# op:add-yearMonthDurations - XPath XQuery Reference

Returns the result of adding two xs:yearMonthDuration values. Defines the semantics of the
         "+" operator when applied to two xs:yearMonthDuration values.The function returns the result of adding the value of $arg1 to the value
            of $arg2. The result will be an xs:yearMonthDuration whose
            length in months is equal to the length in months of $arg1 plus the length
            in months of $arg2.For handling of overflow, see .op:add-yearMonthDurations(xs:yearMonthDuration("P2Y11M"),
                  xs:yearMonthDuration("P3Y3M"))xs:yearMonthDuration("P6Y2M")Either duration (and therefore the result) may be negative.