<?php
function callback($string) {
	static $callback_invocations;
	$callback_invocations++;
	return "[callback:$callback_invocations]$string\n";
}

ob_start('callback', 0, false);

echo "Attempt to flush unerasable buffer - should fail... ";
var_dump(ob_flush());
// Check content of buffer after flush - if flush failed it should still contain the string above.
var_dump(ob_get_contents());
?>
