docs: def kill_child_processes() -> None:
      """
      Kills children of this process that were registered in the
      :data:`processes` variable.
  
      Use with ``@atexit.register``.
      """
      timeout_sec = 5
      for p in processes:
          try:
              p.wait(timeout_sec)
          except TimeoutExpired:
              # failed to close
              p.kill()