obtest.php

<?php
/*
TESTED:

CentOS/WHM/CPanel
Apache 2.4
PHP 5.5.29
suPHP
CGI/FastCGI

AND

Debian
Lighttpd 1.4.31
PHP 5.4.45
FPM/FastCGI

*/

if (!ob_start(null, 0, PHP_OUTPUT_HANDLER_CLEANABLE)) echo 'could not open output buffer...';

//TODO: include 'somecontent.php';
echo 'some content that shouln\'t be seen because it gets extracted from the buffer into a variable...';

//ORIGINALLY USING THIS, BUT HID THE FAILURE OF ob_end_clean BELOW: $html = ob_get_clean();

$html = ob_get_contents();
if (!ob_end_clean()) echo 'could not clean output buffer...';

echo 'script finished...';

//RESULT: some content that shouln't be seen because it gets extracted from the buffer into a variable...could not clean output buffer...script finished...