Thanks for your work on this, Lora! Just updated our dev instance to 2.3.1 and it's working great.

In working through this I realized there was nothing built in to handle the possibility of a single subject encompassing multiple subject terms and term types (e.g. "African Americans – Education, Higher – Maryland" or something of that sort). I have added in logic that joins the subject terms together with " – " as is done elsewhere in the applications, and have selected the first subject term type as the basis for the mods tag. This may be open to further discussion, but at least, for now, the exporter is able to handle instances in which subjects include multiple subdivisions with several terms and term types.

Will need to update export_mods_spec

I think I've got this addressed in a local branch: https://github.com/lorawoodford/archivesspace/tree/ANW-289_mods_exporter_subject_fields

I used the same logic as is present in the MARC21 model to map the ArchivesSpace subject term types to MODS subject types, but could use eyes that know MODS better than I.

I think this should be part of the handle_subjects method in the MODS exporter model: https://github.com/archivesspace/archivesspace/blob/master/backend/app/exporters/models/mods.rb#L173-L180

Here's the corresponding method in the MARC21 model: https://github.com/archivesspace/archivesspace/blob/master/backend/app/exporters/models/marc21.rb#L203-L244