'Return a class for the custom model given by parameters ``model_data``.'

@api.model
def _instanciate(self, model_data):

    class CustomModel(models.Model, ):
        _name = encode(model_data['model'])
        _description = model_data['name']
        _module = False
        _custom = True
        _transient = bool(model_data['transient'])
        __doc__ = model_data['info']
    return CustomModel
