Source

File: wp-admin/includes/export.php

function wxr_nav_menu_terms() {
		$nav_menus = wp_get_nav_menus();
		if ( empty( $nav_menus ) || ! is_array( $nav_menus ) ) {
			return;
		}

		foreach ( $nav_menus as $menu ) {
			echo "\t<wp:term>";
			echo '<wp:term_id>' . intval( $menu->term_id ) . '</wp:term_id>';
			echo '<wp:term_taxonomy>nav_menu</wp:term_taxonomy>';
			echo '<wp:term_slug>' . wxr_cdata( $menu->slug ) . '</wp:term_slug>';
			wxr_term_name( $menu );
			echo "</wp:term>\n";
		}
	}