Returns the week number of year, for the given <dDate>. Worth to note that the returned value is ISO 8601 compliant.
With this function can also obtained the year and/or the day-number of the week, into <nYear> and <nDayOfWeek> optional parameters, provided they've been passed by reference.
WARNING! 1st day of the week according to ISO 8601 is _Monday_ (and not _Sunday_, as it's widely regarded to be). This may lead to inaccurate/confusing results when the number returned into <nDayOfWeek> is being used as an argument on calling non-ISO 8601-conforming date functions like, for example, hb_CDay(). In such cases, either use _Dow()_ to determine the day number of the week or alternatively _increment by 1_ the <nDayOfWeek> value or pre-increment it with ++ operator, i.e.: hb_CDay( ++nDayOfWeek ).