docs: def flatten_model(model):
      """Flatten a model to a list of models.
      This is used to flatten a ``Binder``'ish model down to a list
      of contained models.
      """
      yield model
      if isinstance(model, (TranslucentBinder, Binder,)):
          for m in model:
              # yield from flatten_model(m)
              for x in flatten_model(m):
                  yield x