ob_gzhandler() is intended to be used as a callback
function for ob_start() to help facilitate sending
gz-encoded data to web browsers that support compressed web pages.
Before ob_gzhandler() actually sends compressed data,
it determines what type of content encoding the browser will accept
("gzip", "deflate" or none at all) and will return its output accordingly.
All browsers are supported since it's up to the browser to send the
correct header saying that it accepts compressed web pages. If a browser
doesn't support compressed pages this function returns
<p>This should be a compressed page.</p>