'The index of the model set axis--that is the axis of a parameter array
that pertains to which model a parameter value pertains to--as
specified when the model was initialized.
See the documentation on `Model Sets
<http://docs.astropy.org/en/stable/modeling/models.html#model-sets>`_
for more details.'

@property
def model_set_axis(self):

    return self._model_set_axis
