public function ensure_content_created($region, $output) {
        $this->ensure_instances_exist($region);
        if (!array_key_exists($region, $this->visibleblockcontent)) {
            $contents = array();
            if (array_key_exists($region, $this->extracontent)) {
                $contents = $this->extracontent[$region];
            }
            $contents = array_merge($contents, $this->create_block_contents($this->blockinstances[$region], $output, $region));
            if (($region == $this->defaultregion) && (!isset($this->page->theme->addblockposition) ||
                    $this->page->theme->addblockposition == BLOCK_ADDBLOCK_POSITION_DEFAULT)) {
                $addblockui = block_add_block_ui($this->page, $output);
                if ($addblockui) {
                    $contents[] = $addblockui;
                }
            }
            $this->visibleblockcontent[$region] = $contents;
        }
    }