Source

File: wp-admin/includes/nav-menu.php

function wp_save_nav_menu_items( $menu_id = 0, $menu_data = array() ) {
	$menu_id     = (int) $menu_id;
	$items_saved = array();

	if ( 0 == $menu_id || is_nav_menu( $menu_id ) ) {

		// Loop through all the menu items' POST values.
		foreach ( (array) $menu_data as $_possible_db_id => $_item_object_data ) {
			if (
				// Checkbox is not checked.
				empty( $_item_object_data['menu-item-object-id'] ) &&
				(
					// And item type either isn't set.
					! isset( $_item_object_data['menu-item-type'] ) ||
					// Or URL is the default.
					in_array( $_item_object_data['menu-item-url'], array( 'https://', 'http://', '' ), true ) ||
					// Or it's not a custom menu item (but not the custom home page).
					! ( 'custom' === $_item_object_data['menu-item-type'] && ! isset( $_item_object_data['menu-item-db-id'] ) ) ||
					// Or it *is* a custom menu item that already exists.
					! empty( $_item_object_data['menu-item-db-id'] )
				)
			) {
				// Then this potential menu item is not getting added to this menu.
				continue;
			}

			// If this possible menu item doesn't actually have a menu database ID yet.
			if (
				empty( $_item_object_data['menu-item-db-id'] ) ||
				( 0 > $_possible_db_id ) ||
				$_possible_db_id != $_item_object_data['menu-item-db-id']
			) {
				$_actual_db_id = 0;
			} else {
				$_actual_db_id = (int) $_item_object_data['menu-item-db-id'];
			}

			$args = array(
				'menu-item-db-id'       => ( isset( $_item_object_data['menu-item-db-id'] ) ? $_item_object_data['menu-item-db-id'] : '' ),
				'menu-item-object-id'   => ( isset( $_item_object_data['menu-item-object-id'] ) ? $_item_object_data['menu-item-object-id'] : '' ),
				'menu-item-object'      => ( isset( $_item_object_data['menu-item-object'] ) ? $_item_object_data['menu-item-object'] : '' ),
				'menu-item-parent-id'   => ( isset( $_item_object_data['menu-item-parent-id'] ) ? $_item_object_data['menu-item-parent-id'] : '' ),
				'menu-item-position'    => ( isset( $_item_object_data['menu-item-position'] ) ? $_item_object_data['menu-item-position'] : '' ),
				'menu-item-type'        => ( isset( $_item_object_data['menu-item-type'] ) ? $_item_object_data['menu-item-type'] : '' ),
				'menu-item-title'       => ( isset( $_item_object_data['menu-item-title'] ) ? $_item_object_data['menu-item-title'] : '' ),
				'menu-item-url'         => ( isset( $_item_object_data['menu-item-url'] ) ? $_item_object_data['menu-item-url'] : '' ),
				'menu-item-description' => ( isset( $_item_object_data['menu-item-description'] ) ? $_item_object_data['menu-item-description'] : '' ),
				'menu-item-attr-title'  => ( isset( $_item_object_data['menu-item-attr-title'] ) ? $_item_object_data['menu-item-attr-title'] : '' ),
				'menu-item-target'      => ( isset( $_item_object_data['menu-item-target'] ) ? $_item_object_data['menu-item-target'] : '' ),
				'menu-item-classes'     => ( isset( $_item_object_data['menu-item-classes'] ) ? $_item_object_data['menu-item-classes'] : '' ),
				'menu-item-xfn'         => ( isset( $_item_object_data['menu-item-xfn'] ) ? $_item_object_data['menu-item-xfn'] : '' ),
			);

			$items_saved[] = wp_update_nav_menu_item( $menu_id, $_actual_db_id, $args );

		}
	}
	return $items_saved;
}