Update serializers.md

 * Add note that any controller reference is acceptable for `serialization_scope`
 * Add note about `ActionController::API` and `view_context` set to `nil`, with respect to accessing helpers in a Serializer
 * refs #2144
 * Update CHANGELOG.md

Author: stratigos

CHANGELOG.md

@@ -12,6 +12,7 @@ Features:
 - [#2189](https://github.com/rails-api/active_model_serializers/pull/2189)
   Update version constraint for jsonapi-renderer to `['>= 0.1.1.beta1', '< 0.3']`
   (@tagliala)
+- [#2215](https://github.com/rails-api/active_model_serializers/pull/2215) Update `serializers.md` documentation to denote alternate use cases for `scope`. (@stratigos)
 
 Fixes:
 

docs/general/serializers.md

@@ -294,6 +294,8 @@ end
 Whether you write the method as above or as `object.comments.where(created_by: scope)`
 is a matter of preference (assuming `scope_name` has been set).
 
+Keep in mind that the scope can be set to any available controller reference. This can be utilized to provide access to any other data scopes or presentation helpers. 
+
 ##### Controller Authorization Context
 
 In the controller, the scope/scope_name options are equal to
@@ -311,7 +313,7 @@ current authorization scope when you call `render :json`.
 called on every request.  This was [also a problem](https://github.com/rails-api/active_model_serializers/pull/1252#issuecomment-159810477)
 in [`0.9`](https://github.com/rails-api/active_model_serializers/tree/0-9-stable#customizing-scope).
 
-We can change the scope from `current_user` to `view_context`.
+We can change the scope from `current_user` to `view_context`, which is included in subclasses of `ActionController::Base`.
 
 ```diff
 class SomeController < ActionController::Base
@@ -379,6 +381,7 @@ class PostsController < ActionController::Base
   end
 end
 ```
+Note that any controller reference which provides the desired scope is acceptable, such as another controller method for loading a different resource or reference to helpers. For example, `ActionController::API` does not include `ActionView::ViewContext`, and would need a different reference for passing any helpers into a serializer via `serialization_scope`. 
 
 #### #read_attribute_for_serialization(key)