docs: private void showFragment(ShowcaseFragment fragment) {
      final FragmentTransaction fragmentTransaction = getSupportFragmentManager()
          .beginTransaction()
          .replace(R.id.content_main, (Fragment) fragment);
      if (fragment.getBackstackTag() != null) {
        fragmentTransaction.addToBackStack(fragment.getBackstackTag());
      }
      fragmentTransaction.commit();
  
      setTitle(fragment.getTitleId());
    }