Gotchas

isnow is compact, and compactness invites a confident wrong reading. These are the ones worth knowing before they bite. When in doubt about what a pattern means, run isnow canon <isnow> to see its fully-qualified canonical form.

The week starts Sunday

Weekday and interval numbering start at Sunday = 1, not Monday. So the interval +[3d] holds on Sunday, Wednesday, Saturday — not Mon/Thu/Sun. If you think in ISO weeks, adjust by one.

Intervals re-align; they don’t free-run

+[25h] is not a clean 25-hour clock ticking forever. It anchors to the week and re-aligns every Sunday, so one gap per week is shorter than 25 hours. Intervals stay glued to the civil calendar by design — that is what keeps +[2h] at local midnight, 02:00, 04:00 … instead of drifting. (A free-running lattice would need an absolute anchor, which the language does not yet carry.)

!12/25 and ! 12/25 are different

The separator is load-bearing:

• !12/25 (no space) — a field exclusion: the 25th of any month except December.
• ! 12/25 (set off by a separator) — a pattern exclusion: skip December 25 entirely.

It’s a membership test, not a generator with a count

isnow answers “does it hold now?” next and prev are derived from that and are unbounded. There is no “run exactly 10 times”: COUNT needs an anchor the language does not yet have. If you need a fixed, counted series, reach for iCalendar and gate it with isnow.

Defaults fill by position, not by intent

A lone 6 is exactly 06:00:00, not “6-ish.” A bare numeric weekday is legal only in the explicit three-group form (*/*/* 3 *:*:*), and there 3 is a weekday (Sunday = 1), not “the 3rd of the month.” The shorthand ladder resolves every short form by separator position — isnow canon makes it explicit.