Dan Fraticiu

<?php

class Nfr_Menu_Walker extends Walker_Nav_Menu{

        /**
     * Traverse elements to create list from elements.
     *
     * Display one element if the element doesn't have any children otherwise,
     * display the element and its children. Will only traverse up to the max
     * depth and no ignore elements under that depth. It is possible to set the
     * max depth to include all depths, see walk() method.
     *
     * This method shouldn't be called directly, use the walk() method instead.
     *
     * @since 2.5.0
     *
     * @param object $element Data object
     * @param array $children_elements List of elements to continue traversing.
     * @param int $max_depth Max depth to traverse.
     * @param int $depth Depth of current element.
     * @param array $args
     * @param string $output Passed by reference. Used to append additional content.
     * @return null Null on failure with no changes to parameters.
     */
    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');

        $cb_args = array_merge( array(&$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);
    }
}