
===================================================================
--- wp-includes/nav-menu.php	(revision 14604)
+++ wp-includes/nav-menu.php	(working copy)
@@ -62,6 +62,21 @@
 }
 
 /**
+ * Register nav menus for a theme.
+ *
+ * @since 3.0.0
+ *
+ * @param array Associative array of menu slot identifiers and descriptions.
+ */
+function register_nav_menus( $menus = array() ) {
+	global $_wp_registered_nav_menus;
+
+	add_theme_support( 'nav-menus' );
+
+	$_wp_registered_nav_menus = $menus;
+}
+
+/**
  * Determine whether the given ID is a nav menu item.
  *
  * @since 3.0.0