title: PHP Microsoft Excel file generation / export class
body: <p>I've been looking for a good Excel file generation class and have yet to find one - my number one issue is that I although I can get the exported file to open in Excel (running 2007), I always get a warning saying "the file is in a different format to the file extension".</p>
  
  <p>I noticed that the Excel export in phpMyAdmin even generates the aforementioned warning message.</p>
  
  <p>What code do other users use for this common requirement?</p>
  
  <p><strong>Quick update</strong> If I set the file extension of my generated Excel file as xml it opens in the browser (even though I'm sending the correct headers), but if I choose to save the xml file and then open it from Excel, it works without any warnings! Unfortunately, that's more hassle for the users than simply clicking 'Proceed anyway' with the warning I'm getting. Any more ideas?</p>