code: public String getFormatString(CellValueRecordInterface cell) {
          int formatIndex = getFormatIndex(cell);
          if (formatIndex == -1) {
              // Not found
              return null;
          }
          return getFormatString(formatIndex);
      }
docs: Returns the format string, eg $##.##, used by your cell
  
  @param cell the cell
  @return the format string