code: public @Nullable Resource getResource(@NotNull Predicate<Resource> filter) {
      return getResource(filter, (Resource)null);
    }
docs: Parse the suffix as resource paths, return the first resource from the suffix (relativ to the current page's
  content) that matches the given filter.
  @param filter a filter that selects only the resource you're interested in.
  @return the resource or null if no such resource was selected by suffix