This avoids `brew style` and friends from getting upset when they
attempt to use the native gem extensions from a previous portable Ruby
or a system Ruby.
ABI? What's that?
This is the (partially) documented public API for Homebrew.
The main class you should look at is the {Formula} class (and classes linked from there). That's the class that's used to create Homebrew formulae (i.e. package descriptions). Assume anything else you stumble upon is private.