//from compareElementValues:
        case Timestamp:
            // unsigned compare for timestamps - note they are not really dates but (ordinal + time_t)
            if ( l.date() < r.date() )
                return -1;
            return l.date() == r.date() ? 0 : 1;
        case Date:
            {
                long long a = (long long) l.Date().millis;
                long long b = (long long) r.Date().millis;
                if( a < b ) 
                    return -1;
                return a == b ? 0 : 1;
            }