bug#45608: 28.0.50; calendar-iso-date-string: "Day 6 of week 53 of 2020"

[Drew Adams <drew.adams@oracle.com>]

> > (calendar-iso-date-string) gives following information on this day:
> > "Day 6 of week 53 of 2020" which I consider wrong as it is 2021 and
> > the year has 52 weeks normally, the days at begin of the new year
> > should not be considered past year.
> 
> https://urldefense.com/v3/__https://en.wikipedia.org/wiki/ISO_week_date__;!!G
> qivPVa7Brio!LxlLxRzS6V8fuHzPVAnAczqQvPR708E_qdx6x3He2wfh95sRUnSwi7xVfdtCWDxz$
> 
> "An ISO week-numbering year (also called ISO year informally) has 52 or
> 53 full weeks. That is 364 or 371 days instead of the usual 365 or 366
> days. The extra week is sometimes referred to as a leap week, although
> ISO 8601 does not use this term. Weeks start with Monday. Each week's
> year is the Gregorian year in which the Thursday falls. The first week
> of the year, hence, always contains 4 January. ISO week year numbering
> therefore slightly deviates from the Gregorian for some days close to 1
> January."

Very cool.  Interesting.  Thanks for citing that, Lars.