@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
    public Set<RequestManagerFragment> getDescendantRequestManagerFragments() {
        if (rootRequestManagerFragment == this) {
            return Collections.unmodifiableSet(childRequestManagerFragments);
        } else if (rootRequestManagerFragment == null || Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
            // Pre JB MR1 doesn't allow us to get the parent fragment so we can't introspect hierarchy, so just
            // return an empty set.
            return Collections.emptySet();
        } else {
            HashSet<RequestManagerFragment> descendants = new HashSet<RequestManagerFragment>();
            for (RequestManagerFragment fragment
                    : rootRequestManagerFragment.getDescendantRequestManagerFragments()) {
                if (isDescendant(fragment.getParentFragment())) {
                    descendants.add(fragment);
                }
            }
            return Collections.unmodifiableSet(descendants);
        }
    }
Returns the set of fragments that this RequestManagerFragment's parent is a parent to. (i.e. our parent is
the fragment that we are annotating).
core/src/main/java/com/bumptech/glide/manager/RequestManagerFragment.java