tokens.md: move the link reference definitions to the end of the file

Author: mattheww

src/tokens.md

@@ -430,8 +430,6 @@ Note that the Rust syntax considers `-1i8` as an application of the [unary minus
 operator] to an integer literal `1i8`, rather than
 a single integer literal.
 
-[unary minus operator]: expressions/operator-expr.md#negation-operators
-
 #### Tuple index
 
 > **<sup>Lexer</sup>**\
@@ -542,8 +540,6 @@ Lifetime parameters and [loop labels] use LIFETIME_OR_LABEL tokens. Any
 LIFETIME_TOKEN will be accepted by the lexer, and for example, can be used in
 macros.
 
-[loop labels]: expressions/loop-expr.md
-
 ## Punctuation
 
 Punctuation symbol tokens are listed here for completeness. Their individual
@@ -609,6 +605,41 @@ them are referred to as "token trees" in [macros].  The three types of brackets
 | `[` `]` | Square brackets |
 | `(` `)` | Parentheses     |
 
+## Reserved prefixes
+
+> **<sup>Lexer 2021+</sup>**\
+> RESERVED_TOKEN_DOUBLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b` or `r` or `br`_</sub> | `_` ) `"`\
+> RESERVED_TOKEN_SINGLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b`_</sub> | `_` ) `'`\
+> RESERVED_TOKEN_POUND : ( IDENTIFIER_OR_KEYWORD <sub>_Except `r` or `br`_</sub> | `_` ) `#`
+
+Some lexical forms known as _reserved prefixes_ are reserved for future use.
+
+Source input which would otherwise be lexically interpreted as a non-raw identifier (or a keyword or `_`) which is immediately followed by a `#`, `'`, or `"` character (without intervening whitespace) is identified as a reserved prefix.
+
+Note that raw identifiers, raw string literals, and raw byte string literals may contain a `#` character but are not interpreted as containing a reserved prefix.
+
+Similarly the `r`, `b`, and `br` prefixes used in raw string literals, byte literals, byte string literals, and raw byte string literals are not interpreted as reserved prefixes.
+
+> **Edition Differences**: Starting with the 2021 edition, reserved prefixes are reported as an error by the lexer (in particular, they cannot be passed to macros).
+>
+> Before the 2021 edition, a reserved prefixes are accepted by the lexer and interpreted as multiple tokens (for example, one token for the identifier or keyword, followed by a `#` token).
+>
+> Examples accepted in all editions:
+> ```rust
+> macro_rules! lexes {($($_:tt)*) => {}}
+> lexes!{a #foo}
+> lexes!{continue 'foo}
+> lexes!{match "..." {}}
+> lexes!{r#let#foo}         // three tokens: r#let # foo
+> ```
+>
+> Examples accepted before the 2021 edition but rejected later:
+> ```rust,edition2018
+> macro_rules! lexes {($($_:tt)*) => {}}
+> lexes!{a#foo}
+> lexes!{continue'foo}
+> lexes!{match"..." {}}
+> ```
 
 [Inferred types]: types/inferred.md
 [Range patterns]: patterns.md#range-patterns
@@ -636,6 +667,7 @@ them are referred to as "token trees" in [macros].  The three types of brackets
 [if let]: expressions/if-expr.md#if-let-expressions
 [keywords]: keywords.md
 [lazy-bool]: expressions/operator-expr.md#lazy-boolean-operators
+[loop labels]: expressions/loop-expr.md
 [machine types]: types/numeric.md
 [macros]: macros-by-example.md
 [match]: expressions/match-expr.md
@@ -656,42 +688,7 @@ them are referred to as "token trees" in [macros].  The three types of brackets
 [tuple structs]: items/structs.md
 [tuple variants]: items/enumerations.md
 [tuples]: types/tuple.md
+[unary minus operator]: expressions/operator-expr.md#negation-operators
 [use declarations]: items/use-declarations.md
 [use wildcards]: items/use-declarations.md
 [while let]: expressions/loop-expr.md#predicate-pattern-loops
-
-## Reserved prefixes
-
-> **<sup>Lexer 2021+</sup>**\
-> RESERVED_TOKEN_DOUBLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b` or `r` or `br`_</sub> | `_` ) `"`\
-> RESERVED_TOKEN_SINGLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b`_</sub> | `_` ) `'`\
-> RESERVED_TOKEN_POUND : ( IDENTIFIER_OR_KEYWORD <sub>_Except `r` or `br`_</sub> | `_` ) `#`
-
-Some lexical forms known as _reserved prefixes_ are reserved for future use.
-
-Source input which would otherwise be lexically interpreted as a non-raw identifier (or a keyword or `_`) which is immediately followed by a `#`, `'`, or `"` character (without intervening whitespace) is identified as a reserved prefix.
-
-Note that raw identifiers, raw string literals, and raw byte string literals may contain a `#` character but are not interpreted as containing a reserved prefix.
-
-Similarly the `r`, `b`, and `br` prefixes used in raw string literals, byte literals, byte string literals, and raw byte string literals are not interpreted as reserved prefixes.
-
-> **Edition Differences**: Starting with the 2021 edition, reserved prefixes are reported as an error by the lexer (in particular, they cannot be passed to macros).
->
-> Before the 2021 edition, a reserved prefixes are accepted by the lexer and interpreted as multiple tokens (for example, one token for the identifier or keyword, followed by a `#` token).
->
-> Examples accepted in all editions:
-> ```rust
-> macro_rules! lexes {($($_:tt)*) => {}}
-> lexes!{a #foo}
-> lexes!{continue 'foo}
-> lexes!{match "..." {}}
-> lexes!{r#let#foo}         // three tokens: r#let # foo
-> ```
->
-> Examples accepted before the 2021 edition but rejected later:
-> ```rust,edition2018
-> macro_rules! lexes {($($_:tt)*) => {}}
-> lexes!{a#foo}
-> lexes!{continue'foo}
-> lexes!{match"..." {}}
-> ```