The amount of intervening time is expressed by a duration as described in the previous section. The two time points start and end are expressed by either a combined date and time representation or just a date representation.
There are four ways to express a time interval: Start and end, such as "T This feature of the standard allows for concise representations of time intervals. For example, the date of a two-hour meeting including the start and finish times could be simply shown as "T If greater precision is desirable to represent the time interval, then more time elements can be added to the representation. To explicitly include all of the start and end dates, the interval would be represented as "T Leaving out the value for [n] means an unbounded number of repetitions.
If the interval specifies the start forms 1 and 2 above , then this is the start of the repeating interval. If the interval specifies the end but not the start form 3 above , then this is the end of the repeating interval. Truncated representations[ edit ] ISO This provision was removed in ISO Usage[ edit ] On the Internet , the World Wide Web Consortium W3C uses ISO in defining a profile of the standard that restricts the supported date and time formats to reduce the chance of error and the complexity of software.
It explicitly excludes durations and dates before the common era. The more complex formats such as week numbers and ordinal days are not permitted. RFC intends " This convention regarding " RFC made no claim that any part of its timestamp format conforms to ISO , and so was free to use this convention without conflict. ISO is referenced by several specifications, but the full range of options of ISO is not always used. For example, the various electronic program guide standards for TV, digital radio, etc.
The ISO week date , as of , appeared in its basic form on major brand commercial packaging in the United States. Its appearance depended on the particular packaging, canning, or bottling plant more than any particular brand.
The format is particularly useful for quality assurance, so that production errors can be readily traced to work weeks, and products can be correctly targeted for recall.