Merge branch '3.4' into 4.4

* 3.4:
  Rephrasing the "If you render your whole" note (2nd attempt)
  add empty_data to the form HiddenType

Author: javiereguiluz

form/form_collections.rst

@@ -268,12 +268,6 @@ On the rendered page, the result will look something like this:
     If you want to customize the HTML code in the prototype, see
     :ref:`form-custom-prototype`.
 
-.. note::
-
-    If you render your whole "tags" sub-form at once (e.g. ``form_row(form.tags)``),
-    then the prototype is automatically available on the outer ``div`` as
-    the ``data-prototype`` attribute, similar to what you see above.
-
 .. tip::
 
     The ``form.tags.vars.prototype`` is a form element that looks and feels just
@@ -286,6 +280,12 @@ On the rendered page, the result will look something like this:
 
         {{ form_widget(form.tags.vars.prototype.name)|e }}
 
+.. note::
+
+    If you render your whole "tags" sub-form at once (e.g. ``form_row(form.tags)``),
+    the ``data-prototype`` attribute is automatically added to the containing ``div``,
+    and you need to adjust the following JavaScript accordingly.
+
 The goal of this section will be to use JavaScript to read this attribute
 and dynamically add new tag forms when the user clicks a "Add a tag" link.
 This example uses jQuery and assumes you have it included somewhere on your page.

reference/forms/types/hidden.rst

@@ -15,6 +15,7 @@ The hidden type represents a hidden input field.
 +-------------+----------------------------------------------------------------------+
 | Inherited   | - `attr`_                                                            |
 | options     | - `data`_                                                            |
+|             | - `empty_data`_                                                      |
 |             | - `error_mapping`_                                                   |
 |             | - `mapped`_                                                          |
 |             | - `property_path`_                                                   |
@@ -55,6 +56,8 @@ These options inherit from the :doc:`FormType </reference/forms/types/form>`:
 
 .. include:: /reference/forms/types/options/data.rst.inc
 
+.. include:: /reference/forms/types/options/empty_data.rst.inc
+
 .. include:: /reference/forms/types/options/error_mapping.rst.inc
 
 .. include:: /reference/forms/types/options/mapped.rst.inc