ReadonlyAnchorThe anchor; null when there is none.
ReadonlyForkThe Sequence of the anchor; null when the replaced message is the first one (nothing is inherited).
ReadonlyKindReadonlyParentThe branch of the anchor; null is Main.
Optional ReadonlySourceThe author of the replaced message, read as the draft opens: the draft's window ends before that message.
ReadonlySourceThe replaced message; the new fork's SourceDetailID, so its chip shows under that message.
A new fork that replaces a message (Fork from here): shown like a fork, created on the first send. It starts at the row before the replaced message on its path (the anchor).