I think it would be good to enhance the documentation on what syntactical constraints there are on keys.
- what character range is allowed? what about control characters?
- is leading or trailing whitespace allowed?
- are there any assumptions about Unicode normalization on lookup?
- are keys opaque strings? for instance, does the "/" character have any special role? will all keys have the "n:" prefix?
- what length needs to be supported? (MySQL has a limit on 767/4 characters because of UTF8-to-octet mapping)