* ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
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*
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* @typeParam DateType - The `Date` type, the function operates on. Gets inferred from passed arguments. Allows to use extensions like [`UTCDate`](https://github.com/date-fns/utc).
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*
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* @param date - The given date
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*
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* @returns The ISO week
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*
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* @example
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* // Which week of the ISO-week numbering year is 2 January 2005?