Clarify ManuallyDrop bit validity

library/core/src/mem/manually_drop.rs

@@ -4,12 +4,12 @@ use crate::ptr;
 /// A wrapper to inhibit compiler from automatically calling `T`’s destructor.
 /// This wrapper is 0-cost.
 ///
-/// `ManuallyDrop<T>` is guaranteed to have the same layout as `T`, and is subject
-/// to the same layout optimizations as `T`. As a consequence, it has *no effect*
-/// on the assumptions that the compiler makes about its contents. For example,
-/// initializing a `ManuallyDrop<&mut T>` with [`mem::zeroed`] is undefined
-/// behavior. If you need to handle uninitialized data, use [`MaybeUninit<T>`]
-/// instead.
+/// `ManuallyDrop<T>` is guaranteed to have the same layout and bit validity as
+/// `T`, and is subject to the same layout optimizations as `T`. As a consequence,
+/// it has *no effect* on the assumptions that the compiler makes about its
+/// contents. For example, initializing a `ManuallyDrop<&mut T>` with [`mem::zeroed`]
+/// is undefined behavior. If you need to handle uninitialized data, use
+/// [`MaybeUninit<T>`] instead.
 ///
 /// Note that accessing the value inside a `ManuallyDrop<T>` is safe.
 /// This means that a `ManuallyDrop<T>` whose content has been dropped must not