docs: private static String processMsgPartsHelper(
        ImmutableList<SoyMsgPart> parts, Function<String, String> escaper) {
      StringBuilder rawMsgTextSb = new StringBuilder();
      for (SoyMsgPart part : parts) {
        if (part instanceof SoyMsgRawTextPart) {
          rawMsgTextSb.append(escaper.apply(((SoyMsgRawTextPart) part).getRawText()));
        }
  
        if (part instanceof SoyMsgPlaceholderPart) {
          String phName = ((SoyMsgPlaceholderPart) part).getPlaceholderName();
          rawMsgTextSb.append("{" + phName + "}");
        }
      }
      return rawMsgTextSb.toString();
    }