The current stable release series is 4.0. The current development release series

is 5.0. Each release series is represented by a branch with the major and minor

version numbers, e.g. 4.0 or 5.0. This branch is updated during the lifecycle of

the release series. Specific releases are represented as tags with the full

version number, e.g. 4.0.0 or 5.0development.0.

If you are making a bug fix to the current stable release, you should

work off of the stable branch, 4.0. If you are adding features or improving

functionality, work off of master. The maintainers will merge master into the

development series branch periodically. We will also occasionally merge ruleset

fixes from master into the stable branch if the ruleset is important (i.e. a

popular or high-security site), or if the version in stable is clearly broken.