Regex pattern for Temporal.PlainYearMonth ISO 8601 strings (e.g. 2023-01).
Validates month (01–12).
Under a non-ISO calendar toJSON() emits a full reference date rather than
YYYY-MM (e.g. 2022-12-25[u-ca=hebrew]), so that form is accepted too —
but only with the calendar annotation present, so a bare 2023-01-15 is
still rejected.
Regex pattern for Temporal.PlainYearMonth ISO 8601 strings (e.g.
2023-01). Validates month (01–12).Under a non-ISO calendar
toJSON()emits a full reference date rather thanYYYY-MM(e.g.2022-12-25[u-ca=hebrew]), so that form is accepted too — but only with the calendar annotation present, so a bare2023-01-15is still rejected.