- * Function to get the current time window of the current tab.
- *
- * @param tab the tab the viewer belongs to.
- * @return the current tab's time interval.
+ * Function to get the current time interval shown on the current tab.
+ * It will be called by a viewer's hook function to update the
+ * shown time interval of the viewer and also be called by the constructor
+ * of the viewer.
+ * @param tab viewer's tab
+ * @return time window.