th a message indicating implementation limits
 if implementation capacities are exceeded.</p>
 
 <p>A <code>null</code> value indicates that field isnot set.</p>
<P>
<DD><DL>
<DT><B>Parameters:</B><DD><CODE>isPositive</CODE> - Set to <code>false</code> to create a negative duration. When the length
   of the duration is zero, this parameter will be ignored.<DD><CODE>year</CODE> - Year of <code>Duration</code>.<DD><CODE>month</CODE> - Month of <code>Duration</code>.
<DT><B>Returns:</B><DD>New <code>Durati