-.. _GNU-format: http://www.gnu.org/prep/standards/html_node
- /Style-of-Change-Logs.html#Style-of-Change-Logs
+.. _sdist: https://packaging.python.org/glossary
+ /#term-source-distribution-or-sdist
+
+developer environment
+---------------------
+
+Basic developer requirements are a POSIX Unix derivative (such as
+Linux), a modern Python 3 interpreter (any of the minor revisions
+mentioned in the ``metadata.classifier`` section of setup.cfg_) and
+a recent release of the tox_ utility (at least the
+``tox.minversion`` mentioned in tox.ini_).
+
+.. _setup.cfg: http://mudpy.org/gitweb?p=mudpy.git;a=blob;f=setup.cfg
+.. _tox.ini: http://mudpy.org/gitweb?p=mudpy.git;a=blob;f=tox.ini