Excel export produces security warning from Excel

[unikitty37]

The XLS export button actually produces an HTML file with a .xls extension. This produces the following warning when loading into Excel:

While the file itself is safe to open, and can be saved as a normal Excel file, it would be better for the plugin to actually output a genuine .xls file, and to maybe have an HTML export button that could use the existing table generation code.

Failing that, an easier fix might be to have a note in the UI that Excel will give this warning, and that it's safe to allow the file to open 😀