Backcountry theme - subnav descriptions

subnav-descriptions.php

<?php
/** Add description to secondary navigation */
add_filter( 'walker_nav_menu_start_el', 'add_description', 10, 4 ); 
function add_description( $item_output, $item, $depth, $args ) {

	$args = (array) $args;
       
	if ( $args['theme_location'] != 'primary' )  {
		return preg_replace( '/(<a.*?>[^<]*?)</', '$1' . "<span class=\"menu-description\">{$item->post_content}</span><", $item_output ); 
	} else {
		return $item_output;
	}
}