Update for "modern" meta matcher.

Author: ehuss

Diff for: src/attributes.md

@@ -86,8 +86,7 @@ fn some_unused_variables() {
 ## Meta Item Attribute Syntax
 
 A "meta item" is the syntax used for the _Attr_ rule by most [built-in
-attributes] and the [`meta` macro fragment specifier]. It has the following
-grammar:
+attributes]. It has the following grammar:
 
 > **<sup>Syntax</sup>**\
 > _MetaItem_ :\
@@ -268,7 +267,6 @@ The following is an index of all built-in attributes.
 [`link`]: items/external-blocks.md#the-link-attribute
 [`macro_export`]: macros-by-example.md#path-based-scope
 [`macro_use`]: macros-by-example.md#the-macro_use-attribute
-[`meta` macro fragment specifier]: macros-by-example.md
 [`must_use`]: attributes/diagnostics.md#the-must_use-attribute
 [`no_builtins`]: attributes/codegen.md#the-no_builtins-attribute
 [`no_implicit_prelude`]: items/modules.md#prelude-items

Diff for: src/macros-by-example.md

@@ -128,7 +128,7 @@ fragment specifiers are:
   * `ident`: an [IDENTIFIER_OR_KEYWORD]
   * `path`: a [_TypePath_] style path
   * `tt`: a [_TokenTree_] (a single [token] or tokens in matching delimiters `()`, `[]`, or `{}`)
-  * `meta`: a [_MetaItem_], the contents of an attribute
+  * `meta`: an [_Attr_], the contents of an attribute
   * `lifetime`: a [LIFETIME_TOKEN]
   * `vis`: a possibly empty [_Visibility_] qualifier
   * `literal`: matches `-`<sup>?</sup>[_LiteralExpression_]
@@ -477,12 +477,12 @@ For more detail, see the [formal specification].
 [LIFETIME_TOKEN]: tokens.md#lifetimes-and-loop-labels
 [Metavariables]: #metavariables
 [Repetitions]: #repetitions
+[_Attr_]: attributes.md
 [_BlockExpression_]: expressions/block-expr.md
 [_DelimTokenTree_]: macros.md
 [_Expression_]: expressions.md
 [_Item_]: items.md
 [_LiteralExpression_]: expressions/literal-expr.md
-[_MetaItem_]: attributes.md#meta-item-attribute-syntax
 [_MetaListIdents_]: attributes.md#meta-item-attribute-syntax
 [_Pattern_]: patterns.md
 [_Statement_]: statements.md