Minor reword

forms.rst

@@ -950,12 +950,11 @@ the submitted data, those fields will be explicitly set to ``null``.
 Extra fields
 ~~~~~~~~~~~~
 
-All form fields are considered properties of the object but you can inject
-fields directly into your view without specifying them in the form definition.
-They can be retrieved via the :method:`FormInterface::getExtraData() <Symfony\\Component\\Form\\FormInterface::getExtraData>`
-method.
+By default, Symfony expects every submitted field to be defined in the form. Any
+additional submitted fields are treated as "extra fields". You can access them via the
+:method:`FormInterface::getExtraData() <Symfony\\Component\\Form\\FormInterface::getExtraData>` method.
 
-This is a creation user form::
+For example, consider a user creation form::
 
     // ...
     use App\User;
@@ -981,7 +980,8 @@ This is a creation user form::
         }
     }
 
-The extra fields can be injected like this:
+You can render an additional input in the template without adding it to the form
+definition:
 
 .. code-block:: html+twig
 
@@ -990,20 +990,22 @@ The extra fields can be injected like this:
         {{ form_row(form.username) }}
         {{ form_row(form.email) }}
 
-        {# Hidden field to send additional referral code #}
+        {# hidden field to send an additional referral code #}
         <input type="hidden" name="{{ form.vars.full_name ~ '[referralCode]' }}" value="{{ referralCode }}"/>
 
         <button type="submit">Submit</button>
     {{ form_end(form) }}
 
-Here, the referral code is an extra field injected at view level.
-
-You can get the referral code via ``getExtraData``::
+In this example, ``referralCode`` is submitted as an extra field and you can
+read it like this::
 
     $extraData = $form->getExtraData();
     $referralCode = $extraData['referralCode'] ?? null;
-    
-> Don't forget to set :ref:`allow_extra_fields <allow-extra-fields>` option to ``true`` on your form
+
+.. note::
+
+    To accept extra fields, set the :ref:`allow_extra_fields <form-option-allow-extra-fields>`
+    option to ``true``. Otherwise, the form will be invalid.
 
 Learn more
 ----------