The flat_field step has one step-specific argument, and it is only relevant for NIRSpec data.
flat_suffix is a string, the suffix to use when constructing the
name of on optional output file for on-the-fly flat fields. If
flat_suffix is specified (and if the input data are NIRSpec),
the extracted and interpolated flat fields will be saved to a file with
this suffix. The default (if
flat_suffix was not specified) is to
not write this optional output file.