Apache Geronimo documentation is a community effort, just like with the code. Users and developers alike contribute with content for the documentation. How and where? we discuss that on the mailing lists, check How to contribute to the project's documentation for more details.
To help minimize the overlapping when developing content we are providing tables representing the list of topics matching Geronimo releases. In these tables you can identify yourself as the contributor actively working on any given topic.
So, for Apache Geronimo v2.1 documentation we are updating some of the content from the previous releases as well as adding a whole new set with the recently added features and functions.