Output buffering

[CasEbb]

The docs for Streamed Responses mention "Internally, Laravel utilizes PHP's output buffering functionality." (https://laravel.com/docs/11.x/responses#streamed-responses). However, when I use the code example:

function streamedContent(): Generator {
    yield 'Hello, ';
    yield 'World!';
}
 
Route::get('/stream', function () {
    return response()->stream(function (): void {
        foreach (streamedContent() as $chunk) {
            echo $chunk;
            ob_flush();
            flush();
            sleep(2); // Simulate delay between chunks...
        }
    }, 200, ['X-Accel-Buffering' => 'no']);
});

It yields an ErrorException: ob_flush(): Failed to flush buffer. No buffer to flush. Apparently Laravel doesn't use output buffering? Setting a breakpoint on ob_start() with xdebug also doesn't trigger anything. Is it possible that the documentation here is wrong and Laravel relies on the output_buffering setting of php.ini and does not call ob_start() itself?