# cannot create new fields for a step

    Code
      update(stp, y = 5)
    Condition
      Error in `update_fields()`:
      ! The step you are trying to update, 'step_stp', does not have the 'y' field.

# cannot update trained steps

    Code
      update(stp, x = 5)
    Condition
      Error in `validate_not_trained()`:
      ! To update 'step_stp', it must not be trained.