tweak enclosing scope discussion

Author: RalfJung

promotion.md

@@ -78,7 +78,7 @@ the only difference.
 
 ## Promotion in const contexts
 
-When promoting inside a const context (`const` and `static` items and `const fn`), we relax almost all promotion restrictions, except for basic constness restrictions (such as interior mutability or `Drop`).
+When promoting inside a const context (`const` and `static` items and `const fn`), we relax almost all promotion restrictions, except for basic constness restrictions listed below.
 We do this for all kinds of promotion.
 
 For `const fn`, [this is a bug](https://github.com/rust-lang/rust/issues/75586).
@@ -101,7 +101,13 @@ the "enclosing scope", similar to how `let x = &mut x;` creates a reference
 whose lifetime lasts for the enclosing scope. This is decided during MIR
 building already, and does not involve lifetime extension.
 
-This is also sometimes called "outermost scope" rule.
+In contrast, this does not compile:
+
+```rust
+const OPT_EMPTY_BYTES: Option<&Vec<u8>> = Some(&Vec::new());
+```
+
+The "enclosing scope" rule only fires for outermost `&`, just like in `fn` bodies.
 
 ## Promotability