docs: public ZMsg dump(Appendable out)
      {
          try {
              StringWriter sw = new StringWriter();
              PrintWriter pw = new PrintWriter(sw);
              pw.printf("--------------------------------------\n");
              for (ZFrame frame : frames) {
                  pw.printf("[%03d] %s\n", frame.size(), frame.toString());
              }
              out.append(sw.getBuffer());
              sw.close();
          }
          catch (IOException e) {
              throw new RuntimeException("Message dump exception " + super.toString(), e);
          }
          return this;
      }