feature #3875 Added a note about customizing a form with more than one template (javiereguiluz)

This PR was merged into the 2.3 branch.

Discussion
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Added a note about customizing a form with more than one template

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #3643

Commits
-------

ce14104 Fixed a minor grammar mistake
1b386ff Fixed a minor error
08d26ee Removed the old syntax and left just the "with" keyword syntax
94625c5 Fixed minor formatting issue
6621720 Minor formatting improvement
2b0213b Added a note about customizing a form with more than one template

Author: weaverryan

cookbook/form/form_customization.rst

@@ -298,6 +298,22 @@ When the ``form.age`` widget is rendered, Symfony will use the ``integer_widget`
 block from the new template and the ``input`` tag will be wrapped in the
 ``div`` element specified in the customized block.
 
+Multiple Templates
+..................
+
+A form can also be customized by applying several templates. To do this, pass the
+name of all the templates as an array using the ``with`` keyword:
+
+.. code-block:: html+jinja
+
+    {% form_theme form with ['::common.html.twig', ':Form:fields.html.twig',
+                             'AcmeDemoBundle:Form:fields.html.twig'] %}
+
+    {# ... #}
+
+The templates can be located at different bundles and they can even be stored
+at the global ``app/Resources/views/`` directory.
+
 Child Forms
 ...........