This bit may require some more thought. The join string itself (on which the “join” method is called) may be a literal or a dynamic string, and this overload is valid only if it is a literal. But I don’t think we have a way to define a method overload only on `Literal[str]` and not on `str`? Maybe could use self-types or something for this, but it’s something that would require additional support I think. 

Carl