Well, it doesn't mutate the `errors` variable. `errors = &mut someothervar;` would be illegal there. It dereferences a pointer (that itself is immutable, this d

Well, it doesn't mutate the `errors` variable. `errors = &mut someothervar;` would be illegal there. It dereferences a pointer (that itself is immutable, this doesn't matter as long as it's unique) to a mutable value and mutates that value, like it says on the tin.