this is a spreadsheet ml2003 and not supporting it is not a big deal since this format is probably not widely used in the wild. Basically this file should need

this is a spreadsheet ml2003 and not supporting it is not a big deal since this format is probably not widely used in the wild. Basically this file should need a .xml file format, but excel will read files with .xls as well (besides that this is not correct). Basically the XLS was/is a binary format and XLSX is the new spreadsheet ml 2007+ syntax that is standardised. (edit: well the good part of the xml-files were that they could be streamed. this is / was huge for data processing and exporting a la csv)