/**
* Callback for output handling.
*
* @param string|array $buffer
* @param int $flags
* @return string|array
*/
public function callback($buffer, $flags)
{
$marker = $this->opt & Output::IGNORE_MARKERS || is_array($buffer) ? null : Output::curMarker();
// Directly flush the output
if (!isset($marker)) {
return $this->transform->process($buffer);
}
// Keep caching the output of flush
$this->data[$marker] = $this->data;
return $flags & PHP_OUTPUT_HANDLER_END ? $this->transform->process($this->data) : null;
}