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The week starts with Sunday instead of Monday - in the WEEK use

Development language in the editor is English (and there
the default week starts on Sunday. 

As it is a week it is not ifluenced by the start of the year date

 Add a Formua operator with the following code:

#From help#.DayOfYear == 1 ? XIH.SetDateTime("From help", #From help#.AddDays(7)) && XIH.SetDateTime("Until help", #Until help#.AddDays(7)) : true 

Or for the wekly perspective:

XIH.SetDateTime("Until help", #Until help#.AddDays(((int) #From help#.DayOfWeek) == 6 ? 8 : 1)) &&
XIH.SetDateTime("From help", #From help#.AddDays(((int) #From help#.DayOfWeek) == 6 ? 8 : 1)) &&
XIH.SetString("Start", (#Start#).Replace("As from week","").Replace("Mo","").Replace("Su","")) ?