Fixed #21722 -- Added a warning for avoiding XSS vulnerabilities when reusing built-in filters.

   handle the auto-escaping issues and return a safe string, the

   ``is_safe`` flag won't change anything either way.

.. warning:: Avoiding XSS vulnerabilities when reusing built-in filters

    Be careful when reusing Django's built-in filters. You'll need to pass

    ``autoescape=True`` to the filter in order to get the proper autoescaping

    behavior and avoid a cross-site script vulnerability.

    For example, if you wanted to write a custom filter called

    ``urlize_and_linebreaks`` that combined the :tfilter:`urlize` and

    :tfilter:`linebreaksbr` filters, the filter would look like::

        from django.template.defaultfilters import linebreaksbr, urlize

        @register.filter

        def urlize_and_linebreaks(text):

            return linebreaksbr(urlize(text, autoescape=True), autoescape=True)

    Then:

    .. code-block:: html+django

        {{ comment|urlize_and_linebreaks }}

    would be equivalent to:

    .. code-block:: html+django

        {{ comment|urlize|linebreaksbr }}

.. _filters-timezones:

Filters and time zones