Menu Walker with Parent Marking

walker.php

class Walker_Header extends Walker_Nav_Menu {
	/**
	 * @see Walker::$tree_type
	 * @since 3.0.0
	 * @var string
	 */
	var $tree_type = array( 'post_type', 'taxonomy', 'custom' );

	/**
	 * @see Walker::$db_fields
	 * @since 3.0.0
	 * @todo Decouple this.
	 * @var array
	 */
	var $db_fields = array( 'parent' => 'menu_item_parent', 'id' => 'db_id' );

        function display_element( $element, &$children_elements, $max_depth, $depth=0, $args, &$output ) {

		if ( !$element )
			return;

		$id_field = $this->db_fields['id'];

		//display this element
		if ( is_array( $args[0] ) )
			$args[0]['has_children'] = ! empty( $children_elements[$element->$id_field] );
		
		//Adds the 'parent' class to the current item if it has children		
		if( ! empty( $children_elements[$element->$id_field] ) )
			array_push($element->classes,'parent'. $depth);
		
		$cb_args = array_merge( array(&$output, $element, $depth), $args);
		
		call_user_func_array(array(&$this, 'start_el'), $cb_args);

		$id = $element->$id_field;

		// descend only when the depth is right and there are childrens for this element
		if ( ($max_depth == 0 || $max_depth > $depth+1 ) && isset( $children_elements[$id]) ) {

			foreach( $children_elements[ $id ] as $child ){

				if ( !isset($newlevel) ) {
					$newlevel = true;
					//start the child delimiter
					$cb_args = array_merge( array(&$output, $depth), $args);
					call_user_func_array(array(&$this, 'start_lvl'), $cb_args);
				}
				$this->display_element( $child, $children_elements, $max_depth, $depth + 1, $args, $output );
			}
			unset( $children_elements[ $id ] );
		}

		if ( isset($newlevel) && $newlevel ){
			//end the child delimiter
			$cb_args = array_merge( array(&$output, $depth), $args);
			call_user_func_array(array(&$this, 'end_lvl'), $cb_args);
		}

		//end this element
		$cb_args = array_merge( array(&$output, $element, $depth), $args);
		call_user_func_array(array(&$this, 'end_el'), $cb_args);
	}
        
	/**
	 * @see Walker::start_lvl()
	 * @since 3.0.0
	 *
	 * @param string $output Passed by reference. Used to append additional content.
	 * @param int $depth Depth of page. Used for padding.
	 */
	function start_lvl(&$output, $depth) {
		$indent = str_repeat("\t", $depth);
		$output .= "\n$indent<ul class=\"sub-menu\">\n";
	}

	/**
	 * @see Walker::end_lvl()
	 * @since 3.0.0
	 *
	 * @param string $output Passed by reference. Used to append additional content.
	 * @param int $depth Depth of page. Used for padding.
	 */
	function end_lvl(&$output, $depth) {
		$indent = str_repeat("\t", $depth);
		$output .= "$indent</ul>\n";
	}

	/**
	 * @see Walker::start_el()
	 * @since 3.0.0
	 *
	 * @param string $output Passed by reference. Used to append additional content.
	 * @param object $item Menu item data object.
	 * @param int $depth Depth of menu item. Used for padding.
	 * @param int $current_page Menu item ID.
	 * @param object $args
	 */
        
	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;
		$classes[] = 'menu-item-' . $item->ID;

		$class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item, $args ) );
		$class_names = ' class="' . esc_attr( $class_names ) . '"';

		$id = apply_filters( 'nav_menu_item_id', 'menu-item-'. $item->ID, $item, $args );
		$id = strlen( $id ) ? ' id="' . esc_attr( $id ) . '"' : '';

		$output .= $indent . '<li' . $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 .= '</a>';
		$item_output .= $args->after;

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

	/**
	 * @see Walker::end_el()
	 * @since 3.0.0
	 *
	 * @param string $output Passed by reference. Used to append additional content.
	 * @param object $item Page data object. Not used.
	 * @param int $depth Depth of page. Not Used.
	 */
	function end_el(&$output, $item, $depth) {
		$output .= "</li>\n";
	}
}