/**
  * @param Workflow $workflow
  * @param User $user
  * @param string $content
  * @param string $format wikitext|html
  * @param string[optional] $changeType
  * @return PostRevision
  */
 public function reply(Workflow $workflow, User $user, $content, $format, $changeType = 'reply')
 {
     $reply = new self();
     // UUIDs should not be reused for different entities/entity types in the future.
     // (It is also inconsistent with newFromId, which uses separate ones.)
     // This may be changed here in the future.
     $reply->revId = $reply->postId = UUID::create();
     $reply->user = UserTuple::newFromUser($user);
     $reply->origUser = $reply->user;
     $reply->replyToId = $this->postId;
     $reply->setContent($content, $format, $workflow->getArticleTitle());
     $reply->changeType = $changeType;
     $reply->setChildren(array());
     $reply->setDepth($this->getDepth() + 1);
     $reply->rootPost = $this->rootPost;
     return $reply;
 }