# fn:dateTime - XPath XQuery Reference

Returns an xs:dateTime value created by combining an xs:date
            and an xs:time.deterministiccontext-independentfocus-independentIf either $arg1 or $arg2 is the empty sequence the function
            returns the empty sequence.Otherwise, the function returns an xs:dateTime whose date component is
            equal to $arg1 and whose time component is equal to $arg2.The timezone of the result is computed as follows:If neither argument has a timezone, the result has no timezone.If exactly one of the arguments has a timezone, or if both arguments have the same
                  timezone, the result has this timezone.fn:dateTime(xs:date("1999-12-31"),
                  xs:time("12:00:00"))xs:dateTime("1999-12-31T12:00:00")fn:dateTime(xs:date("1999-12-31"),
                  xs:time("24:00:00"))xs:dateTime("1999-12-31T00:00:00")This is because "24:00:00" is an alternate lexical form
                  for "00:00:00"A dynamic error is raised  if the two arguments both
            have timezones and the timezones are different.