What is a pur autre vie life estate?

It endures over the lifetime of the owner, then passes to an heir

It ends with the death of the life estate owner and may pass back to the original owners or their heirs or to a named third party

It ends with the death of the original grantor, then passes to a third party

It endures over the lifetime of a third person, after which the property passes from the tenant holder to the original grantor