Document Twig test "rootform"

Author: yceruto

reference/forms/twig_reference.rst

@@ -217,6 +217,30 @@ array).
 
     <option {% if choice is selectedchoice(value) %} selected="selected"{% endif %} ...>
 
+.. _form-twig-rootform:
+
+rootform
+~~~~~~~~
+
+This test will check for sure if the current ``form`` does not have a parent form view.
+It would avoid collision and odd behavior when your form has defined a ``parent`` field.
+
+Wrong example if your form has a field named ``parent``:
+
+.. code-block:: jinja
+
+    {% if form.parent is null %}
+        {{ form_errors(form) }}
+    {% endif %}
+
+Correct example, this will check for the parent form view rather than its ``parent`` field:
+
+.. code-block:: jinja
+
+    {% if form is rootform %}
+        {{ form_errors(form) }}
+    {% endif %}
+
 .. _`twig-reference-form-variables`:
 
 More about Form Variables

reference/twig_reference.rst

@@ -750,6 +750,19 @@ selectedchoice
 Checks if ``selectedValue`` was checked for the provided choice field. Using
 this test is the most effective way.
 
+rootform
+~~~~~~~~
+
+.. code-block:: twig
+
+    {% if form is rootform %}
+
+``form``
+    **type**: ``FormView``
+
+Checks for sure if the current ``form`` does not have a parent form view. Using
+this test is the safest way if your form contains a ``parent`` field.
+
 Global Variables
 ----------------