docs: public static String getNominalValueString(InstancesHeader context,
              int attIndex, int valIndex) {
          if (context != null) {
              int instAttIndex = attIndex < context.classIndex() ? attIndex
                      : attIndex + 1;
              if ((instAttIndex < context.numAttributes())
                      && (valIndex < context.attribute(instAttIndex).numValues())) {
                  return "{val " + (valIndex + 1) + ":"
                          + context.attribute(instAttIndex).value(valIndex) + "}";
              }
          }
          return "{val " + (valIndex + 1) + "}";
      }