Part of bzrlib
| Class | Revision | Single revision on a branch. |
| Function | iter_ancestors | Undocumented |
| Function | find_present_ancestors | Return the ancestors of a revision present in a branch. |
| Function | is_reserved_id | Determine whether a revision id is reserved |
| Function | check_not_reserved_id | Raise ReservedId if the supplied revision_id is reserved |
| Function | ensure_null | Ensure only NULL_REVISION is used to represent the null revision |
| Function | is_null | Undocumented |
| Function | __get_closest | Undocumented |
It's possible that a branch won't have the complete ancestry of one of its revisions.