sS renderMultiSetAsLines_byPopularity(MultiSet ms, O... _) {
  optPar int padWidth = 7;
  if (ms == null) ret "-";
  new LS l;
  for (O o : ms.highestFirst())
    l.add(lpad(padWidth, n2(ms.get(o))) + ": " + str(o));
  ret lines(l);
}