I don't like making this a separate module if it's not written in a way that's reusable by other classes. Either make it more generic or go back to making these class methods on `BasicEnvironment`.

If you go the more-generic route, move this into its own file under `lib/sass/util` and have some way to configure the parent (making it assume the existence of a `#parent` accessor is fine, I just don't like it assuming an instance variable).