When the following PHP script:

<?php
ob_start("ob_gzhandler");
ob_end_clean();
print "foo!\n";
?>

is called from a client that sends "Accept-encoding: gzip", it produces the following result:

-----------------------
HTTP/1.1 200 OK
Date: Fri, 13 Sep 2002 13:53:34 GMT
Server: Apache/1.3.26 (Unix) PHP/4.2.3 mod_ssl/2.8.10 OpenSSL/0.9.6e
X-Powered-By: PHP/4.2.3
Content-Encoding: gzip
Vary: Accept-Encoding
Content-Length: 26
Content-Type: text/html

foo!
-----------------------

The output is not gzip'ed, but the header still indicates that it is.