The spec currently says The number of days in the date's week. for [[DaysInWeek]].

What are the situations where this number will not be 7? Is this intended to encompass a wider notion of "week" that can cover things like the multiple "weeks" in the Javanese calendar, or the 10-day cycles in the French republican calendar? If so, we should be specific, since in a calendrical concept by default "week" means the regular 7-day week. The spec also very much assumes that weeks in Durations are just sugar for 7 days.

Perhaps we should standardize this to the number 7.