A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Rather than using Save As > Excel 2004 XML Spreadsheet (.xml), maybe if you choose the default save as Excel (.xlsx) format you'd be better off.
You can change the file extension of a (.xlsx) file to (.zip) in Finder. Then, also in Finder, double-click the Zip file to expose the folder structure of the Office Open XML file. You can get at the text of the XML files that way.