Chat identifier.
A draft of a message in the topic; may be null if none.
Forum topic identifier of the topic.
Optional is_True, if the topic is pinned in the topic list.
Identifier of the last read incoming message.
Identifier of the last read outgoing message.
Notification settings for the topic.
Number of unread messages with a mention/reply in the topic.
Number of messages with unread reactions in the topic.
Information about a topic in a forum chat was changed. Subtype of Update.