docs, `ActiveRecord::TypeCaster` is not part of the public API.

[ci skip]

activerecord/lib/active_record/type_caster.rb

@@ -2,6 +2,6 @@
 require 'active_record/type_caster/connection'
 
 module ActiveRecord
-  module TypeCaster
+  module TypeCaster # :nodoc:
   end
 end

activerecord/lib/active_record/type_caster/connection.rb

 module ActiveRecord
   module TypeCaster
-    class Connection
+    class Connection # :nodoc:
       def initialize(klass, table_name)
         @klass = klass
         @table_name = table_name

activerecord/lib/active_record/type_caster/map.rb

 module ActiveRecord
   module TypeCaster
-    class Map
+    class Map # :nodoc:
       def initialize(types)
         @types = types
       end