You are looking at documentation for an older release. Not what you want? See the current release documentation.
In order to accommodate the different target runtime where it can be deployed, eXo is capable of leveraging several logging systems. eXo lets you choose the underlying logging engine to use and even configure that engine (as a quick alternative to doing it directly in your runtime environment).
The currently supported logging engines are:
Apache Commons Logging (which is itself a pluggable logging abstraction)