[book] [form] Ambiguous block prefixes render incorrectly

Author: jonny-no1

book/forms.rst

@@ -241,7 +241,7 @@ your controller::
             'form' => $form->createView(),
         ));
     }
-    
+
 .. caution::
 
     Be aware that the ``createView()`` method should be called *after* ``handleRequest``
@@ -686,7 +686,7 @@ the documentation for each type.
     is left blank. If you don't want this behavior, either
     :ref:`disable HTML5 validation <book-forms-html5-validation-disable>`
     or set the ``required`` option on your field to ``false``::
-    
+
         ->add('dueDate', 'date', array(
             'widget' => 'single_text',
             'required' => false
@@ -1128,6 +1128,23 @@ the choice is ultimately up to you.
             ));
         }
 
+.. caution::
+
+    When the name of your form class matches any of the built-in field types,
+    your form might not be rendered correctly. A form
+    ``AppBundle\\Form\\Type\\PasswordType`` to change a user password for
+    instance will be mistaken for the built-in ``PasswordType`` field type and
+    won't be rendered correctly. You can still use the class name of your choice
+    by overriding the ``getBlockPrefix`` method of your form class::
+
+        public function getBlockPrefix()
+        {
+            return 'app_bundle_password';
+        }
+
+    Read the chapter ":doc:`/cookbook/form/create_custom_field_type.html`" for
+    more information.
+
 .. tip::
 
     When mapping forms to objects, all fields are mapped. Any fields on the