The linkage information the binary needs to use the library `foo`.
- But like `use`, all `extern mod` statements that refer to the same library are interchangeable,
- as each one really just presents an alias to an external module (the crate root of the library your linking against).
+ as each one really just presents an alias to an external module (the crate root of the library
+ you're linking against).
Remember how `use`-statements have to go before local declarations because the latter shadows the former?
Well, `extern mod` statements also have their own rules in that regard: