Since that is the defined entry point in the above ``setup.py``, flake8 finds
it and uses it to register the extension.
+This is not at all a comprehensive listing of existing extensions but simply a
+listing of the ones we are aware of:
+* `flake8-immediate <https://github.com/schlamar/flake8-immediate>`_
+* `flake8-todo <https://github.com/schlamar/flake8-todo>`_
+* `pep8-naming <https://github.com/flintwork/pep8-naming>`_
.. _mccabe: https://github.com/flintwork/mccabe