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<?php namespace PhpOffice\PhpSpreadsheet\Writer\Ods;< use PhpOffice\PhpSpreadsheet\Spreadsheet; <class Thumbnails extends WriterPart { /** * Write Thumbnails/thumbnail.png to PNG format. *< * @param Spreadsheet $spreadsheet < ** @return string XML Output */< public function writeThumbnail(Spreadsheet $spreadsheet = null)> public function write(): string{ return ''; } }