Public Function SubDateTimeSpan(ByVal timespan As dateTimeSpan) As DateTime
  Property Description  
    Method Name SubDateTimeSpan  
    Argument - timespan DateTimeSpan value to subtract  
    Returns The new date time with the time subtracted  
    Description Creates a new DateTime containing this DateTime - DateTimeSpan value  
    Remarks The subtraction is done in compliance with the W3C XML rules for date times and durations (these rules are somewhat convoluted!)