<!-- Constraints -->
* `T: U`: generic parameter `T` constrained to types that implement `U`. See [Traits].
-* `T: 'a`: generic type `T` must outlive lifetime `'a`.
+* `T: 'a`: generic type `T` must outlive lifetime `'a`. When we say that a type 'outlives' the lifetime, we mean that it cannot transitively contain any references with lifetimes shorter than `'a`.
+* `T : 'static`: The generic type `T` contains no borrowed references other than `'static` ones.
* `'b: 'a`: generic lifetime `'b` must outlive lifetime `'a`.
* `T: ?Sized`: allow generic type parameter to be a dynamically-sized type. See [Unsized Types (`?Sized`)].
* `'a + trait`, `trait + trait`: compound type constraint. See [Traits (Multiple Trait Bounds)].