I seem to remember that in the old days (I am talking Commodore here) we used a syntax like
release.version.revision
which could be appended with either fix and/or build, where fix would usually be a letter stuck directly to the revision. So a full number would read something like:
2.1.44a.786
But like most have already said, it doesn't really matter, there is no true standard for this. Just use whatever is most convenient for you.
