ReadonlyauthorWho made it, when the stack knows ('user', 'agent', 'macro', or a collaborator). null when
it does not.
ReadonlydescriptionWhat the entry did. May be a message key; resolve it for display (t() passes plain text through).
ReadonlymetaWhat was recorded with the entry — command is the key of the command that made it, when one did.
One entry of the undo or redo stack, as a view shows it.