locations_nonce.php

<?php
// From wp-admin/nav-menus.php

		break;
	case 'locations':
		check_admin_referer( 'save-menu-locations', 'save-menu-locations-nonce', false );

		// Get existing menu locations assignments
		$locations = get_registered_nav_menus();
		$menu_locations = get_nav_menu_locations();

		// Merge new and existing menu locations if any new ones are set
		if ( isset( $_POST['menu-locations'] ) ) {
			$new_menu_locations = array_map( 'absint', $_POST['menu-locations'] );
			$menu_locations = array_merge( $menu_locations, $new_menu_locations );
			// Set menu locations
			set_theme_mod( 'nav_menu_locations', $menu_locations );
		}
		// TODO: Add a message

		break;