WordPress: Add menu item descriptions

<?php
/*
Go to Appearance » Menus. Click on Screen Options button at top right corner of the page. Check the Descriptions box.
(Vá até o menu Aparência » Menus. Clique sobre o botão Opções de Tela, no canto superior direito da página. Marque a opção Descrição)
*/

class Menu_Description 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 ) .'"' : '';

        $item_output = $args->before;
        $item_output .= '<a'. $attributes .'>';
        $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
        $item_output .= '<br /><span class="sub">' . $item->description . '</span>';
        $item_output .= '</a>';
        $item_output .= $args->after;

        $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
    }
}

/// Usage (como usar):
$walker = new Menu_Description;
wp_nav_menu( array( 'theme_location' => 'primary', 'menu_class' => 'nav-menu', 'walker' => $walker ) );


?>