[cctbxbb] Backwards compatibility; Python 2.3?

Hi All, I'm starting to go through and learn some of the structure of these packages, starting with libtbx. What's the supported targets supposed to be? There seems to be code specifically marked as backwards compatibility for Python 2.3 (2003), and packages explicitly included that were merged into the standard library around the same time (e.g. Optik). Is this really as far back as we need to support? Thanks, Nick Devenish