This document specifies additional representations of dates of the Gregorian calendar and times based on the 24-hour clock that extend the basic rules and composite elements of those defined in ISO 8601-1. These representations are specified as character strings for use in information interchange. It is also applicable for representing times and time shifts based on Coordinated Universal Time (UTC).These extensions include:— uncertain or approximate dates, or dates with portions unspecified;— extended time intervals;— divisions of a year;— sets and choices of calendar dates;— grouped time scale units;— repeat rules for recurring time intervals; and— date and time arithmetic.This document excludes the representation of date elements from non-Gregorian calendars, or times not from the 24-hour clock. This document does not address character encoding of representations specified in this document.