added traits support for the parent function

doc/templates.rst

@@ -1628,22 +1628,26 @@ is ignored. To avoid name conflicts, you can rename imported blocks:
     {% block title %}{% endblock %}
     {% block content %}{% endblock %}
 
-Renaming also allows you to simulate inheritance by calling the "parent" block
-(like what you would have done with ``parent()``):
+The ``parent()`` function automatically determines the correct inheritance
+tree, so it can be used when overriding a block defined in an imported
+template:
 
 .. code-block:: jinja
 
     {% extends "base.html" %}
 
-    {% use "blocks.html" with sidebar as parent_sidebar %}
+    {% use "blocks.html" %}
 
     {% block sidebar %}
-        {{ block('parent_sidebar') }}
+        {{ parent() }}
     {% endblock %}
 
     {% block title %}{% endblock %}
     {% block content %}{% endblock %}
 
+In this example, ``parent()`` will correctly call the ``sidebar`` block from
+the ``blocks.html`` template.
+
 .. note::
 
     You can use as many ``use`` statements as you want in any given template.