This section is included mostly for historical reasons.
The development leading up to 4.0 started from version 3.2A, but much of it happened on a separate development branch. The "new design" work on that development branch was first folded into the main development branch at version 3.9N. Up until the XFree86 CVS was made publicly available, all versions containing one or more letters were internal development snapshots. The internal development snapshots continued through the following sequence: 3.9N, 3.9Na, ..., 3.9Nz, 3.9P, 3.9Pa, ..., 3.9Py, 3.9.15, 3.9.15a, ..., 3.9.16, 3.9.16a, ..., 3.9.17, 3.9.17a, ..., 3.9.18, 3.9.18a, ..., 4.0. The 3.9.15, 3.9.16, etc versions were public pre-4.0 beta releases.