code: public XMLGregorianCalendar addYears(final XMLGregorianCalendar cal, final int amount) {
          XMLGregorianCalendar to = buildXMLGregorianCalendarDate(cal);
          // Add amount of months
          to.add(addYears(amount));
          return to;
      }
docs: Add Years to a Gregorian Calendar.
  
  @param cal The XMLGregorianCalendar source
  @param amount The amount of years. Can be a negative Integer to
  substract.
  @return A XMLGregorianCalendar with the new Date