It takes 4 spaces or some backticks to have this code displayed as code in the changelog.

activerecord/CHANGELOG.md

@@ -11,33 +11,33 @@
 *   Ambiguous reflections are on :through relationships are no longer supported.
     For example, you need to change this:
 
-      class Author < ActiveRecord::Base
-        has_many :posts
-        has_many :taggings, :through => :posts
-      end
+        class Author < ActiveRecord::Base
+          has_many :posts
+          has_many :taggings, :through => :posts
+        end
 
-      class Post < ActiveRecord::Base
-        has_one :tagging
-        has_many :taggings
-      end
+        class Post < ActiveRecord::Base
+          has_one :tagging
+          has_many :taggings
+        end
 
-      class Tagging < ActiveRecord::Base
-      end
+        class Tagging < ActiveRecord::Base
+        end
 
     To this:
 
-      class Author < ActiveRecord::Base
-        has_many :posts
-        has_many :taggings, :through => :posts, :source => :tagging
-      end
+        class Author < ActiveRecord::Base
+          has_many :posts
+          has_many :taggings, :through => :posts, :source => :tagging
+        end
 
-      class Post < ActiveRecord::Base
-        has_one :tagging
-        has_many :taggings
-      end
+        class Post < ActiveRecord::Base
+          has_one :tagging
+          has_many :taggings
+        end
 
-      class Tagging < ActiveRecord::Base
-      end
+        class Tagging < ActiveRecord::Base
+        end
 
 *   Remove column restrictions for `count`, let the database raise if the SQL is
     invalid. The previous behavior was untested and surprising for the user.
@@ -70,9 +70,9 @@
     You can turn off the automatic detection of inverse associations by setting
     the `:inverse_of` option to `false` like so:
 
-      class Taggable < ActiveRecord::Base
-        belongs_to :tag, inverse_of: false
-      end
+        class Taggable < ActiveRecord::Base
+          belongs_to :tag, inverse_of: false
+        end
 
     *John Wang*