future: allow explicit group; cancel: invalidate group identifier for all future members; tuned comments; tuned;
future: allow explicit group;
cancel: invalidate group identifier for all future members;
tuned comments;
tuned;

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle