This entire extension module functionality is related to the Java Extension Mechanism. JAR files placed at WFLY_HOME/standalone/lib/ext will be identified as available Java Extensions that your deployment (using entries in the manifest) can declare as needed.

We should improve the javadoc on related classes (maybe ExtensionInfo, ExtensionIndex, any relevant constant in Attachments), since it is a recurrent task to review what those classes do, and also, it is easily confused with a funtionality provided for the WildFly Extensions instead of Java Extension Mechanism.