code: def _add_meta_dict_to_xml(self, doc, parent, meta_dict):
          
          if not meta_dict:
              return
          key_list = list(meta_dict.keys())
          key_list.sort()
          for key in key_list:
              el_list = _index_list_of_values(meta_dict, key)
              for el in el_list:
                  self._add_meta_value_to_xml_doc(doc, parent, el)
docs: Values in the meta element dict are converted to a BadgerFish-style
              encoding (see _convert_hbf_meta_val_for_xml), so regardless of input_format,
              we treat them as if they were BadgerFish.