code: public int parseInto(ReadWritablePeriod period, String text, int position) {
          checkParser();
          checkPeriod(period);
          
          return getParser().parseInto(period, text, position, iLocale);
      }
docs: Parses a period from the given text, at the given position, saving the
  result into the fields of the given ReadWritablePeriod. If the parse
  succeeds, the return value is the new text position. Note that the parse
  may succeed without fully reading the text.
  <p>
  The parse type of the formatter is not used by this method.
  <p>
  If it fails, the return value is negative, but the period may still be
  modified. To determine the position where the parse failed, apply the
  one's complement operator (~) on the return value.
  
  @param period  a period that will be modified
  @param text  text to parse
  @param position position to start parsing from
  @return new position, if negative, parse failed. Apply complement
  operator (~) to get position of failure
  @throws IllegalArgumentException if any field is out of range