Hi - I know this is an old post, but we're trying to extend the Experience Fragment and I was hoping you could provide a little detail on how you did it to help me out.
We have copied the files under cq/experience-fragments/editor/components/experiencefragment and setting that as the sling:ResourceSuperType. That seems to mostly work, but after doing that, we're unable to drag components onto pages anymore. We can only double-click the "Drag components here" placeholders to add components.