I believe that the documentation should be updated. Since the lowest supported version of the java jdk is 1.5, the lowest IBM Websphere server is 6.1, not '5.1 - 6.0'.
I discovered this by trying to add a a4j:keepAlive to an application running on a Websphere 6.0. I was missing the Boolean.parseBoolean method which is only available in jdk 1.5.
