Edge
"edge" is the name given to the current development tree of Alpine Linux. It consists of a APK repository called "edge" and contains the latest build of all available Alpine Linux packages. Those packages are updated on a regular basis.
End users should not use "edge" as their main day-to-day workstation or as productive system. Because "edge" is a development branch, many changes are not heavily tested (or tested at all) and packages in "edge" can and sometimes do break without warning.
However, testing "edge" is a very valuable activity which helps the Alpine Linux development to ensure that the quality of the stable releases is high. Testing "edge" is a great way to contribute to the Alpine Linux development.
An upgrade of Alpine Linux from a stable version to the rolling development version edge basically requires the same steps as Upgrading to latest release.
The crucial difference is, that when editing the /etc/apk/repositories file, all referenced repository versions (such as v3.2 or latest-stable) therein need to be pointing to edge.
When using edge branch, testing repository can be added if the packages that one needs are available only in testing repository.
Contents of /etc/apk/repositories
After upgrading to edge, the currently installed edge version may be checked with
$ cat /etc/alpine-release
and referring to the build date that is attached to the release.