private function _writeBoundsheet($sheet, $offset)
	{
		$sheetname = $sheet->getTitle();
		$record    = 0x0085;                    // Record identifier

		// sheet state
		switch ($sheet->getSheetState()) {
			case PHPExcel_Worksheet::SHEETSTATE_VISIBLE:	$ss = 0x00; break;
			case PHPExcel_Worksheet::SHEETSTATE_HIDDEN:		$ss = 0x01; break;
			case PHPExcel_Worksheet::SHEETSTATE_VERYHIDDEN:	$ss = 0x02; break;
			default: $ss = 0x00; break;
		}

		// sheet type
		$st = 0x00;

		$grbit     = 0x0000;                    // Visibility and sheet type

		$data      = pack("VCC", $offset, $ss, $st);
		$data .= PHPExcel_Shared_String::UTF8toBIFF8UnicodeShort($sheetname);

		$length = strlen($data);
		$header = pack("vv",  $record, $length);
		$this->_append($header . $data);
	}