docs: @Override
      protected void writeKey(Writer writer, FieldDescriptor key) throws IOException {
          writer.write(key.getClassDescriptor().getDottedClassName());
          writer.write(",");
          writer.write(key.getName());
          writer.write(",");
          writer.write(key.getSignature());
          writer.write(",");
          XField xField = XFactory.createXField(key);
          int flags = xField.getAccessFlags() & 0xf;
          writer.write(String.valueOf(flags));
      }