public function and_(HTML_QuickForm2_Rule $next)
    {
        if ($next instanceof HTML_QuickForm2_Rule_Required) {
            throw new HTML_QuickForm2_InvalidArgumentException(
                'and_(): Cannot add a "required" rule'
            );
        }
        $this->chainedRules[count($this->chainedRules) - 1][] = $next;
        return $this;
    }