Minor clarification

"the form" sounded like the HTML form.

| Q             | A
| ------------- | ---
| Doc fix?      | [yes]
| New docs?     | [no]
| Applies to    | [2.3]
| Fixed tickets | []

book/forms.rst

@@ -212,7 +212,7 @@ Handling Form Submissions
 
 The second job of a form is to translate user-submitted data back to the
 properties of an object. To make this happen, the submitted data from the
-user must be written into the form. Add the following functionality to your
+user must be written into ``$form``. Add the following functionality to your
 controller::
 
     // ...