Calculate week in year {dw} according to ISO8601

Currently the week number is not calculated according to ISO8601 which is commonly used in Europe and Australia. The week number calculation seems to follow some rules commonly used in the USA.
It would be great to have a new date property like {dw8601} that will return the correct number of week.
For further reference see:

https://en.wikipedia.org/wiki/ISO_8601
or
https://en.wikipedia.org/wiki/Week#Week_numbering

As only limited lua support is provided, it is nearly impossible to calculate the correct week number with the possibilities given.