docs: def _merge_dicts(first, second):
      """Merge the 'second' multiple-dictionary into the 'first' one."""
      new = deepcopy(first)
      for k, v in second.items():
          if isinstance(v, dict) and v:
              ret = _merge_dicts(new.get(k, dict()), v)
              new[k] = ret
          else:
              new[k] = second[k]
      return new