FA-76908 / Calendar recurrence rules / Member archive

Monthly ordinal BYDAY such as 2TU or -1FR: missing occurrence · case 03

A 5th-Monday series reports the 4th Monday in months without a fifth one.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

FREQ=MONTHLY;BYDAY=<ordinal><weekday>. weekday is 0=Monday..6=Sunday; ordinal 1..5 counts from the start of the month and -1..-5 from the end. A month lacking that occurrence is skipped and does not consume COUNT. Months step by interval from the dtstart month; instances before dtstart are dropped. Return the first count ISO dates.

Why this case matters

Recurring calendar series are expanded into concrete instances for display, reminders and conflict checks.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
fifth friday interval 1	`["2024-02-23", "2024-03-29", "2024-04-26", "2024-05-31"]`	`["2024-03-29", "2024-05-31", "2024-08-30", "2024-11-29"]`	Failed

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