returns a String representation of _y_ suitable for inclusion in an ISO 8601 string, either in 4-digit format or 6-digit format with sign.</dd>
      </dl>
      <emu-alg>
        1. If _y_ ‚â• 0 and _y_ ‚â§ 9999, then
          1. Return ToZeroPaddedDecimalString(_y_, 4).
        1. If _y_ > 0, let _yearSign_ be *"+"*; otherwise, let _yearSign_ be *"-"*.
        1. Let _year_ be ToZeroPaddedDecimalString(abs(_y_), 6).
        1. Return the string-concatenation of _yearSign_ and _year_.
      </emu