def security_iter(nodearr):
        """ provide a security data iterator by returning a tuple of (Element, SecurityError) which are mutually exclusive """
        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
provide a security data iterator by returning a tuple of (Element, SecurityError) which are mutually exclusive