在XML文件中存储XML数据的最佳方法是什么

I am looking for a way to store XML data in an Excel file. The data should be completely hidden to the user, it should not be in a cell or comment, even hidden. Also, the data should be preserved when the user opens and then saves the file with Excel. I am not looking for a way to map cells to external XML data. The XML data should be inside the xlsx file.I am looking for a way to store XML data in an