code: function getYearFromAbbreviation(str, d, prefer) {
    // Following IETF here, adding 1900 or 2000 depending on the last two digits.
    // Note that this makes no accordance for what should happen after 2050, but
    // intentionally ignoring this for now. https://www.ietf.org/rfc/rfc2822.txt
    var val = +str, delta;
    val += val < 50 ? 2000 : 1900;
    if (prefer) {
      delta = val - getYear(d);
      if (delta / abs(delta) !== prefer) {
        val += prefer * 100;
      }
    }
    return val;
  }
docs: Parsing helpers