Add '_ to LIFETIME_OR_LABEL

Author: ehuss

src/expressions/loop-expr.md

@@ -209,6 +209,8 @@ Labels follow the hygiene and shadowing rules of local variables. For example, t
 }
 ```
 
+`'_` is not a valid loop label.
+
 ## `break` expressions
 
 > **<sup>Syntax</sup>**\

src/items/generics.md

@@ -44,6 +44,8 @@ See [generic parameter scopes] for more details.
 [function pointers] have lifetime or type parameters as well, but are not
 referred to with path syntax.
 
+`'_` is not a valid lifetime parameter.
+
 ### Const generics
 
 *Const generic parameters* allow items to be generic over constant values. The

src/tokens.md

@@ -645,6 +645,8 @@ Examples of reserved forms:
 >
 > LIFETIME_OR_LABEL :\
 >       `'` [NON_KEYWORD_IDENTIFIER][identifier]
+>   _(not immediately followed by `'`)_\
+>    | `'_`
 >   _(not immediately followed by `'`)_
 
 Lifetime parameters and [loop labels] use LIFETIME_OR_LABEL tokens. Any

src/trait-bounds.md

@@ -18,8 +18,7 @@
 >
 > _Lifetime_ :\
 >       [LIFETIME_OR_LABEL]\
->    | `'static`\
->    | `'_`
+>    | `'static`
 
 [Trait] and lifetime bounds provide a way for [generic items][generic] to
 restrict which types and lifetimes are used as their parameters. Bounds can be