Why does Rails not document the ability to use accepts_nested_attributes_for on children -

from rails documentation: "nested attributes allow save attributes on associated records through parent."

i able save attributes on associated records through child. (which great... why not documented or explained?)

(this project can cloned github at: https://github.com/blasto333/vehicles-demo/)

vehicle model (parent)

class vehicle < activerecord::base   has_one :car   attr_accessible :name, :color, :price, :condition end  # == schema information # # table name: vehicles # #  id         :integer         not null, primary key #  name       :string(255) #  color      :string(255) #  price      :string(255) #  condition  :string(255) #  created_at :datetime #  updated_at :datetime # 

car model (child)

class car < activerecord::base   belongs_to :vehicle   accepts_nested_attributes_for :vehicle   attr_accessible :doors, :sport, :vehicle_attributes end   # == schema information # # table name: cars # #  id         :integer         not null, primary key #  vehicle_id :integer #  doors      :integer #  sport      :boolean #  created_at :datetime #  updated_at :datetime # 

cars controller

class carscontroller < applicationcontroller   def new     @car = car.new     @car.build_vehicle   end    def create     car.create(params[:car])   end  end 

cars "new" view

<h1>cars#new</h1> <%= form_for @car |car_form| %>     <%= car_form.fields_for :vehicle |vehicle_fields| %>         <%=vehicle_fields.label :name%>: <%=vehicle_fields.text_field :name%><br />         <%=vehicle_fields.label :color%>: <%=vehicle_fields.text_field :color%><br />         <%=vehicle_fields.label :price%>: <%=vehicle_fields.text_field :price%><br />         <%=vehicle_fields.label :condition%>: <%=vehicle_fields.text_field :condition%><br />     <% end %>     <%=car_form.label :doors%>: <%=car_form.text_field :doors%><br />     <%=car_form.label :sport%>: <%=car_form.text_field :sport%><br />     <%=car_form.submit%> <% end %> 

http://apidock.com/rails/activerecord/nestedattributes/classmethods/accepts_nested_attributes_for

defines attributes writer specified association(s).  

it means associations: has_many, has_one, belongs_to, habtm. so... looks pretty documented.