public function open( $attributes = array() ) {
        $this->setAttributes( $attributes );
        $html = '<' . $this->tagName
                    . $this->renderAttributes()
                    ;
        // should we close it ?
        if( $this->closeEmpty || $this->hasChildren() ) {
            $html .= '>';
        } else {
            $html .= '/>';
        }
        return $html;
    }