The tooling helps a lot. If you do use something that's behind a feature gate, you'll find out in real time in your IDE, and from there you can either automatically insert the feature or you can immediately choose to use a different method. You won't have to deal with it an hour later when you've already used it in 6 places, or something like that. I haven't found it to be a big problem, personally.

The API documentation of the central data types (Option, Result, Vec, etc) is more of less your toolkit, and they're pretty cohesive (eg they all have a `map()` method, Result and Option both have an `or()` method, etc).

Spec would be excellent, of course.