- `put(string $data, string $reference)` saves data in `$data` to position `$reference`, or a new position if `$reference` is empty.
- `delete(string $reference)` delete data pointed by `$reference`
- `put(string $data, string $reference)` saves data in `$data` to position `$reference`, or a new position if `$reference` is empty.
- `delete(string $reference)` delete data pointed by `$reference`