GitLab

(calendar-cursor-to-date): Add optional parameter to cause error
signal when cursor is not on a date---this allows lots of
simplifications throughout the code.
(calendar-forward-month,calendar-set-mark,
calendar-exchange-point-and-mark,calendar-count-days-region,
calendar-print-day-of-year,calendar-print-iso-date,
calendar-print-julian-date,calendar-print-islamic-date,
calendar-print-hebrew-date,calendar-print-astro-day-number): Use simplification.