+ /**
+ * Constants for self::getKey()
+ * @since 1.30
+ */
+
+ /** Use only current data */
+ const USE_CURRENT_ONLY = 0;
+
+ /** Use expired data if current data is unavailable */
+ const USE_EXPIRED = 1;
+
+ /** Use expired data or data from different revisions if current data is unavailable */
+ const USE_OUTDATED = 2;
+
+ /**
+ * Use expired data and data from different revisions, and if all else
+ * fails vary on all variable options
+ */
+ const USE_ANYTHING = 3;
+