/// `Unsize` is implemented for:
///
/// - `[T; N]` is `Unsize<[T]>`
-/// - `T` is `Unsize<Trait>` when `T: Trait`
+/// - `T` is `Unsize<dyn Trait>` when `T: Trait`
/// - `Foo<..., T, ...>` is `Unsize<Foo<..., U, ...>>` if:
/// - `T: Unsize<U>`
/// - Foo is a struct