docs: def parse_extra_model_fields(extra_model_fields):
      """
      Parses the value of EXTRA_MODEL_FIELDS, grouping the entries by model
      and instantiating the extra fields. Returns a sequence of tuples of
      the form (model_key, fields) where model_key is a pair of app_label,
      model_name and fields is a list of (field_name, field_instance) pairs.
      """
      fields = defaultdict(list)
      for entry in extra_model_fields:
          model_key, field_name = parse_field_path(entry[0])
          field_class = import_field(entry[1])
          field_args, field_kwargs = entry[2:]
          try:
              field = field_class(*field_args, **field_kwargs)
          except TypeError as e:
              raise ImproperlyConfigured(
                  "The EXTRA_MODEL_FIELDS setting contains arguments for the "
                  "field '%s' which could not be applied: %s" % (entry[1], e))
          fields[model_key].append((field_name, field))
      return fields