item_def["description"] = item_description
    # definitions: dict[DefsRef, dict[str, Any]]
    # but mypy complains about general str in other places that are not declared as
    # DefsRef, although DefsRef is just str:
    # DefsRef = NewType('DefsRef', str)
    # So, a cast to simplify the types here
    return field_mapping, cast(dict[str, dict[str, Any]], definitions)