Clean up docs for trigger_inclusion behaviour

Fixes #2775
Related:
 - #2834
 - #2832
 - #1762

Author: pirj

features/example_groups/shared_examples.feature

@@ -10,7 +10,6 @@ Feature: shared examples
   ```ruby
   include_examples "name"      # include the examples in the current context
   it_behaves_like "name"       # include the examples in a nested context
-  matching metadata            # include the examples in the current context
   ```
 
   **WARNING:** Files containing shared groups must be loaded before the files that

lib/rspec/core/hooks.rb

@@ -112,9 +112,9 @@ module Hooks
       #
       # ### Warning: implicit before blocks
       #
-      # `before` hooks can also be declared in shared contexts which get
-      # included implicitly either by you or by extension libraries. Since
-      # RSpec runs these in the order in which they are declared within each
+      # `before` hooks can also be declared in configuration-level shared contexts
+      # which get included implicitly either by you or by extension libraries.
+      # Since RSpec runs these in the order in which they are declared within each
       # scope, load order matters, and can lead to confusing results when one
       # before block depends on state that is prepared in another before block
       # that gets run later.

lib/rspec/core/shared_example_group.rb

@@ -45,9 +45,8 @@ def include_in(klass, inclusion_line, args, customization_block)
     # examples that you wish to use in multiple example groups.
     #
     # When defined, the shared group block is stored for later evaluation.
-    # It can later be included in an example group either explicitly
-    # (using `include_examples`, `include_context` or `it_behaves_like`)
-    # or implicitly (via matching metadata).
+    # It can later be included in an example group explicitly using
+    # `include_examples`, `include_context` or `it_behaves_like`.
     #
     # Named shared example groups are scoped based on where they are
     # defined. Shared groups defined in an example group are available
@@ -62,9 +61,7 @@ module SharedExampleGroup
       # @overload shared_examples(name, metadata, &block)
       #   @param name [String, Symbol, Module] identifer to use when looking up
       #     this shared group
-      #   @param metadata [Array<Symbol>, Hash] metadata to attach to this
-      #     group; any example group or example with matching metadata will
-      #     automatically include this shared example group.
+      #   @param metadata [Array<Symbol>, Hash] metadata to attach to this group
       #   @param block The block to be eval'd
       #
       # Stores the block for later use. The block will be evaluated