code: private String parseFormatDescription(final String pattern, final ParsePosition pos) {
          final int start = pos.getIndex();
          seekNonWs(pattern, pos);
          final int text = pos.getIndex();
          int depth = 1;
          for (; pos.getIndex() < pattern.length(); next(pos)) {
              switch (pattern.charAt(pos.getIndex())) {
              case START_FE:
                  depth++;
                  break;
              case END_FE:
                  depth--;
                  if (depth == 0) {
                      return pattern.substring(text, pos.getIndex());
                  }
                  break;
              case QUOTE:
                  getQuotedString(pattern, pos);
                  break;
              default:
                  break;
              }
          }
          throw new IllegalArgumentException(
                  "Unterminated format element at position " + start);
      }
docs: Parse the format component of a format element.
  
  @param pattern string to parse
  @param pos current parse position
  @return Format description String