Function save_through 

pub fn save_through<S: Storage, T: Storage>(
    source: &S,
    at: Rev,
    to: T,
    clock: Clock,
    by: &Identity,
) -> Result<Store<T>, PrefixFailure>

Write the document as it stood at at into a new container at to, and open it.

The head of the new history is at, so the session that lands in it is writable at the rev it was looking at — which is the whole point.

Errors

PrefixFailure: the source manifest could not be read or does not hold at, the container could not be laid out, revs or artwork the prefix names could not be carried over, or the projection did not land.