public function add_fake_block($bc, $region) {
        $this->page->initialise_theme_and_output();
        if (!$this->is_known_region($region)) {
            $region = $this->get_default_region();
        }
        if (array_key_exists($region, $this->visibleblockcontent)) {
            throw new coding_exception('block_manager has already prepared the blocks in region ' .
                    $region . 'for output. It is too late to add a fake block.');
        }
        if (!isset($bc->attributes['data-block'])) {
            $bc->attributes['data-block'] = '_fake';
        }
        $bc->attributes['class'] .= ' block_fake';
        $this->extracontent[$region][] = $bc;
    }