code: public static StyleSpan bold(int i) {
          if (sBolds == null) {
              sBolds = new ArrayList<>();
              sBolds.add(bold());
          }
          if (i < sBolds.size()) {
              return sBolds.get(i);
          } else {
              StyleSpan bold = new StyleSpan(Typeface.BOLD);
              sBolds.add(bold);
              return bold;
          }
      }
docs: Get a cached bold span.
  
  @param i starts at zero
  @since 2.6.0