public static function startOutputBuffer()
    {
        if (ob_get_level() > 1) {
            return;
        }
        
        $outputCallback = null;
        if (GZIP_SUPPORTED && !DISABLE_GZIP) {
            $outputCallback = 'ob_gzhandler';
        }
        
        if (in_array($outputCallback, ob_list_handlers())) {
            return; // don't start same handler twice
        }
        
        ob_start($outputCallback);
    }