* Use syntax compatible to both python 2.6+ and 3.1+.
* Use docstrings with pydoc in mind
* Follow the style guide for python code:
    http://www.python.org/dev/peps/pep-0008/
* Test the code with "doctest" where it makes sense
* when breaking backward compatibility with old configuration files or plugins,
  please include a temporary workaround code that provides a compatibility
  layer and mark it with a comment that includes the word "COMPAT".  For
  examples, grep the code for the word "COMPAT". :)