http-stats:
HTTP/1.1 Public-Extension header field

Common Public-Extension header values:

Public-Extension: http://schemas.microsoft.com/repl-2

Sample Public-Extension web server response:

HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
Content-Length: 4159
Public-Extension: http://schemas.microsoft.com/repl-2
Date: Fri, 30 Jul 2010 17:04:51 +0000

<!DOCTYPE html PUBLIC "-//W3C//DTD ...
...
...

Other common HTTP headers

Other less common headers