Incorrect code snippets / feature description (?)

Hey,
code snippet within `scope/borrow/alias.md` is completely valid & compiles after uncommenting line 22 `//let mutable_borrow = &mut point`.

I'd love to fix it but currently I'm still struggling to get a grasp on a language. As far as I understand it is acceptable to _have_ both many immutable and mutable references within the same scope but not to.. _use_ them in a interleaved manner?