protected function elementClass(string $var_name = ''): string
    {
        if ($this->action) {
            return $this->s::restActionFormElementClass($var_name);
        } elseif ($this->cfg->Widget) {
            return $this->cfg->Widget->get_field_id($var_name);
        }
        return $this->cfg->slug.($var_name ? '-'.$this->c::nameToSlug($var_name) : '');
    }