Open XML was approved as a standard last December by ECMA International. The standards body then submitted the file format to the larger ISO standards organization in Geneva.

What to Know An XLSX file is a Microsoft Excel Open XML Format Spreadsheet file. Open one with Excel, Excel Viewer, Google Sheets, or another spreadsheet program.

Is Microsoft’s Open XML document standard “so complex and so geared towards compatibility with legacy Office compatibility that it could never be implemented as a fully functional file format ...