➜  Headers  grep "isValid" *
`NSCalendar.h:- (BOOL)isValidDate NS_AVAILABLE(10_9, __NSCALENDAR_COND_IOS_7_0);`
`NSCalendar.h:- (BOOL)isValidDateInCalendar:(NSCalendar *)calendar NS_AVAILABLE(10_9, `__NSCALENDAR_COND_IOS_7_0);
`NSJSONSerialization.h:+ (BOOL)isValidJSONObject:(id)obj;`
`NSPort.h:- (BOOL)isValid;`