docs: def str_to_v2_str(xml_str):
      """Convert a API v1 XML doc to v2 XML doc.
  
      All v1 elements are valid for v2, so only changes namespace.
  
      Args:
        xml_str : str
          API v1 XML doc. E.g.: ``SystemMetadata v1``.
  
      Returns:
        str : API v2 XML doc. E.g.: ``SystemMetadata v2``.
  
      """
      if str_is_v2(xml_str):
          return xml_str
      etree_obj = str_to_etree(xml_str)
      etree_replace_namespace(etree_obj, d1_common.types.dataoneTypes_v2_0.Namespace)
      return etree_to_str(etree_obj)