code: public static final String printDuration(MSPDIWriter writer, Duration duration)
     {
        String result = null;
  
        if (duration != null && duration.getDuration() != 0)
        {
           result = printDurationMandatory(writer, duration);
        }
  
        return (result);
     }
docs: Print duration.
  
  Note that Microsoft's xsd:duration parser implementation does not
  appear to recognise durations other than those expressed in hours.
  We use the compatibility flag to determine whether the output
  is adjusted for the benefit of Microsoft Project.
  
  @param writer parent MSPDIWriter instance
  @param duration Duration value
  @return xsd:duration value