protected UndoableEdit editToBeUndone() { return null; }
protected UndoableEdit editToBeUndone() { UndoableEdit result;  for (int i = indexOfNextAdd - 1; i >= 0; i--) { result = (UndoableEdit) edits.get(i); if (result.isSignificant()) return result; }  return null; }
	protected UndoableEdit editToBeUndone() {		return null; // TODO	} // editToBeUndone()