Android: Navigationのdialogタグ周りのコードちょっと読んでみた

/*
 * Copyright 2019 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
...
@Nullable
@Override
public NavDestination navigate(@NonNull final Destination destination, @Nullable Bundle args,
        @Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
    ...

    final Fragment frag = mFragmentManager.getFragmentFactory().instantiate(
            mContext.getClassLoader(), className);
    if (!DialogFragment.class.isAssignableFrom(frag.getClass())) {
        throw new IllegalArgumentException("Dialog destination " + destination.getClassName()
                + " is not an instance of DialogFragment");
    }
    final DialogFragment dialogFragment = (DialogFragment) frag;
    dialogFragment.setArguments(args);
    dialogFragment.getLifecycle().addObserver(mObserver);

    dialogFragment.show(mFragmentManager, DIALOG_TAG + mDialogCount++);

    return destination;
}
...