Hi, In the user manual, section "How to Install a Plugin"[1], one can read: 2. Put in this new folder the plugin descriptor file plugin.xml, the Java classes of the plugin and the other files that are referenced in the descriptor file. What does exacty "put the Java classes in the folder" mean? Is it a JAR file? The class object files themselves? In a directory corresponding to the package name? I tried all of those three possibilities, I have the following in <oxygen-12.1>/plugins/ (given the package my classes are in is org.example.test): plugins/my-plugin/plugin.xml plugins/my-plugin/my-plugin.jar plugins/my-plugin/MyPlugin.class plugins/my-plugin/MyExtension.class plugins/my-plugin/org/example/test/MyPlugin.class plugins/my-plugin/org/example/test/MyExtension.class The plugin.xml descriptor is: <!DOCTYPE plugin SYSTEM "../plugin.dtd"> <plugin name="MyPlugin" description="My first plugin" version="0.1.0" vendor="fgeorges.org" class="org.example.test.MyPlugin"> <extension type="selectionProcessor" class="org.example.test.MyExtension"/> </plugin> When I start oXygen 12.1, it says it does not find the extension class. How exctaly should I install the Java classes of the plugin? Regards, -- Florent Georges http://fgeorges.org/ [1]http://www.oxygenxml.com/doc/ug-oxygen/tasks/howto-install-plugin.html