+- (void)setTransparency:(NSString *)_transparency;
+- (NSString *)transparency;
+
+/* convenience */
+
+- (BOOL)isOpaque;
+- (BOOL)isAllDay;
+
+- (BOOL)isWithinCalendarDateRange:(NGCalendarDateRange *)_range;
+- (NSArray *)recurrenceRangesWithinCalendarDateRange:(NGCalendarDateRange *)_r;
+
+- (NSCalendarDate *)lastPossibleRecurrenceStartDate;
+
+/* calculating changes */
+