Call $ident:kind a macro matcher fragment specifier

In writing RFC 3531, I came to believe that the most correct fully
qualified term for what `kind` is in `$ident:kind` is a "macro matcher
fragment specifier", and I still think that's right.  It's unfortunate
that it's such a mouthful, but let's use that term in the syntax
index.

Author: traviscross

src/syntax-index.md

@@ -150,7 +150,7 @@ This appendix provides an index of tokens and common forms with links to where t
 |-------------------------------------------|-------|
 | `ident!(…)`<br>`ident!{…}`<br>`ident![…]` | [macro invocations] |
 | `$ident`                                  | [macro fragment substitution] |
-| `$ident:kind`                             | [macro fragment specifier] |
+| `$ident:kind`                             | [macro matcher fragment specifier] |
 | `$(…)…`                                   | [macro repetition] |
 
 ## Attributes
@@ -354,10 +354,10 @@ This appendix provides an index of tokens and common forms with links to where t
 [lifetimes and loop labels]: lex.token.life
 [literal patterns]: patterns.literal
 [macro calls]: macro.invocation
-[macro fragment specifier]: macro.decl.meta.specifier
 [macro fragment substitution]: macro.decl.meta.transcription
 [macro invocations]: macro.invocation
 [macro Kleene matcher]: macro.decl.repetition
+[macro matcher fragment specifier]: macro.decl.meta.specifier
 [macro repetition]: macro.decl.repetition
 [macros by example]: macro.decl
 [macros]: macro.decl