ISO 8601-2:2019 standard
Date and time -- Representations for information interchange -- Part 2: Extensions
Introduction
The purpose of this document is to provide a set of date and time format representations for information interchange beyond those supported by [ISO8601-1].
There are various concepts and representations that many applications find useful not supported by [ISO8601-1], including:
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negative values for time scale components;
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qualification of expressions and time scale components;
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set representation of date and time expressions;
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seasons;
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time intervals with open or unknown starts or ends;
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expression of movable days through date and time selection;
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date and time expressions without digit length limits; and
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profiles for specifying feature support amongst ISO 8601 features.
Such concepts are often represented according to various ad-hoc conventions, and this document aims to provide a standard syntax for their representation.
The extended representations allow unambiguous interpretation and enforce the confidence of interoperability and minimize the risk of misinterpretations and their consequences.
Scope
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 [ISO8601-1]. 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:
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uncertain or approximate dates, or dates with portions unspecified;
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extended time intervals;
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divisions of a year;
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sets and choices of calendar dates;
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grouped time scale units;
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repeat rules for recurring time intervals; and
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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 is also not covered.