We want to prefer the newer/versioned formulae when possible but this
is preferable to a random cached formula or, worse, no formula.
This means `brew info foo` will never complain that `foo` is a missing
formula.
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.