<listitem>

<para>

The number of the week of the year that the day is in. By definition

(<acronym>ISO</acronym> 8601), the first week of a year

contains January 4 of that year. (The <acronym>ISO</acronym>-8601

week starts on Monday.) In other words, the first Thursday of

a year is in week 1 of that year.

(<acronym>ISO</acronym> 8601), weeks start on Mondays and the first

week of a year contains January 4 of that year. In other words, the

first Thursday of a year is in week 1 of that year.

</para>

<para>

Because of this, it is possible for early January dates to be part of the

52nd or 53rd week of the previous year. For example, <literal>2005-01-01</>

is part of the 53rd week of year 2004, and <literal>2006-01-01</> is part of

the 52nd week of year 2005.

In the ISO definition, it is possible for early-January dates to be

part of the 52nd or 53rd week of the previous year, and for

late-December dates to be part of the first week of the next year.

For example, <literal>2005-01-01</> is part of the 53rd week of year

2004, and <literal>2006-01-01</> is part of the 52nd week of year

2005, while <literal>2012-12-31</> is part of the first week of 2013.

It's recommended to use the <literal>isoyear</> field together with

<literal>week</> to get consistent results.

</para>

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