Fixed #23114 -- Clarified documentation of template lookups.

    following lookups, in this order:

    * Dictionary lookup

    * Attribute lookup

    * Method call

    * List-index lookup

    * Attribute or method lookup

    * Numeric index lookup

    This can cause some unexpected behavior with objects that override

    dictionary lookup. For example, consider the following code snippet that

    attempts to loop over a ``collections.defaultdict``::

    If the resulting value is callable, it is called with no arguments. The

    result of the call becomes the template value.

    This lookup order can cause some unexpected behavior with objects that

    override dictionary lookup. For example, consider the following code snippet

    that attempts to loop over a ``collections.defaultdict``::

        {% for k, v in defaultdict.iteritems %}

            Do something with k and v here...