code: @SuppressWarnings("unchecked") // we know that the returning fragment is child of fragment.
      @TargetApi(Build.VERSION_CODES.HONEYCOMB)
      public static <F extends android.support.v4.app.Fragment> F supportFindFragmentByTag(android.support.v4.app.FragmentManager manager, String tag) {
          return (F) manager.findFragmentByTag(tag);
      }
docs: Find a fragment that is under {@link android.support.v4.app.FragmentManager}'s control by the tag string.
  @param manager the fragment manager.
  @param tag the fragment tag.
  @param <F> the concrete fragment class parameter.
  @return the fragment.