minor #5643 Document how to customize the prototype (daFish, WouterJ)

This PR was merged into the 2.3 branch.

Discussion
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Document how to customize the prototype

Finishes #4629 and #4797

| Q | A
| --- | ---
| Doc fix? | no
| New docs? | yes
| Applies to | all
| Fixed tickets | -

Commits
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ce8110c Improve docs on customizing prototype rendering
051a23f document how to render custom collection prototypes

Author: xabbuh

cookbook/form/form_collections.rst

@@ -262,7 +262,7 @@ great, your user can't actually add any new tags yet.
 .. _cookbook-form-collections-new-prototype:
 
 Allowing "new" Tags with the "Prototype"
------------------------------------------
+----------------------------------------
 
 Allowing the user to dynamically add new tags means that you'll need to
 use some JavaScript. Previously you added two tags to your form in the controller.
@@ -417,6 +417,11 @@ into new ``Tag`` objects and added to the ``tags`` property of the ``Task`` obje
 
     You can find a working example in this `JSFiddle`_.
 
+.. seealso::
+
+    If you want to customize the HTML code in the prototype, read
+    :ref:`cookbook-form-custom-prototype`.
+
 To make handling these new tags easier, add an "adder" and a "remover" method
 for the tags in the ``Task`` class::
 

cookbook/form/form_customization.rst

@@ -734,6 +734,49 @@ You can also override the markup for an entire field row using the same method:
             <?php echo $view['form']->widget($form) ?>
         </div>
 
+.. _cookbook-form-custom-prototype:
+
+How to Customize a Collection Prototype
+---------------------------------------
+
+When using a :doc:`collection of forms </cookbook/form/form_collections>`,
+the prototype can be overridden with a completely custom prototype by
+overriding a block. For example, if your form field is named ``tasks``, you
+will be able to change the widget for each task as follows:
+
+.. configuration-block::
+
+    .. code-block:: html+jinja
+
+        {% form_theme form _self %}
+
+        {% block _tasks_entry_widget %}
+            <tr>
+                <td>{{ form_widget(task.task) }}</td>
+                <td>{{ form_widget(task.dueDate) }}</td>
+            </tr>
+        {% endblock %}
+
+    .. code-block:: html+php
+
+        <!-- src/AppBundle/Resources/views/Form/_tasks_entry_widget.html.php -->
+        <tr>
+            <td><?php echo $view['form']->widget($form->task) ?></td>
+            <td><?php echo $view['form']->widget($form->dueDate) ?></td>
+        </tr>
+
+Not only can you override the rendered widget, but you can also change the
+complete form row or the label as well. For the ``tasks`` field given above,
+the block names would be the following:
+
+================  =======================
+Part of the Form  Block Name
+================  =======================
+``label``         ``_tasks_entry_label``
+``widget``        ``_tasks_entry_widget``
+``row``           ``_tasks_entry_row``
+================  =======================
+
 Other common Customizations
 ---------------------------