I know I can edit the items within the wp_nav_menu by declaring a custom walker, but I want to add some code just inside the container, which isn't handled by a walker.
It's in nav-menu-menu-template.php, so I can get the desired effect by adding my code after line 329...
$nav_menu .= "<div class='topper'> <a href='".get_home_url()."' class='intranet'>H</a> </div>";
...but of course this will disappear on an update. What hook do I need to achieve the same?