public function get_visible_items()
	{
		if ($this->_items === NULL) {
			return array();
		}

		$visible_items = [];

		foreach ($this->_items as $key => $item)
		{
			if (! $item->is_visible())
			{
				continue;
			}
			$visible_items[$key] = $item;
		}

		return $visible_items;
	}