Apache Extras™ for Apache log4j™ is a jar file full of additional functionality for log4j 1.2.x.
Many of these components were originally developed in the discontinued Apache log4j 1.3 development effort.
The package will use the log4j it requires + optional bugfix version after version 1.2. For example, if the Companions release requires log4j 1.2.17 to work, the Companions release will have the version number 1.2.17 too. If new version is necessary, the release will be named 18.104.22.168, 22.214.171.124 and so on.
The component classes implements on log4j 1.2 the component framework from the discontinued log4j 1.3 development activity to support backporting log4j 1.3 code that depends on the framework.