Menu Walker per la personalizzazione del menu_nav https://code.tutsplus.com/tutorials/function-examination-wp_nav_menu--wp-25525
// FUNCTION
class description_walker extends Walker_Nav_Menu {
function start_el(&$output, $item, $depth, $args) {
global $wp_query;
$indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';
$class_names = $value = '';
$classes = empty( $item->classes ) ? array() : (array) $item->classes;
$class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) );
$class_names = ' class="'. esc_attr( $class_names ) . '"';
$output .= $indent . '<li id="menu-item-'. $item->ID . '"' . $value . $class_names .'>';
$attributes = ! empty( $item->attr_title ) ? ' title="' . esc_attr( $item->attr_title ) .'"' : '';
$attributes .= ! empty( $item->target ) ? ' target="' . esc_attr( $item->target ) .'"' : '';
$attributes .= ! empty( $item->xfn ) ? ' rel="' . esc_attr( $item->xfn ) .'"' : '';
$attributes .= ! empty( $item->url ) ? ' href="' . esc_attr( $item->url ) .'"' : '';
$description = ! empty( $item->description ) ? '<span>'.esc_attr( $item->description ).'</span>' : '';
if($depth != 0) {
$description = $append = $prepend = "";
}
$item_output = $args->before;
$item_output .= '<a itemprop="url"'. $attributes .'>';
$item_output .= $args->link_before .apply_filters( 'the_title', $item->title, $item->ID );
$item_output .= $description.$args->link_after;
$item_output .= '</a>';
$item_output .= $args->after;
$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
}
}
// TEMA
wp_nav_menu( array( 'walker' => new description_walker(), 'link_before' => '<span itemprop="name">', 'link_after' => '</span>', 'items_wrap' => '<nav class="nav-primary" role="navigation" itemscope="itemscope" itemtype="http://schema.org/SiteNavigationElement"><ul id="%1$s" class="%2$s">%3$s</ul></nav>') );