@burglekitt/gmt/dist/regex/calendar-date.js

Temporal-based date and time utilities with timezone support and polyfill integration

// GMT's own calendar-annotated PlainDate string: the calendar-native year/month/day
// (e.g. Hebrew year 5785), tagged with the calendar identifier — not Temporal's own
// `[u-ca=...]` annotation convention, which keeps the ISO/proleptic-Gregorian digits and
// only tags the calendar. See convertDateToCalendar for the rationale.
//
// The optional trailing `;era=<name>` captures an era identifier (e.g. "reiwa"), needed
// only for the "japanese" calendar: unlike every other supported calendar, Temporal's
// `.year` for "japanese" stays proleptic (does not reset at an era change), so the
// era-relative year (Temporal's `.eraYear`) has to be paired with the era name to be
// unambiguous. See formatCalendarDate/parseCalendarDateValue for how it round-trips.
export const calendarDate = /^(\d{4,6})-(\d{2})-(\d{2})\[u-ca=([a-z][a-z0-9-]*)(?:;era=([a-z]+))?\]$/;