code: @Override
      public SignatureVisitor visitSuperclass() {
          if (type != CLASS_SIGNATURE || (state & (EMPTY | FORMAL | BOUND)) == 0) {
              throw new IllegalArgumentException();
          }
          state = SUPER;
          SignatureVisitor v = sv == null ? null : sv.visitSuperclass();
          return new CheckSignatureAdapter(TYPE_SIGNATURE, v);
      }
docs: class signatures