In Debian packaging, a version number looks like:
x is called the epoch. According to the Debian policy:
It is provided to allow mistakes in the version numbers of older versions of a package, and also a package's previous version numbering schemes, to be left behind.
While looking at the Debian packages of Vim, I noticed that they used an epoch number as well. What was surprising is that the epoch number was 2, indicating that it had changed twice. What happened during these changes? Were they a purely Debian change, not related to an upstream one?