code: public DateTimeFormatterBuilder appendTwoDigitWeekyear(int pivot, boolean lenientParse) {
          return append0(new TwoDigitYear(DateTimeFieldType.weekyear(), pivot, lenientParse));
      }
docs: Instructs the printer to emit a numeric weekyear field which always prints
  two digits. A pivot year is used during parsing to determine the range
  of supported years as <code>(pivot - 50) .. (pivot + 49)</code>. If
  parse is instructed to be lenient and the digit count is not two, it is
  treated as an absolute weekyear. With lenient parsing, specifying a positive
  or negative sign before the weekyear also makes it absolute.
  
  @param pivot  pivot weekyear to use when parsing
  @param lenientParse  when true, if digit count is not two, it is treated
  as an absolute weekyear
  @return this DateTimeFormatterBuilder, for chaining
  @since 1.1