Apparently EnforceSummary is no longer compatible with the current version of dokuwiki (hogfather).
I am currently looking for an alternative way to achieve the same thing.
@turnermm helped me in the past by telling me how to disable "minor changes" (which I need but was not covered by the EnforceSummary plugin). I hope this still works in hogfather, though.
Could something like this (a custom css or js file) force users to fill the summary field in hogfather? I guess not, right?
Thanks a lot for your feedback.