The nsclean step has the following optional arguments to control
the behavior of the processing.
--mask_spectral_regions(boolean, default=True)- Mask regions in IFU and MOS images that are within the bounding boxes for each slice or slitlet defined in the WCS object of the image.
--n_sigma(float, default=5.0)- The sigma-clipping threshold to use when searching for outliers and illuminated pixels to be excluded from use in the fitting process.
--save_mask(boolean, default=False)- A flag to indicate whether the mask constructed by the step should be saved to a file.
--user_mask(string, default=None)- Path to a user-supplied mask file. If supplied, the mask is used directly and the process of creating a mask in the step is skipped.