docs: public Datatype.Builder mutateNestedClasses(Consumer<? super List<Excerpt>> mutator) {
      if (nestedClasses instanceof ImmutableList) {
        nestedClasses = new ArrayList<>(nestedClasses);
      }
      // If addNestedClasses is overridden, this method will be updated to delegate to it
      mutator.accept(nestedClasses);
      return (Datatype.Builder) this;
    }