@Contract(pure = true)
  public static @NotNull Collector<HtmlChunk, ?, HtmlChunk> toFragment(HtmlChunk separator) {
    return Collector.of(HtmlBuilder::new, (hb, c) -> {
      if (!hb.isEmpty()) {
        hb.append(separator);
      }
      hb.append(c);
    }, (hb1, hb2) -> {
      if (!hb1.isEmpty()) {
        hb1.append(separator);
      }
      return hb1.append(hb2);
    }, HtmlBuilder::toFragment);
  }
@Contract(pure = true)
  public static @NotNull Collector<HtmlChunk, ?, HtmlChunk> toFragment(HtmlChunk separator)