The version numbering format for XFree86 4.0.x releases is
M is the major version number (4),
m is the
minor version number (0),
n is the sub-minor version number,
x is a letter. Full release versions up to and including
4.0.2 were 4.0, 4.0.1, and 4.0.2. Between-release snapshots are
indicated by including
x, a lower case letter. For example,
the first post-4.0.1 snapshot was 4.0.1a. Release candidates have
been indicated by setting
x to a one or two letter combination
with the first letter being "Z". For example, 4.0.1Z was the first
4.0.2 release candidate.
The next 4.0.x release will be an update release, not a full release. These update releases will be indicated by incrementing the sub-minor version number. So, the first post-4.0.2 update release will be 4.0.3. Between-release snapshots will continue to be indicated with a lower case letter, so the first pre-4.0.3 snapshot will be 4.0.2a.
The following example illustrates the release sequence from 4.0 through to the post-4.0.2 update releases.
The 4.0 release.
The first post-4.0 development snapshot.
The sixth post-4.0 development snapshot.
The 4.0.1 release candidate.
The 4.0.1 release.
The first post-4.0.1 development snapshot.
The sixth post-4.0.1 development snapshot.
The first 4.0.2 release candidate.
The third 4.0.2 release candidate.
The 4.0.2 release.
The first pre-4.0.3 snapshot/release candidate.
The third pre-4.0.3 snapshot/release candidate.
The 4.0.3 update release.
The first pre-4.0.4 snapshot/release candidate.
The 4.0.4 update release.