protected function _backtrackLoop()
    {
        $this->_popParent();

        if (!$this->_hasParents()) {
            return $this->_createIteration(null, null);
        }

        $parent  = &$this->_getCurrentIterable();
        $current = $this->_createCurrentIteration($parent);
        next($parent);

        if ($this->_isMode(R::MODE_CHILD_FIRST)) {
            return $current;
        }

        return $this->_loop();
    }