private static InvalidOperationException CreateMissingAddMethodException (Type type, string inheritFrom, Type argumentType) {
return new InvalidOperationException (string.Format(CultureInfo.InvariantCulture,
"To be XML serializable, types which inherit from {0} must have " +
"an implementation of Add({1}) at all levels of their inheritance " +
"hierarchy. {2} does not implement Add({1}).", inheritFrom,
argumentType.FullName, type.FullName));
}