This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
The lack of ".php" in this URI adds three HTTP response headers: Content-Location: pfloats.php Vary: negotiate TCN: choice This causes the following error message from the CSS Validator: I/O Error: http://simple.be/test/valid/pfile: Not Acceptable The XHTML 1.1 validates, and other (.html) variations of the URI (with the exact same XHTML/CSS files) pass CSS validation. I have not narrowed it down to exactly which HTTP header causes the error. I'm hoping you that I have provided enough info. Links to all 4 URL combinations are at the listed URL. Thanks, Brett Hamilton
Corrections: These three HTTP headers: Content-Location: pfile.php Vary: negotiate TCN: choice and I intended to specify Component: "media type"
The problem is actually slightly different from what you describe; your webserver is behaving inappropriately. See Bug 232 for more information. *** This bug has been marked as a duplicate of 232 ***