ember.js - Ember {embedded: 'always' } on model Vs Serializer -

i reading through ember docs , examples on working embedded object json in ember.

i came across embeddedrecordsmixin feature , saw can write code below tell embedded record.

import ds 'ember-data';  export default ds.restserializer.extend(ds.embeddedrecordsmixin, {   attrs: {     author: { embedded: 'always' },   } }); 

qouting below ember page

note use of { embedded: 'always' } unrelated { embedded: 'always' } defined option on ds.attr part of defining model while working activemodelserializer. nevertheless, using { embedded: 'always' } option ds.attr not valid way setup embedded records.

and have seen model written this.

app.child = ds.model.extend({   name: ds.attr('string'),   toys: ds.hasmany('toy', {embedded: 'always'}), }); 

where child object has toys object embedded.

going first example, can write child serailizer below?

app.childserializer = ds.restserializer.extend(ds.embeddedrecordsmixin, {   attrs: {     toys: {embedded: 'always'}   } }); 

can me understand difference between these 2 {embedded: 'always'} , use when?

thanks