Merge pull request rails#13214 from JuanitoFatas/master

Some improvements on building nested forms. [ci skip]

guides/source/form_helpers.md

@@ -859,7 +859,7 @@ end
 
 This creates an `addresses_attributes=` method on `Person` that allows you to create, update and (optionally) destroy addresses.
 
-### Building the Form
+### Nested Forms
 
 The following form allows a user to create a `Person` and its associated addresses.
 
@@ -882,16 +882,18 @@ The following form allows a user to create a `Person` and its associated address
 ```
 
 
-When an association accepts nested attributes `fields_for` renders its block once for every element of the association. In particular, if a person has no addresses it renders nothing. A common pattern is for the controller to build one or more empty children so that at least one set of fields is shown to the user. The example below would result in 3 sets of address fields being rendered on the new person form.
+When an association accepts nested attributes `fields_for` renders its block once for every element of the association. In particular, if a person has no addresses it renders nothing. A common pattern is for the controller to build one or more empty children so that at least one set of fields is shown to the user. The example below would result in 2 sets of address fields being rendered on the new person form.
 
 ```ruby
 def new
   @person = Person.new
-  3.times { @person.addresses.build}
+  2.times { @person.addresses.build}
 end
 ```
 
-`fields_for` yields a form builder that names parameters in the format expected the accessor generated by `accepts_nested_attributes_for`. For example when creating a user with 2 addresses, the submitted parameters would look like
+The `fields_for` yields a form builder. The parameters' name will be what
+`accepts_nested_attributes_for` expects. For example when creating a user with
+2 addresses, the submitted parameters would look like:
 
 ```ruby
 {
@@ -913,7 +915,7 @@ end
 
 The keys of the `:addresses_attributes` hash are unimportant, they need merely be different for each address.
 
-If the associated object is already saved, `fields_for` autogenerates a hidden input with the `id` of the saved record. You can disable this by passing `include_id: false` to `fields_for`. You may wish to do this if the autogenerated input is placed in a location where an input tag is not valid HTML or when using an ORM where children do not have an id.
+If the associated object is already saved, `fields_for` autogenerates a hidden input with the `id` of the saved record. You can disable this by passing `include_id: false` to `fields_for`. You may wish to do this if the autogenerated input is placed in a location where an input tag is not valid HTML or when using an ORM where children do not have an `id`.
 
 ### The Controller
 
@@ -944,15 +946,17 @@ class Person < ActiveRecord::Base
 end
 ```
 
-If the hash of attributes for an object contains the key `_destroy` with a value of '1' or 'true' then the object will be destroyed. This form allows users to remove addresses:
+If the hash of attributes for an object contains the key `_destroy` with a value
+of `1` or `true` then the object will be destroyed. This form allows users to
+remove addresses:
 
 ```erb
 <%= form_for @person do |f| %>
   Addresses:
   <ul>
     <%= f.fields_for :addresses do |addresses_form| %>
       <li>
-        <%= check_box :_destroy%>
+        <%= addresses_form.check_box :_destroy%>
         <%= addresses_form.label :kind %>
         <%= addresses_form.text_field :kind %>
         ...