code: def security_iter(nodearr):
          
          assert nodearr.Name == 'securityData' and nodearr.IsArray
          for i in range(nodearr.NumValues):
              node = nodearr.GetValue(i)
              err = XmlHelper.get_security_error(node)
              result = (None, err) if err else (node, None)
              yield result
docs: provide a security data iterator by returning a tuple of (Element, SecurityError) which are mutually exclusive