%!demo
%! ## As a `calendarDuration` method, `calweeks` returns the day part of the span
%! ## as a whole number of weeks.
%!
%! d = calendarDuration (0, 0, 40)
%! calweeks (d)

%!demo
%! ## Weeks round towards negative infinity, so a negative span rounds away from
%! ## zero: -15 days is -3 weeks, not -2.  As with `caldays`, a span carrying any
%! ## month cannot be stated in weeks at all.
%!
%! calweeks (calendarDuration (0, 0, [-15, -8, -7, -1, 0, 6, 7, 15]))
