FA-76915 / Calendar recurrence rules / Member archive

Monthly ordinal BYDAY such as 2TU or -1FR: count basis · case 05

A 5th-weekday series returns fewer than COUNT instances because skipped months are counted.

Member previewVariant 5 · 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	`["2024-03-29", "2024-05-31"]`	`["2024-03-29", "2024-05-31", "2024-08-30", "2024-11-29"]`	Failed

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