WP_Rewrite::get_month_permastruct()

	public function get_month_permastruct() {
		$structure = $this->get_date_permastruct();

		if ( empty($structure) )
			return false;

		$structure = str_replace('%day%', '', $structure);
		$structure = preg_replace('#/+#', '/', $structure);

		return $structure;
	}