function knaeckebrot_nav_menu_link_attributes( $atts, $item, $args, $depth ) {
// Add [aria-haspopup] and [aria-expanded] to menu items that have children
$item_has_children = in_array( 'menu-item-has-children', $item->classes );
if ( $item_has_children ) {
$atts['aria-haspopup'] = "true";
$atts['aria-expanded'] = "false";
}
return $atts;
}
add_filter( 'nav_menu_link_attributes', 'knaeckebrot_nav_menu_link_attributes', 10, 4 );