> The R6RS library versioning was probably over-engineered because it
> also defines sub- and sub-subversions and so. Nevertheless, if we add
> versioning, we should (re-)use (a subset of) the R6RS versioning
> system to maintain the rough bijection we have between R7RS's
> define-library and R6RS library form. This makes it easy to move
> provide modules for both standards and for implementations to support
> both module standards. So it would be (scheme char (2020)). And
> (import (scheme char ((<= 2020))), or the like.

That sounds reasonable :)

Rust editions are something very similar to what we're talking about:

https://doc.rust-lang.org/edition-guide/editions/

https://doc.rust-lang.org/edition-guide/