def control_group(self, control_group_id, ctrl, shift, alt):
    """Act on a control group, selecting, setting, etc."""
    action = sc_pb.Action()
    select = action.action_ui.control_group

    mod = sc_ui.ActionControlGroup
    if not ctrl and not shift and not alt:
      select.action = mod.Recall
    elif ctrl and not shift and not alt:
      select.action = mod.Set
    elif not ctrl and shift and not alt:
      select.action = mod.Append
    elif not ctrl and not shift and alt:
      select.action = mod.SetAndSteal
    elif not ctrl and shift and alt:
      select.action = mod.AppendAndSteal
    else:
      return  # unknown
    select.control_group_index = control_group_id
    return action