phorge-phorge/src/applications/maniphest/controller/ManiphestTaskDescriptionPreviewController.php

<?php

final class ManiphestTaskDescriptionPreviewController
  extends ManiphestController {

  public function processRequest() {
    $request = $this->getRequest();
    $description = $request->getStr('description');

    $task = new ManiphestTask();
    $task->setDescription($description);

    $output = PhabricatorMarkupEngine::renderOneObject(
      $task,
      ManiphestTask::MARKUP_FIELD_DESCRIPTION,
      $request->getUser());

    $content = phutil_tag_div('phabricator-remarkup', $output);

    return id(new AphrontAjaxResponse())
      ->setContent($content);
  }

}