code: public Duration newDurationYearMonth(
              final boolean isPositive,
              final int year,
              final int month) {
          return newDuration(isPositive, year, month,
                  DatatypeConstants.FIELD_UNDEFINED, DatatypeConstants.FIELD_UNDEFINED,
                  DatatypeConstants.FIELD_UNDEFINED, DatatypeConstants.FIELD_UNDEFINED);
      }
docs: <p>Create a <code>Duration</code> of type <code>xdt:yearMonthDuration</code> using the specified
  <code>year</code> and <code>month</code> as defined in
  <a href="http://www.w3.org/TR/xpath-datamodel#dt-yearMonthyDuration">
  XQuery 1.0 and XPath 2.0 Data Model, xdt:yearMonthDuration</a>.</p>
  
  <p>A {@link DatatypeConstants#FIELD_UNDEFINED} value indicates that field is not set.</p>
  
  @param isPositive Set to <code>false</code> to create a negative duration. When the length
  of the duration is zero, this parameter will be ignored.
  @param year Year of <code>Duration</code>.
  @param month Month of <code>Duration</code>.
  
  @return New <code>Duration</code> created using the specified <code>year</code> and <code>month</code>.
  
  @throws IllegalArgumentException If any values would create an invalid <code>Duration</code>.