I am looking to export data from members to csv/xlsx. The method I am looking at is to use PHP to write the header as csv/text allowing the user to click and download. This downloads the full html, so I am looking to stop all of that data. Do I need to create a blank theme to do this, or is there a simpler way?

I did similar for printing, but simply hid everything unneeded with the print css. This would still download the code though, right?