WordPress at a glance
filter is not described

wp_nav_menu_items filter-hook . WP 3.0.0

Filters the HTML list content for navigation menus.

Usage

add_filter( 'wp_nav_menu_items', 'filter_function_name_5335', 10, 2 );
function filter_function_name_5335( $items, $args ){
	// filter...

	return $items;
}
$items(string)
The HTML list content for the menu items.
$args(stdClass)
An object containing wp_nav_menu() arguments.

Where the hook is called

wp_nav_menu()
wp-includes/nav-menu-template.php 220
$items = apply_filters( 'wp_nav_menu_items', $items, $args );

Where the hook is used (in WP core)

Does not used.