code: void attach() {
      editors.addAll(editorSource.create(workingCopy.size(), 0));
      final int size = workingCopy.size();
      for (int i = 0; i < size; i++) {
        chain.attach(workingCopy.get(i), editors.get(i));
      }
    }
docs: Must be called after construction. This is a two-phase initialization so that ListEditor can
  assign its list field before any sub-editors might call {@link ListEditor#getList()}