public function setBarcode($text_, $alternativeText_ = null, Io_Charset $charset_ = null, $type_ = self::TYPE_BARCODE_2DMATRIX_QR)
 {
     if (null === $charset_) {
         $charset_ = Io_Charset::ISO_8859_1();
     }
     $barcode = array('format' => $type_, 'message' => $text_, 'messageEncoding' => strtolower($charset_->name()));
     if (null !== $alternativeText_) {
         $barcode['altText'] = $alternativeText_;
     }
     $this->properties->barcode = $barcode;
 }