# @northguild/gmt > Temporal-first date and time utilities with timezone support and polyfill integration. ## Reference - [API reference](https://northguild.dev/gmt/reference.md): Index of every namespace, with links to each module and to the shared types. ## Reference — calendar - [addOperatingTime](https://northguild.dev/gmt/reference/calendar/hours/addOperatingTime.md): Return the instant at which `duration` of open time has elapsed since `start`: the deadline of a service level measured in working hours. - [bucketRange](https://northguild.dev/gmt/reference/calendar/calculate/bucketRange.md): Return the start instant of every `unit` bucket the half-open range `[start, end)` touches, bucketed **in `timeZone`**. - [buildBusinessCalendar](https://northguild.dev/gmt/reference/calendar/rules/buildBusinessCalendar.md): Expand holiday rules into a `BusinessCalendar` for a range of years. - [businessDaysBetween](https://northguild.dev/gmt/reference/calendar/business/businessDaysBetween.md): Count the working days between two local dates, **excluding `start` and including `end`**. - [easterSunday](https://northguild.dev/gmt/reference/calendar/rules/easterSunday.md): Easter Sunday of a year as an ISO date, by the Gregorian computus unless the Julian one is asked for. - [floorToZone](https://northguild.dev/gmt/reference/calendar/calculate/floorToZone.md): Floor an instant to the start of the `unit` containing it **in `timeZone`**, and return the instant of that boundary. - [getFiscalPeriod](https://northguild.dev/gmt/reference/calendar/calculate/getFiscalPeriod.md): Return the fiscal year, period and week `value` falls in, for a 52/53-week retail calendar. - [getIsoWeekDate](https://northguild.dev/gmt/reference/calendar/calculate/getIsoWeekDate.md): Return the ISO 8601 week date — week-numbering year, week and weekday — for `value`. - [getOrdinalDate](https://northguild.dev/gmt/reference/calendar/calculate/getOrdinalDate.md): Return the ISO 8601 ordinal date — calendar year and day of year — for `value`. - [getQuarter](https://northguild.dev/gmt/reference/calendar/calculate/getQuarter.md): Return the quarter `value` falls in, as a year and a quarter number. - [holidayDates](https://northguild.dev/gmt/reference/calendar/rules/holidayDates.md): Every date a holiday rule produces in an ISO year, as sorted ISO PlainDate strings. - [isOpenAt](https://northguild.dev/gmt/reference/calendar/hours/isOpenAt.md): Return true when `schedule` is open at the instant `isoString`. - [isValidBusinessCalendar](https://northguild.dev/gmt/reference/calendar/validate/isValidBusinessCalendar.md): Return true when `calendar` is a `BusinessCalendar` the business-day functions accept. - [isValidFiscalCalendar](https://northguild.dev/gmt/reference/calendar/validate/isValidFiscalCalendar.md): Return true when `calendar` is a `FiscalCalendar` that `getFiscalPeriod` accepts. - [isValidFiscalExtraWeek](https://northguild.dev/gmt/reference/calendar/validate/isValidFiscalExtraWeek.md): Return true when `value` is a valid FiscalExtraWeek: the period a 53rd week is added to. - [isValidFiscalPattern](https://northguild.dev/gmt/reference/calendar/validate/isValidFiscalPattern.md): Return true when `pattern` is a valid FiscalPattern. - [isValidFiscalYearLabel](https://northguild.dev/gmt/reference/calendar/validate/isValidFiscalYearLabel.md): Return true when `value` is a valid FiscalYearLabel: the rule that picks the calendar year naming a fiscal year. - [isValidHolidayRule](https://northguild.dev/gmt/reference/calendar/validate/isValidHolidayRule.md): Return true when `rule` is a `HolidayRule` that `holidayDates` and `buildBusinessCalendar` accept. It answers "is this a rule", which `holidayDates` cannot: that returns `[]` both for an invalid rule and for a year with no occurrence. - [isValidRollConvention](https://northguild.dev/gmt/reference/calendar/validate/isValidRollConvention.md): Return true when `convention` is a `RollConvention` that `rollDate` implements. - [isValidZoneBucketUnit](https://northguild.dev/gmt/reference/calendar/validate/isValidZoneBucketUnit.md): Return true when `unit` is a valid ZoneBucketUnit. - [mergeCalendars](https://northguild.dev/gmt/reference/calendar/business/mergeCalendars.md): Compose several jurisdictions' calendars into one whose working days are those they all share. - [nextBusinessDay](https://northguild.dev/gmt/reference/calendar/business/nextBusinessDay.md): Return the first working day **strictly after** `value`. - [nextCloseAt](https://northguild.dev/gmt/reference/calendar/hours/nextCloseAt.md): Return the first instant at or after `isoString` that `schedule` is closed, as a UTC instant. - [nextOpenAt](https://northguild.dev/gmt/reference/calendar/hours/nextOpenAt.md): Return the first instant at or after `isoString` that `schedule` is open, as a UTC instant. - [nthWeekdayOfMonth](https://northguild.dev/gmt/reference/calendar/rules/nthWeekdayOfMonth.md): The `n`-th `weekday` of a month, counted from the start (`1` to `5`) or from the end (`-1` to `-5`; `"last"` is `-1`), as RFC 5545 §3.3.10 counts a `BYDAY` ordinal in a monthly rule. - [observedDate](https://northguild.dev/gmt/reference/calendar/rules/observedDate.md): Where a holiday is observed under a policy. The policy is required and has no default: every default would make some other calendar wrong. - [operatingIntervals](https://northguild.dev/gmt/reference/calendar/hours/operatingIntervals.md): Return the instants an `OperatingSchedule` is open inside `range`: its weekly windows with holidays closed and overrides applied, resolved in the schedule's zone. - [operatingTimeBetween](https://northguild.dev/gmt/reference/calendar/hours/operatingTimeBetween.md): Return how much open time `schedule` has between two instants, as an exact ISO duration. - [previousBusinessDay](https://northguild.dev/gmt/reference/calendar/business/previousBusinessDay.md): Return the last working day **strictly before** `value`. - [recurringWindows](https://northguild.dev/gmt/reference/calendar/hours/recurringWindows.md): Return the instants a weekly pattern of local windows is open inside `range`, read in `timeZone`: the primitive under operating hours, curfews and recurring crew windows. - [rollDate](https://northguild.dev/gmt/reference/calendar/business/rollDate.md): Move a local date onto a working day according to `convention`. ## Reference — duration - [absDuration](https://northguild.dev/gmt/reference/duration/calculate/absDuration.md): Return the absolute value of an ISO 8601 duration string. - [addDuration](https://northguild.dev/gmt/reference/duration/calculate/addDuration.md): Combine two ISO 8601 duration strings by addition. - [compareDurations](https://northguild.dev/gmt/reference/duration/compare/compareDurations.md): Compare two ISO 8601 duration strings by length. - [durationFromUnits](https://northguild.dev/gmt/reference/duration/calculate/durationFromUnits.md): Write an amount given as a unit object, such as `{ minutes: 15 }`, as an ISO 8601 duration string. - [formatDuration](https://northguild.dev/gmt/reference/duration/format/formatDuration.md): Render an ISO 8601 duration string as a locale-aware, human-readable string. - [formatHumanDuration](https://northguild.dev/gmt/reference/duration/format/formatHumanDuration.md): Write an ISO 8601 duration in the compact form `parseHumanDuration` reads, such as `2h 30m`. - [getDurationSign](https://northguild.dev/gmt/reference/duration/calculate/getDurationSign.md): Report whether an ISO 8601 duration is negative, zero-length, or positive. - [getDurationUnit](https://northguild.dev/gmt/reference/duration/calculate/getDurationUnit.md): Read a single component out of an ISO 8601 duration string. - [isValidDuration](https://northguild.dev/gmt/reference/duration/validate/isValidDuration.md): Return true if `value` is a valid ISO 8601 duration string. - [negateDuration](https://northguild.dev/gmt/reference/duration/calculate/negateDuration.md): Flip the sign of an ISO 8601 duration string. - [normalizeDuration](https://northguild.dev/gmt/reference/duration/normalize/normalizeDuration.md): Roll an ISO 8601 duration string's small units into larger ones. - [parseDuration](https://northguild.dev/gmt/reference/duration/parse/parseDuration.md): Parse and re-normalize an ISO 8601 duration string. - [parseHumanDuration](https://northguild.dev/gmt/reference/duration/parse/parseHumanDuration.md): Read a duration written the way people write it, such as `2h 30m`, `1.5h` or `3 days`, into an ISO 8601 duration string. - [subtractDuration](https://northguild.dev/gmt/reference/duration/calculate/subtractDuration.md): Combine two ISO 8601 duration strings by subtraction. - [totalDuration](https://northguild.dev/gmt/reference/duration/calculate/totalDuration.md): Express an ISO 8601 duration as a single fractional total in one unit. - [totalUnits](https://northguild.dev/gmt/reference/duration/calculate/totalUnits.md): Express an amount written as a unit object, such as `{ minutes: 15 }`, as a single fractional total in one unit. ## Reference — gnss - [gnssToUtc](https://northguild.dev/gmt/reference/gnss/convert/gnssToUtc.md): Convert a satellite system's time-scale string to a UTC instant string. - [gnssWeekToUtc](https://northguild.dev/gmt/reference/gnss/convert/gnssWeekToUtc.md): Convert a week number and time of week, as a receiver reports them, to a UTC instant string. - [rinexWeekToUtc](https://northguild.dev/gmt/reference/gnss/convert/rinexWeekToUtc.md): Convert a week number from a RINEX navigation file, and the seconds of that week, to a UTC instant string. - [utcToGnss](https://northguild.dev/gmt/reference/gnss/convert/utcToGnss.md): Convert a UTC instant to a satellite system's own time, as a time-scale string. - [utcToGnssWeek](https://northguild.dev/gmt/reference/gnss/convert/utcToGnssWeek.md): Return the week, time of week and era of a UTC instant on a satellite week counter. - [utcToRinexWeek](https://northguild.dev/gmt/reference/gnss/convert/utcToRinexWeek.md): Return the RINEX navigation-file week and seconds of week of a UTC instant. ## Reference — instant - [classifyLocal](https://northguild.dev/gmt/reference/instant/convert/classifyLocal.md): Report whether a zoneless local wall time is unique, ambiguous or nonexistent in a zone — before any policy resolves it. - [fromOffsetInstant](https://northguild.dev/gmt/reference/instant/convert/fromOffsetInstant.md): Render an instant-plus-offset pair back to the local time it describes. - [isValidUtcOffset](https://northguild.dev/gmt/reference/instant/validate/isValidUtcOffset.md): Return true when `value` is a UTC offset in the form the offset-instant pair stores: ISO 8601 extended `±HH:MM`, optionally `±HH:MM:SS`. - [OffsetInstant](https://northguild.dev/gmt/reference/types/OffsetInstant.md): An absolute instant paired with the local UTC offset in force where the event happened. - [resolveLocal](https://northguild.dev/gmt/reference/instant/convert/resolveLocal.md): Resolve a zoneless local wall time in a time zone and return the instant it names. - [toOffsetInstant](https://northguild.dev/gmt/reference/instant/convert/toOffsetInstant.md): Split an ISO 8601 instant string into the instant-plus-offset pair the world exchanges. ## Reference — intermodal - [billingTimeline](https://northguild.dev/gmt/reference/intermodal/calculate/billingTimeline.md): Lay out the deadline chain around a demurrage or detention invoice: the last date it may be issued, the last date it may be disputed, and the last date the dispute must be resolved. - [bolTimestamp](https://northguild.dev/gmt/reference/intermodal/format/bolTimestamp.md): Render an instant as the date a bill of lading carries for an event: the calendar date on the local clock where the event happened. - [chargeableDays](https://northguild.dev/gmt/reference/intermodal/calculate/chargeableDays.md): Count the days a container is charged for between the start of its clock and its exit, and list the dates behind the count. - [classifyEdifactDtmFormat](https://northguild.dev/gmt/reference/intermodal/parse/classifyEdifactDtmFormat.md): Name the kind of value a UN/EDIFACT data element 2379 format code states, and return the code narrowed to that kind, so a code that arrives as data reaches the function that reads it. - [classifyX12DateTimePeriodFormat](https://northguild.dev/gmt/reference/intermodal/parse/classifyX12DateTimePeriodFormat.md): Name the kind of value an X12 data element 1250 format qualifier states, and return the code narrowed to that kind, so a code that arrives as data reaches the function that reads it. - [classifyX12TimeCode](https://northguild.dev/gmt/reference/intermodal/parse/classifyX12TimeCode.md): Say whether an X12 time code (data element 623) states an offset or names a zone, and return the code narrowed to the function that reads it. - [demurrageClock](https://northguild.dev/gmt/reference/intermodal/calculate/demurrageClock.md): Pick the two events a charge's clock runs between. - [formatEdifactDate](https://northguild.dev/gmt/reference/intermodal/format/formatEdifactDate.md): Write an ISO 8601 date as a UN/EDIFACT `DTM` value (data element 2380) in a date format code (data element 2379). The inverse of `parseEdifactDate`: what one writes, the other reads back. - [formatEdifactDatePeriod](https://northguild.dev/gmt/reference/intermodal/format/formatEdifactDatePeriod.md): Write two ISO 8601 dates as a UN/EDIFACT `DTM` period (data element 2380) in a date period format code (data element 2379). The inverse of `parseEdifactDatePeriod`. - [formatEdifactDateTime](https://northguild.dev/gmt/reference/intermodal/format/formatEdifactDateTime.md): Write an ISO 8601 local date-time as a UN/EDIFACT `DTM` value (data element 2380) in a format code with no offset (data element 2379). The inverse of `parseEdifactDateTime`. - [formatEdifactDateTimePeriod](https://northguild.dev/gmt/reference/intermodal/format/formatEdifactDateTimePeriod.md): Write two ISO 8601 local date-times as a UN/EDIFACT `DTM` period (data element 2380) in a date-time period format code (data element 2379). The inverse of `parseEdifactDateTimePeriod`. - [formatEdifactOffsetDateTime](https://northguild.dev/gmt/reference/intermodal/format/formatEdifactOffsetDateTime.md): Write an ISO 8601 date-time with an offset as a UN/EDIFACT `DTM` value (data element 2380) in a format code that carries an offset (data element 2379). The inverse of `parseEdifactOffsetDateTime`. - [formatEdifactTime](https://northguild.dev/gmt/reference/intermodal/format/formatEdifactTime.md): Write an ISO 8601 time as a UN/EDIFACT `DTM` value (data element 2380) in a time format code (data element 2379). The inverse of `parseEdifactTime`. - [formatEpcisEvent](https://northguild.dev/gmt/reference/intermodal/format/formatEpcisEvent.md): Write an instant-plus-offset pair as the two required time fields of a GS1 EPCIS 2.0 event. - [formatX12Date](https://northguild.dev/gmt/reference/intermodal/format/formatX12Date.md): Write an ISO 8601 date as an X12 Date Time Period value (data element 1251) in a date format qualifier (data element 1250). The inverse of `parseX12Date`. - [formatX12DateRange](https://northguild.dev/gmt/reference/intermodal/format/formatX12DateRange.md): Write two ISO 8601 dates as an X12 Date Time Period range (data element 1251) in a date range format qualifier (data element 1250). The inverse of `parseX12DateRange`. - [formatX12DateTime](https://northguild.dev/gmt/reference/intermodal/format/formatX12DateTime.md): Write an ISO 8601 local date-time as an X12 Date Time Period value (data element 1251) in a date-time format qualifier (data element 1250). The inverse of `parseX12DateTime`. - [formatX12DateTimeRange](https://northguild.dev/gmt/reference/intermodal/format/formatX12DateTimeRange.md): Write two ISO 8601 local date-times as an X12 Date Time Period range (data element 1251) in a date-time range format qualifier (data element 1250). The inverse of `parseX12DateTimeRange`. - [formatX12Time](https://northguild.dev/gmt/reference/intermodal/format/formatX12Time.md): Write an ISO 8601 time as an X12 time in a time format qualifier (data element 1250). The result is also a data element 337 (Time) value: `parseX12Time` reads it back with the same qualifier, and with none. - [formatX12TimeElement](https://northguild.dev/gmt/reference/intermodal/format/formatX12TimeElement.md): Write an ISO 8601 time as an X12 data element 337 (Time) value, in the form the caller names by the element's own mask. `parseX12Time` reads the result back when it is given no qualifier. - [freeTimeExpiry](https://northguild.dev/gmt/reference/intermodal/calculate/freeTimeExpiry.md): Lay out a container's free time from the instant its clock started, and say when it ends. - [isValidEdifactDate](https://northguild.dev/gmt/reference/intermodal/validate/isValidEdifactDate.md): Return true when `value` is a UN/EDIFACT `DTM` value (data element 2380) that states a real calendar date in a date format code (data element 2379). - [isValidEdifactDatePeriod](https://northguild.dev/gmt/reference/intermodal/validate/isValidEdifactDatePeriod.md): Return true when `value` is a UN/EDIFACT `DTM` value (data element 2380) that states a period between two real calendar dates, in a date period format code (data element 2379). - [isValidEdifactDateTime](https://northguild.dev/gmt/reference/intermodal/validate/isValidEdifactDateTime.md): Return true when `value` is a UN/EDIFACT `DTM` value (data element 2380) that states a real date and time in a format code with no offset (data element 2379). - [isValidEdifactDateTimePeriod](https://northguild.dev/gmt/reference/intermodal/validate/isValidEdifactDateTimePeriod.md): Return true when `value` is a UN/EDIFACT `DTM` value (data element 2380) that states a period between two real local date-times, in a date-time period format code (data element 2379). - [isValidEdifactDtmFormat](https://northguild.dev/gmt/reference/intermodal/validate/isValidEdifactDtmFormat.md): Return true when `format` is a UN/EDIFACT data element 2379 format code that the EDIFACT functions read and write. - [isValidEdifactOffsetDateTime](https://northguild.dev/gmt/reference/intermodal/validate/isValidEdifactOffsetDateTime.md): Return true when `value` is a UN/EDIFACT `DTM` value (data element 2380) that states a real date and time with an offset from UTC, in a format code that carries one (data element 2379). - [isValidEdifactTime](https://northguild.dev/gmt/reference/intermodal/validate/isValidEdifactTime.md): Return true when `value` is a UN/EDIFACT `DTM` value (data element 2380) that states a real time of day in a time format code (data element 2379). - [isValidEpcisEvent](https://northguild.dev/gmt/reference/intermodal/validate/isValidEpcisEvent.md): Validate whether a value carries the two required time fields of a GS1 EPCIS 2.0 event, each in the grammar GS1 publishes for it. - [isValidEpcisEventTime](https://northguild.dev/gmt/reference/intermodal/validate/isValidEpcisEventTime.md): Return true when `value` is a real GS1 EPCIS 2.0 `eventTime`: the moment a supply-chain event happened, written as a date and time with `Z` or a UTC offset. - [isValidEpcisTimeZoneOffset](https://northguild.dev/gmt/reference/intermodal/validate/isValidEpcisTimeZoneOffset.md): Return true when `value` is a GS1 EPCIS 2.0 `eventTimeZoneOffset`: the UTC offset the local clock ran at where a supply-chain event happened, written `±HH:MM`. - [isValidX12Date](https://northguild.dev/gmt/reference/intermodal/validate/isValidX12Date.md): Return true when `value` is an X12 Date Time Period value (data element 1251) that states a real calendar date in a date format qualifier (data element 1250). - [isValidX12DateAndTime](https://northguild.dev/gmt/reference/intermodal/validate/isValidX12DateAndTime.md): Return true when the date and the time of an X12 segment, sent as two elements, together state a real local date and time. - [isValidX12DateRange](https://northguild.dev/gmt/reference/intermodal/validate/isValidX12DateRange.md): Return true when `value` is an X12 Date Time Period value (data element 1251) that states a range between two real calendar dates, in a date range format qualifier (data element 1250). - [isValidX12DateTime](https://northguild.dev/gmt/reference/intermodal/validate/isValidX12DateTime.md): Return true when `value` is an X12 Date Time Period value (data element 1251) that states a real date and time in a date-time format qualifier (data element 1250). - [isValidX12DateTimePeriodFormat](https://northguild.dev/gmt/reference/intermodal/validate/isValidX12DateTimePeriodFormat.md): Return true when `format` is an X12 data element 1250 (Date Time Period Format Qualifier) code that the X12 functions read and write. - [isValidX12DateTimeRange](https://northguild.dev/gmt/reference/intermodal/validate/isValidX12DateTimeRange.md): Return true when `value` is an X12 Date Time Period value (data element 1251) that states a range between two real local date-times, in a date-time range format qualifier (data element 1250). - [isValidX12Time](https://northguild.dev/gmt/reference/intermodal/validate/isValidX12Time.md): Return true when `value` is an X12 time that states a real time of day: a data element 337 value with no qualifier, or a time that fits the data element 1250 format qualifier it arrived with. - [isValidX12TimeCode](https://northguild.dev/gmt/reference/intermodal/validate/isValidX12TimeCode.md): Return true when `timeCode` is one of the 56 X12 data element 623 time codes, the codes `x12TimeCodeOffset` and `x12TimeCodeZone` read between them. - [multimodalETA](https://northguild.dev/gmt/reference/intermodal/calculate/multimodalETA.md): Compute an end-to-end ETA across the legs of a multimodal move, and report the time in transit and the time in dwell separately. - [parseEdifactDate](https://northguild.dev/gmt/reference/intermodal/parse/parseEdifactDate.md): Parse a UN/EDIFACT `DTM` value that states a calendar date, as an ISO 8601 date. - [parseEdifactDatePeriod](https://northguild.dev/gmt/reference/intermodal/parse/parseEdifactDatePeriod.md): Parse a UN/EDIFACT `DTM` value that states a period between two calendar dates, as its start and end. - [parseEdifactDateTime](https://northguild.dev/gmt/reference/intermodal/parse/parseEdifactDateTime.md): Parse a UN/EDIFACT `DTM` value that states a date and a time with no offset, as an ISO 8601 local date-time. - [parseEdifactDateTimePeriod](https://northguild.dev/gmt/reference/intermodal/parse/parseEdifactDateTimePeriod.md): Parse a UN/EDIFACT `DTM` value that states a period between two local date-times, as its start and end. - [parseEdifactOffsetDateTime](https://northguild.dev/gmt/reference/intermodal/parse/parseEdifactOffsetDateTime.md): Parse a UN/EDIFACT `DTM` value that states a date and a time with an offset from UTC, as an ISO 8601 date-time with its offset. - [parseEdifactTime](https://northguild.dev/gmt/reference/intermodal/parse/parseEdifactTime.md): Parse a UN/EDIFACT `DTM` value that states a time of day, as an ISO 8601 time. - [parseEpcisEvent](https://northguild.dev/gmt/reference/intermodal/parse/parseEpcisEvent.md): Read the two required time fields of a GS1 EPCIS 2.0 event as an instant, the UTC offset in force where the event happened, and the local wall clock there. - [parseX12Date](https://northguild.dev/gmt/reference/intermodal/parse/parseX12Date.md): Parse an X12 Date Time Period value that states a calendar date, as an ISO 8601 date. - [parseX12DateAndTime](https://northguild.dev/gmt/reference/intermodal/parse/parseX12DateAndTime.md): Read the date and the time of an X12 segment, sent as two elements, as one ISO 8601 local date-time. - [parseX12DateRange](https://northguild.dev/gmt/reference/intermodal/parse/parseX12DateRange.md): Parse an X12 Date Time Period value that states a range between two calendar dates, as its start and end. - [parseX12DateTime](https://northguild.dev/gmt/reference/intermodal/parse/parseX12DateTime.md): Parse an X12 Date Time Period value that states a date and a time, as an ISO 8601 local date-time. - [parseX12DateTimeRange](https://northguild.dev/gmt/reference/intermodal/parse/parseX12DateTimeRange.md): Parse an X12 Date Time Period value that states a range between two local date-times, as its start and end. - [parseX12Time](https://northguild.dev/gmt/reference/intermodal/parse/parseX12Time.md): Parse an X12 time as an ISO 8601 time: a data element 337 value with no qualifier, or a time that arrives with a data element 1250 format qualifier. - [x12TimeCodeOffset](https://northguild.dev/gmt/reference/intermodal/parse/x12TimeCodeOffset.md): Read the UTC offset an X12 time code (data element 623) states. - [x12TimeCodeZone](https://northguild.dev/gmt/reference/intermodal/parse/x12TimeCodeZone.md): Read the zone an X12 time code (data element 623) names. ## Reference — interval - [clampInterval](https://northguild.dev/gmt/reference/interval/calculate/clampInterval.md): Return the part of `interval` that lies inside `bounds`, or null when none of it does. - [intersectIntervals](https://northguild.dev/gmt/reference/interval/calculate/intersectIntervals.md): Return the half-open interval two intervals share, or null when they share no instant. - [intervalContains](https://northguild.dev/gmt/reference/interval/compare/intervalContains.md): Return true when an ISO 8601 instant string lies inside a half-open interval. - [intervalsOverlap](https://northguild.dev/gmt/reference/interval/compare/intervalsOverlap.md): Return true when two half-open intervals share at least one instant. - [isValidInterval](https://northguild.dev/gmt/reference/interval/validate/isValidInterval.md): Validate whether a value is an `Interval` the `interval/` namespace accepts. - [mergeIntervals](https://northguild.dev/gmt/reference/interval/calculate/mergeIntervals.md): Collapse a list of half-open intervals into the fewest sorted, non-overlapping intervals. - [splitIntervalAt](https://northguild.dev/gmt/reference/interval/calculate/splitIntervalAt.md): Split a half-open interval at instant boundaries into consecutive half-open pieces. - [subtractIntervals](https://northguild.dev/gmt/reference/interval/calculate/subtractIntervals.md): Return the parts of `from` that no interval in `remove` covers, as sorted half-open intervals. - [sumIntervals](https://northguild.dev/gmt/reference/interval/calculate/sumIntervals.md): Return the time covered by a list of half-open intervals, as an exact ISO 8601 duration. ## Reference — plain - [addBusinessDays](https://northguild.dev/gmt/reference/plain/calculate/addBusinessDays.md): Return a PlainDate ISO string with `amount` working days added to `value`. - [addDate](https://northguild.dev/gmt/reference/plain/calculate/addDate.md): Return a PlainDate ISO string with `amount` added according to `units`. - [addDateTime](https://northguild.dev/gmt/reference/plain/calculate/addDateTime.md): Return a PlainDateTime ISO string with `units` added to `value`. - [addTime](https://northguild.dev/gmt/reference/plain/calculate/addTime.md): Return a PlainTime ISO string with `units` added to `value`. - [areDatesEqual](https://northguild.dev/gmt/reference/plain/compare/areDatesEqual.md): Compare two ISO date-like strings for equality, ignoring time components. - [areDatesEqualBy](https://northguild.dev/gmt/reference/plain/compare/areDatesEqualBy.md): Compare two ISO date strings for equality at a given calendar unit. - [areDateTimesEqual](https://northguild.dev/gmt/reference/plain/compare/areDateTimesEqual.md): Return true if two PlainDateTime ISO strings represent the same instant of local date/time components. - [areDateTimesEqualBy](https://northguild.dev/gmt/reference/plain/compare/areDateTimesEqualBy.md): Compare two ISO datetime strings for equality at a given unit. - [areTimesEqual](https://northguild.dev/gmt/reference/plain/compare/areTimesEqual.md): Return true if two PlainTime ISO strings represent the same time components. - [chopDate](https://northguild.dev/gmt/reference/plain/chop/chopDate.md): Return the PlainTime portion extracted from an ISO PlainDateTime string. - [chopMilliseconds](https://northguild.dev/gmt/reference/plain/chop/chopMilliseconds.md): Return a string with millisecond precision removed from a PlainDateTime or PlainTime value. - [chopSeconds](https://northguild.dev/gmt/reference/plain/chop/chopSeconds.md): Return an ISO string with second precision removed from a PlainDateTime or PlainTime value. - [chopTime](https://northguild.dev/gmt/reference/plain/chop/chopTime.md): Return the PlainDate portion extracted from an ISO PlainDateTime string. - [clampDate](https://northguild.dev/gmt/reference/plain/calculate/clampDate.md): Restrict `value` to the range [`min`, `max`]. - [closestDateTo](https://northguild.dev/gmt/reference/plain/calculate/closestDateTo.md): Return the candidate date nearest to `target` by calendar distance. - [convertDateToCalendar](https://northguild.dev/gmt/reference/plain/convert/convertDateToCalendar.md): Express a PlainDate in a calendar system: the RFC 9557 string `Temporal.PlainDate#toString()` writes for that date in that calendar. - [cycleDate](https://northguild.dev/gmt/reference/plain/calculate/cycleDate.md): Return a PlainDate ISO string with `field` cycled by `amount`, wrapping at that field's own min/max instead of carrying into the next larger field. - [cycleDateTime](https://northguild.dev/gmt/reference/plain/calculate/cycleDateTime.md): Return a PlainDateTime ISO string with `field` cycled by `amount`, wrapping at that field's own min/max instead of carrying into the next larger field. - [cycleTime](https://northguild.dev/gmt/reference/plain/calculate/cycleTime.md): Return a PlainTime ISO string with `field` cycled by `amount`, wrapping at that field's own min/max instead of carrying into the next larger field (`hour` 23 `+1` wraps to `0`, it never changes a date — `cycleTime` has no date component to carry into in the first place). - [diffDate](https://northguild.dev/gmt/reference/plain/calculate/diffDate.md): Return the difference between two PlainDate values using the provided `unit`. - [diffDateAsDuration](https://northguild.dev/gmt/reference/plain/calculate/diffDateAsDuration.md): Return the difference between two PlainDate values as an ISO 8601 duration string, bridging to the `duration` namespace (see `parseDuration`, `normalizeDuration`). - [diffDateTime](https://northguild.dev/gmt/reference/plain/calculate/diffDateTime.md): Return the difference between two PlainDateTime values in the requested unit. - [diffDateTimeAsDuration](https://northguild.dev/gmt/reference/plain/calculate/diffDateTimeAsDuration.md): Return the difference between two PlainDateTime values as an ISO 8601 duration string, bridging to the `duration` namespace (see `parseDuration`, `normalizeDuration`). - [diffTime](https://northguild.dev/gmt/reference/plain/calculate/diffTime.md): Return the difference between two PlainTime values in the requested unit. - [endOfDate](https://northguild.dev/gmt/reference/plain/calculate/endOfDate.md): Return the end of the specified date `unit` for a given ISO 8601 date string. - [endOfDateTime](https://northguild.dev/gmt/reference/plain/calculate/endOfDateTime.md): Return the end of the specified date-time `unit` for a given ISO 8601 datetime string. - [endOfQuarterForDate](https://northguild.dev/gmt/reference/plain/calculate/endOfQuarterForDate.md): Return the last day of the quarter for a given ISO date. - [endOfQuarterForDateTime](https://northguild.dev/gmt/reference/plain/calculate/endOfQuarterForDateTime.md): Return the end of the quarter for a given ISO datetime. - [endOfTime](https://northguild.dev/gmt/reference/plain/calculate/endOfTime.md): Return the end of the specified time `unit` for a given ISO 8601 time string. - [formatCalendar](https://northguild.dev/gmt/reference/plain/format/formatCalendar.md): Format a plain date-time as a relative day label plus time-of-day, e.g. "Tomorrow at 2:30 PM". The `formatRelativeDateTime` family does not cover this: it renders "in 1 day", an elapsed-time phrase, not a day label + clock time. - [formatDate](https://northguild.dev/gmt/reference/plain/format/formatDate.md): Return a localized string for a PlainDate ISO input using Intl options. - [formatDateRange](https://northguild.dev/gmt/reference/plain/format/formatDateRange.md): Format a plain date range using the Temporal Intl.DateTimeFormat formatRange API. - [formatDateTime](https://northguild.dev/gmt/reference/plain/format/formatDateTime.md): Return a localized string for a PlainDateTime ISO input using Intl options. - [formatDateTimeRange](https://northguild.dev/gmt/reference/plain/format/formatDateTimeRange.md): Format a plain datetime range using the Temporal Intl.DateTimeFormat formatRange API. - [formatDateTimeToParts](https://northguild.dev/gmt/reference/plain/format/formatDateTimeToParts.md): Return the locale-formatted parts of a PlainDateTime. - [formatDateToParts](https://northguild.dev/gmt/reference/plain/format/formatDateToParts.md): Return the locale-formatted parts of a PlainDate. - [formatRelativeDate](https://northguild.dev/gmt/reference/plain/format/formatRelativeDate.md): Format the relative time between a plain date and a reference date. - [formatRelativeDateTime](https://northguild.dev/gmt/reference/plain/format/formatRelativeDateTime.md): Format the relative time between a plain date-time and a reference date-time. - [formatRelativeTime](https://northguild.dev/gmt/reference/plain/format/formatRelativeTime.md): Format the relative time between a plain time and a reference time. - [formatSqlDateTime](https://northguild.dev/gmt/reference/plain/format/formatSqlDateTime.md): Format a plain ISO 8601 datetime string as a SQL timestamp literal without a time zone — the `YYYY-MM-DD HH:MM:SS[.fff]` form of standard SQL `TIMESTAMP` and MySQL/SQLite `DATETIME` columns. - [formatTime](https://northguild.dev/gmt/reference/plain/format/formatTime.md): Return a localized string for a PlainTime ISO input using Intl options. - [getDay](https://northguild.dev/gmt/reference/plain/get/getDay.md): Return the current day of month using the system timeZone. - [getDayOfWeek](https://northguild.dev/gmt/reference/plain/get/getDayOfWeek.md): Return the current ISO day of the week as a number in the system timeZone. - [getDayOfYear](https://northguild.dev/gmt/reference/plain/calculate/getDayOfYear.md): Return the ordinal day-of-year (1-based) for `value`. - [getDaysInMonth](https://northguild.dev/gmt/reference/plain/calculate/getDaysInMonth.md): Return the number of days in the month containing `value`. - [getDaysInYear](https://northguild.dev/gmt/reference/plain/calculate/getDaysInYear.md): Return the number of days in the calendar year containing `value`. - [getHour](https://northguild.dev/gmt/reference/plain/get/getHour.md): Return the current hour using the system timeZone. - [getLargestDateDurationUnit](https://northguild.dev/gmt/reference/plain/calculate/getLargestDateDurationUnit.md): Return the largest DateDurationUnit from the provided array. - [getLargestDateTimeDurationUnit](https://northguild.dev/gmt/reference/plain/calculate/getLargestDateTimeDurationUnit.md): Return the largest DateTimeDurationUnit from the provided array. - [getLargestTimeDurationUnit](https://northguild.dev/gmt/reference/plain/calculate/getLargestTimeDurationUnit.md): Return the largest TimeDurationUnit from the provided array. - [getLocaleDayOfWeek](https://northguild.dev/gmt/reference/plain/calculate/getLocaleDayOfWeek.md): Return the locale-relative day-of-week index for `value`. - [getLocaleEndOfWeek](https://northguild.dev/gmt/reference/plain/calculate/getLocaleEndOfWeek.md): Return the end of the week containing `value`, using `locale`'s first day of week (e.g. fr-FR: week ends Sunday, ja-JP: week ends Saturday). - [getLocaleEraNames](https://northguild.dev/gmt/reference/plain/locale/getLocaleEraNames.md): Return a locale's Gregorian era names as [BCE-label, CE-label]. - [getLocaleMeridiems](https://northguild.dev/gmt/reference/plain/locale/getLocaleMeridiems.md): Return a locale's AM/PM (day-period) labels as `[AM-label, PM-label]`. - [getLocaleMonthNames](https://northguild.dev/gmt/reference/plain/locale/getLocaleMonthNames.md): Return the 12 Gregorian calendar-month names for a locale, in calendar order (January first, December last — not alphabetical). - [getLocaleStartOfWeek](https://northguild.dev/gmt/reference/plain/calculate/getLocaleStartOfWeek.md): Return the start of the week containing `value`, using `locale`'s first day of week (e.g. fr-FR: Monday, ja-JP: Sunday). - [getLocaleWeekdayNames](https://northguild.dev/gmt/reference/plain/locale/getLocaleWeekdayNames.md): Return the 7 weekday names for a locale, ordered starting from the locale's first day of the week. - [getLocaleWeekYear](https://northguild.dev/gmt/reference/plain/calculate/getLocaleWeekYear.md): Return the locale-relative week-numbering year `value` belongs to, from `locale`'s first day of week and a minimal-days-in-first-week rule. - [getMicrosecond](https://northguild.dev/gmt/reference/plain/get/getMicrosecond.md): Return the current microsecond using the system timeZone. - [getMillisecond](https://northguild.dev/gmt/reference/plain/get/getMillisecond.md): Return the current millisecond using the system timeZone. - [getMinute](https://northguild.dev/gmt/reference/plain/get/getMinute.md): Return the current minute using the system timeZone. - [getMonth](https://northguild.dev/gmt/reference/plain/get/getMonth.md): Return the current month using the system timeZone. - [getNanosecond](https://northguild.dev/gmt/reference/plain/get/getNanosecond.md): Return the current nanosecond using the system timeZone. - [getNow](https://northguild.dev/gmt/reference/plain/get/getNow.md): Return the current local PlainDateTime as an ISO string using the system timeZone. - [getNowUnit](https://northguild.dev/gmt/reference/plain/get/getNowUnit.md): Return the requested current unit value using the system timeZone. - [getQuarterForDate](https://northguild.dev/gmt/reference/plain/calculate/getQuarterForDate.md): Return the quarter of the year (1-4) for a given ISO date. - [getQuarterForDateTime](https://northguild.dev/gmt/reference/plain/calculate/getQuarterForDateTime.md): Return the quarter of the year (1-4) for a given ISO datetime. - [getSecond](https://northguild.dev/gmt/reference/plain/get/getSecond.md): Return the current second using the system timeZone. - [getToday](https://northguild.dev/gmt/reference/plain/get/getToday.md): Return the current PlainDate as an ISO string in the system timeZone. - [getWeekNumber](https://northguild.dev/gmt/reference/plain/calculate/getWeekNumber.md): Calculate the week number based on configurable week start day. - [getWeekOfMonth](https://northguild.dev/gmt/reference/plain/calculate/getWeekOfMonth.md): Return the 1-based row `value` falls on within its month's calendar grid, using `locale`'s first day of week. - [getWeekOfYear](https://northguild.dev/gmt/reference/plain/get/getWeekOfYear.md): Get the ISO week number of the current date. - [getWeeksInLocaleWeekYear](https://northguild.dev/gmt/reference/plain/calculate/getWeeksInLocaleWeekYear.md): Return the number of weeks (52 or 53) in the locale week-numbering year containing `value`, from `locale`'s first day of week and a minimal-days-in-first-week rule. - [getWeeksInMonth](https://northguild.dev/gmt/reference/plain/calculate/getWeeksInMonth.md): Return the number of calendar-grid rows (4, 5, or 6) `value`'s month spans, using `locale`'s first day of week. - [getWeeksInYear](https://northguild.dev/gmt/reference/plain/calculate/getWeeksInYear.md): Return the number of ISO weeks (52 or 53) in the ISO week-numbering year containing `value`. - [getWeekYear](https://northguild.dev/gmt/reference/plain/calculate/getWeekYear.md): Return the ISO 8601 week-numbering year `value` belongs to. - [getYear](https://northguild.dev/gmt/reference/plain/get/getYear.md): Return the current year as a zero-padded string in the system timeZone. - [hasSecond60](https://northguild.dev/gmt/reference/plain/validate/hasSecond60.md): Return true if the provided ISO 8601 date-time or time string has a second-60 field. - [intervalAbutsDate](https://northguild.dev/gmt/reference/plain/interval/intervalAbutsDate.md): Return true when two half-open date intervals `[aStart, aEnd)` and `[bStart, bEnd)` are exactly adjacent — one ends where the other starts, so they share nothing and leave no gap. - [intervalAbutsDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalAbutsDateTime.md): Return true when two half-open datetime intervals `[aStart, aEnd)` and `[bStart, bEnd)` are exactly adjacent — one ends where the other starts, so they share nothing and leave no gap. - [intervalAbutsTime](https://northguild.dev/gmt/reference/plain/interval/intervalAbutsTime.md): Return true when two half-open time intervals `[aStart, aEnd)` and `[bStart, bEnd)` are exactly adjacent — one ends where the other starts, so they share nothing and leave no gap. - [intervalContainsDate](https://northguild.dev/gmt/reference/plain/interval/intervalContainsDate.md): Return true when `pointOrStart` lies in the half-open interval `[intervalStart, intervalEnd)` (3-arg), or when the inner interval `[innerStart, innerEnd)` lies within it (4-arg). - [intervalContainsDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalContainsDateTime.md): Return true when `pointOrStart` lies in the half-open interval `[intervalStart, intervalEnd)` (3-arg), or when the inner interval `[innerStart, innerEnd)` lies within it (4-arg). - [intervalContainsTime](https://northguild.dev/gmt/reference/plain/interval/intervalContainsTime.md): Return true when `pointOrStart` lies in the half-open interval `[intervalStart, intervalEnd)` (3-arg), or when the inner interval `[innerStart, innerEnd)` lies within it (4-arg). - [intervalCountDate](https://northguild.dev/gmt/reference/plain/interval/intervalCountDate.md): Count how many `unit` boundaries a date interval crosses. - [intervalCountDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalCountDateTime.md): Count how many `unit` boundaries a date-time interval crosses. - [intervalCountTime](https://northguild.dev/gmt/reference/plain/interval/intervalCountTime.md): Count how many `unit` boundaries a time interval crosses. - [intervalDifferenceDate](https://northguild.dev/gmt/reference/plain/interval/intervalDifferenceDate.md): Return the portion(s) of interval A not covered by interval B. - [intervalDifferenceDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalDifferenceDateTime.md): Return the portion(s) of interval A not covered by interval B. - [intervalDifferenceTime](https://northguild.dev/gmt/reference/plain/interval/intervalDifferenceTime.md): Return the portion(s) of interval A not covered by interval B. - [intervalDivideEquallyDate](https://northguild.dev/gmt/reference/plain/interval/intervalDivideEquallyDate.md): Split a date interval into `n` equal-length sub-intervals. - [intervalDivideEquallyDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalDivideEquallyDateTime.md): Split a datetime interval into `n` equal-length sub-intervals. - [intervalDivideEquallyTime](https://northguild.dev/gmt/reference/plain/interval/intervalDivideEquallyTime.md): Split a time interval into `n` equal-length sub-intervals. - [intervalEngulfsDate](https://northguild.dev/gmt/reference/plain/interval/intervalEngulfsDate.md): Return true when the half-open interval B `[bStart, bEnd)` lies within the half-open interval A `[aStart, aEnd)` — every day of B is also in A. - [intervalEngulfsDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalEngulfsDateTime.md): Return true when the half-open interval B `[bStart, bEnd)` lies within the half-open interval A `[aStart, aEnd)` — every moment of B is also in A. - [intervalEngulfsTime](https://northguild.dev/gmt/reference/plain/interval/intervalEngulfsTime.md): Return true when the half-open interval B `[bStart, bEnd)` lies within the half-open interval A `[aStart, aEnd)` — every clock time of B is also in A. - [intervalFromDurationDate](https://northguild.dev/gmt/reference/plain/interval/intervalFromDurationDate.md): Construct a date interval from a single point plus an ISO 8601 duration, anchored at either end. - [intervalFromDurationDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalFromDurationDateTime.md): Construct a datetime interval from a single point plus an ISO 8601 duration, anchored at either end. - [intervalFromDurationTime](https://northguild.dev/gmt/reference/plain/interval/intervalFromDurationTime.md): Construct a time interval from a single point plus an ISO 8601 duration, anchored at either end. - [intervalIntersectionDate](https://northguild.dev/gmt/reference/plain/interval/intervalIntersectionDate.md): Return the overlapping span of two date intervals, or null when they do not overlap. - [intervalIntersectionDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalIntersectionDateTime.md): Return the overlapping span of two datetime intervals, or null when they do not overlap. - [intervalIntersectionTime](https://northguild.dev/gmt/reference/plain/interval/intervalIntersectionTime.md): Return the overlapping span of two time intervals, or null when they do not overlap. - [intervalLengthDate](https://northguild.dev/gmt/reference/plain/interval/intervalLengthDate.md): Return the exact length of a date interval in `unit`, as a real (possibly fractional) number. - [intervalLengthDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalLengthDateTime.md): Return the exact length of a datetime interval in `unit`, as a real (possibly fractional) number. - [intervalLengthTime](https://northguild.dev/gmt/reference/plain/interval/intervalLengthTime.md): Return the exact length of a time interval in `unit`, as a real (possibly fractional) number. - [intervalOverlappingDaysDate](https://northguild.dev/gmt/reference/plain/interval/intervalOverlappingDaysDate.md): Return how many distinct calendar dates two date intervals share. - [intervalOverlappingDaysDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalOverlappingDaysDateTime.md): Return how many distinct calendar dates two datetime intervals share. - [intervalsOverlapDate](https://northguild.dev/gmt/reference/plain/interval/intervalsOverlapDate.md): Return true when the half-open date intervals `[aStart, aEnd)` and `[bStart, bEnd)` share at least one day. - [intervalsOverlapDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalsOverlapDateTime.md): Return true when the half-open datetime intervals `[aStart, aEnd)` and `[bStart, bEnd)` share at least one moment. - [intervalsOverlapTime](https://northguild.dev/gmt/reference/plain/interval/intervalsOverlapTime.md): Return true when the half-open time intervals `[aStart, aEnd)` and `[bStart, bEnd)` share at least one clock time. - [intervalSplitAtDate](https://northguild.dev/gmt/reference/plain/interval/intervalSplitAtDate.md): Split a date interval at arbitrary `points`, producing consecutive sub-intervals. - [intervalSplitAtDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalSplitAtDateTime.md): Split a datetime interval at arbitrary `points`, producing consecutive sub-intervals. - [intervalSplitAtTime](https://northguild.dev/gmt/reference/plain/interval/intervalSplitAtTime.md): Split a time interval at arbitrary `points`, producing consecutive sub-intervals. - [intervalUnionDate](https://northguild.dev/gmt/reference/plain/interval/intervalUnionDate.md): Return the combined span of two date intervals, or null when they are disjoint. - [intervalUnionDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalUnionDateTime.md): Return the combined span of two datetime intervals, or null when they are disjoint. - [intervalUnionTime](https://northguild.dev/gmt/reference/plain/interval/intervalUnionTime.md): Return the combined span of two time intervals, or null when they are disjoint. - [intervalXorAllDate](https://northguild.dev/gmt/reference/plain/interval/intervalXorAllDate.md): Return the symmetric difference across a list of date intervals — the set of dates covered by an odd number of the input intervals. - [intervalXorAllDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalXorAllDateTime.md): Return the symmetric difference across a list of datetime intervals — the set of instants covered by an odd number of the input intervals. - [intervalXorAllTime](https://northguild.dev/gmt/reference/plain/interval/intervalXorAllTime.md): Return the symmetric difference across a list of time intervals — the set of clock times covered by an odd number of the input intervals. - [intervalXorDate](https://northguild.dev/gmt/reference/plain/interval/intervalXorDate.md): Return the symmetric difference of two date intervals — time covered by exactly one interval. - [intervalXorDateTime](https://northguild.dev/gmt/reference/plain/interval/intervalXorDateTime.md): Return the symmetric difference of two datetime intervals — time covered by exactly one interval. - [intervalXorTime](https://northguild.dev/gmt/reference/plain/interval/intervalXorTime.md): Return the symmetric difference of two time intervals — time covered by exactly one interval. - [isAfterDate](https://northguild.dev/gmt/reference/plain/compare/isAfterDate.md): Return true if the first ISO PlainDate string represents a date after the second. - [isAfterDateTime](https://northguild.dev/gmt/reference/plain/compare/isAfterDateTime.md): Return true when `value1` is strictly after `value2` for PlainDateTime values. - [isAfterTime](https://northguild.dev/gmt/reference/plain/compare/isAfterTime.md): Return true when `value1` is strictly after `value2` for PlainTime values. - [isBeforeDate](https://northguild.dev/gmt/reference/plain/compare/isBeforeDate.md): Return true when `value1` is strictly before `value2` for PlainDate values. - [isBeforeDateTime](https://northguild.dev/gmt/reference/plain/compare/isBeforeDateTime.md): Return true when `value1` is strictly before `value2` for PlainDateTime values. - [isBeforeTime](https://northguild.dev/gmt/reference/plain/compare/isBeforeTime.md): Return true when `value1` is strictly before `value2` for PlainTime values. - [isBetweenDate](https://northguild.dev/gmt/reference/plain/compare/isBetweenDate.md): Return true when `date` is between `start` and `end` (inclusive by default). - [isBetweenDateTime](https://northguild.dev/gmt/reference/plain/compare/isBetweenDateTime.md): Return true when `dateTime` is between `start` and `end` (inclusive by default). - [isBetweenTime](https://northguild.dev/gmt/reference/plain/compare/isBetweenTime.md): Return true when `time` is between `start` and `end` (inclusive by default). - [isBusinessDay](https://northguild.dev/gmt/reference/plain/compare/isBusinessDay.md): Return true when `value` is a working day in `calendar`. - [isFuture](https://northguild.dev/gmt/reference/plain/compare/isFuture.md): Return true when `value` is strictly after today, per the system clock and system timeZone. - [isLeapYear](https://northguild.dev/gmt/reference/plain/validate/isLeapYear.md): Return true when the given PlainDate falls in a leap year. - [isPast](https://northguild.dev/gmt/reference/plain/compare/isPast.md): Return true when `value` is strictly before today, per the system clock and system timeZone. - [isRelativeDay](https://northguild.dev/gmt/reference/plain/compare/isRelativeDay.md): Return true when `value` falls `offsetDays` days from today, per the system clock and system timeZone. - [isThisUnit](https://northguild.dev/gmt/reference/plain/compare/isThisUnit.md): Return true when `value` falls in the same `unit` as today, per the system clock and system timeZone. - [isValidCalendarDate](https://northguild.dev/gmt/reference/plain/validate/isValidCalendarDate.md): Return true if `value` is a valid GMT PlainDate string: a bare ISO date ("2024-10-03") or an RFC 9557 calendar-annotated date ("2024-10-03[u-ca=hebrew]"), as `Temporal.PlainDate#toString()` and `convertDateToCalendar` write it. - [isValidDate](https://northguild.dev/gmt/reference/plain/validate/isValidDate.md): Return true if `value` is a valid ISO PlainDate string. - [isValidDateCycleField](https://northguild.dev/gmt/reference/plain/validate/isValidDateCycleField.md): Return true when `field` is a valid DateCycleField. - [isValidDateDurationUnit](https://northguild.dev/gmt/reference/plain/validate/isValidDateDurationUnit.md): Return true when `unit` is a valid DateDurationUnit. - [isValidDateInterval](https://northguild.dev/gmt/reference/plain/interval/isValidDateInterval.md): Return true if `start` and `end` form a valid date interval — both parseable as ISO PlainDate strings and `start <= end`. - [isValidDateRange](https://northguild.dev/gmt/reference/plain/validate/isValidDateRange.md): Return whether `value1` is before `value2`. - [isValidDateTime](https://northguild.dev/gmt/reference/plain/validate/isValidDateTime.md): Return true when `value` is a valid PlainDateTime string. - [isValidDateTimeCycleField](https://northguild.dev/gmt/reference/plain/validate/isValidDateTimeCycleField.md): Return true when `field` is a valid DateTimeCycleField (a valid DateCycleField or TimeCycleField). Used by `cycleDateTime` and `cycleZoned`, which can cycle either kind of field. - [isValidDateTimeDurationUnit](https://northguild.dev/gmt/reference/plain/validate/isValidDateTimeDurationUnit.md): Return true when `unit` is a valid DateTimeDurationUnit. - [isValidDateTimeInterval](https://northguild.dev/gmt/reference/plain/interval/isValidDateTimeInterval.md): Return true if `start` and `end` form a valid datetime interval — both parseable as ISO PlainDateTime strings and `start <= end`. - [isValidDateTimeRange](https://northguild.dev/gmt/reference/plain/validate/isValidDateTimeRange.md): Return true if `value1` and `value2` form a valid datetime range — both parseable as ISO PlainDateTime strings and `value1` before `value2`. - [isValidDateTimeUnit](https://northguild.dev/gmt/reference/plain/validate/isValidDateTimeUnit.md): Return true when `unit` is a valid DateTimeUnit. - [isValidDateUnit](https://northguild.dev/gmt/reference/plain/validate/isValidDateUnit.md): Return true when `unit` is a valid DateUnit. - [isValidIsoDateLike](https://northguild.dev/gmt/reference/plain/validate/isValidIsoDateLike.md): Return true when the input is a valid PlainDate or PlainDateTime ISO string. - [isValidSqlDateTime](https://northguild.dev/gmt/reference/plain/validate/isValidSqlDateTime.md): Return true when `value` is a real SQL timestamp literal without a time zone: the `YYYY-MM-DD HH:MM:SS[.fff]` value of a standard SQL `TIMESTAMP` or a MySQL/SQLite `DATETIME` column. It checks one date-and-time value, not a SQL statement. - [isValidTime](https://northguild.dev/gmt/reference/plain/validate/isValidTime.md): Return true when `value` is a valid ISO PlainTime string. - [isValidTimeCycleField](https://northguild.dev/gmt/reference/plain/validate/isValidTimeCycleField.md): Return true when `field` is a valid TimeCycleField. - [isValidTimeDurationUnit](https://northguild.dev/gmt/reference/plain/validate/isValidTimeDurationUnit.md): Return true when `unit` is a valid TimeDurationUnit. - [isValidTimeInterval](https://northguild.dev/gmt/reference/plain/interval/isValidTimeInterval.md): Return true if `start` and `end` form a valid time interval — both parseable as ISO PlainTime strings and `start <= end`. - [isValidTimeRange](https://northguild.dev/gmt/reference/plain/validate/isValidTimeRange.md): Return true if `value1` and `value2` form a valid time range — both parseable as ISO PlainTime strings and `value1` before `value2`. - [isValidTimeUnit](https://northguild.dev/gmt/reference/plain/validate/isValidTimeUnit.md): Return true when `unit` is a valid TimeUnit. - [isWeekend](https://northguild.dev/gmt/reference/plain/compare/isWeekend.md): Return true when `value` falls on a weekend day for `locale`. - [LocaleNameStyle](https://northguild.dev/gmt/reference/types/LocaleNameStyle.md): The calendar-name styles supported by GMT's locale name lookups. - [mapDatesInRange](https://northguild.dev/gmt/reference/plain/map/mapDatesInRange.md): Return an array of ISO PlainDate strings between `startDate` and `endDate` inclusive. - [mapDaysInMonth](https://northguild.dev/gmt/reference/plain/map/mapDaysInMonth.md): Return an array of ISO PlainDate strings for every day in the given year-month. - [maxDate](https://northguild.dev/gmt/reference/plain/calculate/maxDate.md): Return the latest (maximum) of the given PlainDate values. - [maxDateTime](https://northguild.dev/gmt/reference/plain/calculate/maxDateTime.md): Return the latest (maximum) of the given PlainDateTime values. - [maxTime](https://northguild.dev/gmt/reference/plain/calculate/maxTime.md): Return the latest (maximum) of the given PlainTime values. - [mergeIntervalsDate](https://northguild.dev/gmt/reference/plain/interval/mergeIntervalsDate.md): Collapse a list of date intervals into the minimum set of non-overlapping intervals. - [mergeIntervalsDateTime](https://northguild.dev/gmt/reference/plain/interval/mergeIntervalsDateTime.md): Collapse a list of datetime intervals into the minimum set of non-overlapping intervals. - [mergeIntervalsTime](https://northguild.dev/gmt/reference/plain/interval/mergeIntervalsTime.md): Collapse a list of time intervals into the minimum set of non-overlapping intervals. - [minDate](https://northguild.dev/gmt/reference/plain/calculate/minDate.md): Return the earliest (minimum) of the given PlainDate values. - [minDateTime](https://northguild.dev/gmt/reference/plain/calculate/minDateTime.md): Return the earliest (minimum) of the given PlainDateTime values. - [minTime](https://northguild.dev/gmt/reference/plain/calculate/minTime.md): Return the earliest (minimum) of the given PlainTime values. - [nextWeekday](https://northguild.dev/gmt/reference/plain/calculate/nextWeekday.md): Return a PlainDate ISO string for the next occurrence of `dayOfWeek` after `value` (or on it, with `inclusive: true`). - [parseDateTimeWithPattern](https://northguild.dev/gmt/reference/plain/parse/parseDateTimeWithPattern.md): Parse a datetime string against a caller-supplied token pattern (e.g. `"dd/MM/yyyy HH:mm:ss"`, `"dd-MMM-yyyy h:mm a"`) and return it as an ISO `PlainDateTime` string. - [parseDateWithPattern](https://northguild.dev/gmt/reference/plain/parse/parseDateWithPattern.md): Parse a date string against a caller-supplied token pattern (e.g. `"dd/MM/yyyy"`, `"dd-MMM-yyyy"`) and return it as an ISO `PlainDate` string. - [parseDayFromDate](https://northguild.dev/gmt/reference/plain/parse/parseDayFromDate.md): Return the day of month (1-31) for a given ISO 8601 date string. - [parseDayFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseDayFromDateTime.md): Return the day of month (1-31) for a given ISO 8601 datetime string. - [parseDayOfWeekFromDate](https://northguild.dev/gmt/reference/plain/parse/parseDayOfWeekFromDate.md): Return the day of week (1-7) for a given ISO 8601 date string. - [parseDayOfWeekFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseDayOfWeekFromDateTime.md): Return the day of week (1-7) for a given ISO 8601 datetime string. - [parseHourFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseHourFromDateTime.md): Return the hour (00-23) for a given ISO 8601 datetime string. - [parseHourFromTime](https://northguild.dev/gmt/reference/plain/parse/parseHourFromTime.md): Return the hour (0-23) for a given ISO 8601 time string. - [parseMicrosecondFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseMicrosecondFromDateTime.md): Return the microsecond (0-999) for a given ISO 8601 datetime string. - [parseMicrosecondFromTime](https://northguild.dev/gmt/reference/plain/parse/parseMicrosecondFromTime.md): Return the microsecond (0-999) for a given ISO 8601 time string. - [parseMillisecondFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseMillisecondFromDateTime.md): Return the millisecond (0-999) for a given ISO 8601 datetime string. - [parseMillisecondFromTime](https://northguild.dev/gmt/reference/plain/parse/parseMillisecondFromTime.md): Return the millisecond (0-999) for a given ISO 8601 time string. - [parseMinuteFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseMinuteFromDateTime.md): Return the minute (0-59) for a given ISO 8601 datetime string. - [parseMinuteFromTime](https://northguild.dev/gmt/reference/plain/parse/parseMinuteFromTime.md): Return the minute (0-59) for a given ISO 8601 time string. - [parseMonthFromDate](https://northguild.dev/gmt/reference/plain/parse/parseMonthFromDate.md): Return the month (1-12) for a given ISO 8601 date string. - [parseMonthFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseMonthFromDateTime.md): Return the month (1-12) for a given ISO 8601 datetime string. - [parseNanosecondFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseNanosecondFromDateTime.md): Return the nanosecond (0-999) for a given ISO 8601 datetime string. - [parseNanosecondFromTime](https://northguild.dev/gmt/reference/plain/parse/parseNanosecondFromTime.md): Return the nanosecond (0-999) for a given ISO 8601 time string. - [parseSecondFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseSecondFromDateTime.md): Return the second (0-59) for a given ISO 8601 datetime string. - [parseSecondFromTime](https://northguild.dev/gmt/reference/plain/parse/parseSecondFromTime.md): Return the second (0-59) for a given ISO 8601 time string. - [parseSqlDateTime](https://northguild.dev/gmt/reference/plain/parse/parseSqlDateTime.md): Parse a SQL timestamp literal without a time zone — the `YYYY-MM-DD HH:MM:SS[.fff]` form of standard SQL `TIMESTAMP` and MySQL/SQLite `DATETIME` columns — into a plain ISO 8601 datetime string. - [parseTimeWithPattern](https://northguild.dev/gmt/reference/plain/parse/parseTimeWithPattern.md): Parse a time string against a caller-supplied token pattern (e.g. `"HH:mm:ss"`, `"h:mm a"`) and return it as an ISO `PlainTime` string. - [parseUnitFromDate](https://northguild.dev/gmt/reference/plain/parse/parseUnitFromDate.md): Return a specific date unit extracted from a PlainDate string. - [parseUnitFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseUnitFromDateTime.md): Return a specific unit extracted from a PlainDateTime string. - [parseUnitFromTime](https://northguild.dev/gmt/reference/plain/parse/parseUnitFromTime.md): Return a specific time unit extracted from a PlainTime string. - [parseWeekFromDate](https://northguild.dev/gmt/reference/plain/parse/parseWeekFromDate.md): Return the week number for a given ISO 8601 date string. - [parseWeekFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseWeekFromDateTime.md): Return the week number for a given ISO 8601 datetime string. - [parseYearFromDate](https://northguild.dev/gmt/reference/plain/parse/parseYearFromDate.md): Return the year for a given ISO 8601 date string. - [parseYearFromDateTime](https://northguild.dev/gmt/reference/plain/parse/parseYearFromDateTime.md): Return the year for a given ISO 8601 datetime string. - [previousWeekday](https://northguild.dev/gmt/reference/plain/calculate/previousWeekday.md): Return a PlainDate ISO string for the previous occurrence of `dayOfWeek` before `value` (or on it, with `inclusive: true`). - [roundDate](https://northguild.dev/gmt/reference/plain/calculate/roundDate.md): Round an ISO 8601 date string to the specified date unit. - [roundDateTime](https://northguild.dev/gmt/reference/plain/calculate/roundDateTime.md): Round an ISO 8601 datetime string to the specified date-time unit. - [roundTime](https://northguild.dev/gmt/reference/plain/calculate/roundTime.md): Round an ISO 8601 time string to the specified time unit. - [setDate](https://northguild.dev/gmt/reference/plain/calculate/setDate.md): Return a PlainDate ISO string with the given `fields` set on `value`. - [setDateTime](https://northguild.dev/gmt/reference/plain/calculate/setDateTime.md): Return a PlainDateTime ISO string with the given `fields` set on `value`. - [setTime](https://northguild.dev/gmt/reference/plain/calculate/setTime.md): Return a PlainTime ISO string with the given `fields` set on `value`. - [sortDates](https://northguild.dev/gmt/reference/plain/calculate/sortDates.md): Sort an array of PlainDate values in ascending or descending order. - [sortDateTimes](https://northguild.dev/gmt/reference/plain/calculate/sortDateTimes.md): Sort an array of PlainDateTime values in ascending or descending order. - [sortTimes](https://northguild.dev/gmt/reference/plain/calculate/sortTimes.md): Sort an array of PlainTime values in ascending or descending order. - [splitIntervalByUnitDate](https://northguild.dev/gmt/reference/plain/interval/splitIntervalByUnitDate.md): Split a date interval into sub-intervals of `amount × unit`. - [splitIntervalByUnitDateTime](https://northguild.dev/gmt/reference/plain/interval/splitIntervalByUnitDateTime.md): Split a date-time interval into sub-intervals of `amount × unit`. - [splitIntervalByUnitTime](https://northguild.dev/gmt/reference/plain/interval/splitIntervalByUnitTime.md): Split a time interval into sub-intervals of `amount × unit`. - [startOfDate](https://northguild.dev/gmt/reference/plain/calculate/startOfDate.md): Return the start of the specified date `unit` for a given ISO 8601 date string. - [startOfDateTime](https://northguild.dev/gmt/reference/plain/calculate/startOfDateTime.md): Return the start of the specified date-time `unit` for a given ISO 8601 datetime string. - [startOfQuarterForDate](https://northguild.dev/gmt/reference/plain/calculate/startOfQuarterForDate.md): Return the first day of the quarter for a given ISO date. - [startOfQuarterForDateTime](https://northguild.dev/gmt/reference/plain/calculate/startOfQuarterForDateTime.md): Return the start of the quarter for a given ISO datetime. - [startOfTime](https://northguild.dev/gmt/reference/plain/calculate/startOfTime.md): Return the start of the specified time `unit` for a given ISO 8601 time string. - [subtractBusinessDays](https://northguild.dev/gmt/reference/plain/calculate/subtractBusinessDays.md): Return a PlainDate ISO string with `amount` working days subtracted from `value`. - [subtractDate](https://northguild.dev/gmt/reference/plain/calculate/subtractDate.md): Return a PlainDate ISO string with `units` subtracted from `value`. - [subtractDateTime](https://northguild.dev/gmt/reference/plain/calculate/subtractDateTime.md): Return a PlainDateTime ISO string with `units` subtracted from `value`. - [subtractTime](https://northguild.dev/gmt/reference/plain/calculate/subtractTime.md): Return a PlainTime ISO string with `units` subtracted from `value`. - [weekOfYearForDate](https://northguild.dev/gmt/reference/plain/calculate/weekOfYearForDate.md): Return the ISO week number for a given ISO 8601 date string. - [weekOfYearForDateTime](https://northguild.dev/gmt/reference/plain/calculate/weekOfYearForDateTime.md): Return the ISO week number for a given ISO 8601 datetime string. ## Reference — precision - [ArrowTimeUnit](https://northguild.dev/gmt/reference/types/ArrowTimeUnit.md): The unit of an Apache Arrow `Timestamp` column: Temporal's unit names, singular or plural, matching Arrow's `TimeUnit` (`SECOND`, `MILLISECOND`, `MICROSECOND`, `NANOSECOND`). - [ExcelDateSystem](https://northguild.dev/gmt/reference/types/ExcelDateSystem.md): Which Excel date system a serial belongs to. - [formatNanoseconds](https://northguild.dev/gmt/reference/precision/format/formatNanoseconds.md): Format nanoseconds since the Unix epoch as a decimal string, for JSON and other text transports. - [fromArrowLocalTimestamp](https://northguild.dev/gmt/reference/precision/convert/fromArrowLocalTimestamp.md): Convert the `int64` of an Apache Arrow `Timestamp` column that has no timezone to a wall-clock date-time string. - [fromArrowTimestamp](https://northguild.dev/gmt/reference/precision/convert/fromArrowTimestamp.md): Convert the `int64` of an Apache Arrow `Timestamp` column that has a timezone to a UTC instant string. - [fromDotNetTicks](https://northguild.dev/gmt/reference/precision/convert/fromDotNetTicks.md): Convert .NET `DateTime.Ticks` back to an ISO 8601 instant string. - [fromExcelSerial](https://northguild.dev/gmt/reference/precision/convert/fromExcelSerial.md): Convert an Excel day serial back to an ISO 8601 instant string. - [fromFileTime](https://northguild.dev/gmt/reference/precision/convert/fromFileTime.md): Convert a Windows `FILETIME` back to an ISO 8601 instant string. - [fromKsuid](https://northguild.dev/gmt/reference/precision/identifiers/fromKsuid.md): Read the instant a KSUID carries (segmentio/ksuid, `ksuid.go` and `base62.go`). - [fromNanoseconds](https://northguild.dev/gmt/reference/precision/convert/fromNanoseconds.md): Convert nanoseconds since the Unix epoch back to an ISO 8601 string. - [fromNtpTimestamp](https://northguild.dev/gmt/reference/precision/convert/fromNtpTimestamp.md): Convert a 64-bit NTP timestamp (RFC 5905) back to an ISO 8601 instant string. - [fromObjectId](https://northguild.dev/gmt/reference/precision/identifiers/fromObjectId.md): Read the creation second a MongoDB ObjectId carries (mongodb/specifications `bson-objectid/objectid.md`, § Specification and § Timestamp Field). - [fromParquetInt96](https://northguild.dev/gmt/reference/precision/convert/fromParquetInt96.md): Convert a Parquet `INT96` timestamp back to an ISO 8601 instant string. - [fromPgMicroseconds](https://northguild.dev/gmt/reference/precision/convert/fromPgMicroseconds.md): Convert PostgreSQL's internal `timestamptz` value back to an ISO 8601 instant string. - [fromProtoDuration](https://northguild.dev/gmt/reference/precision/convert/fromProtoDuration.md): Convert a protobuf `google.protobuf.Duration` record back to an ISO 8601 duration string. - [fromProtoTimestamp](https://northguild.dev/gmt/reference/precision/convert/fromProtoTimestamp.md): Convert a protobuf `google.protobuf.Timestamp` record back to an ISO 8601 instant string. - [fromSnowflake](https://northguild.dev/gmt/reference/precision/identifiers/fromSnowflake.md): Read the instant a Snowflake id carries, using a layout the caller supplies. - [fromUlid](https://northguild.dev/gmt/reference/precision/identifiers/fromUlid.md): Read the instant a ULID carries (ulid/spec README, § Components and § Canonical String Representation). - [fromUuidTimestamp](https://northguild.dev/gmt/reference/precision/identifiers/fromUuidTimestamp.md): Read the instant a version 1, 6 or 7 UUID carries (RFC 9562 §5.1, §5.6, §5.7). - [isValidInstant](https://northguild.dev/gmt/reference/precision/validate/isValidInstant.md): Validate whether a string is an ISO 8601 instant string the `precision/` namespace accepts. - [isValidInt64NanosecondDateTime](https://northguild.dev/gmt/reference/precision/validate/isValidInt64NanosecondDateTime.md): Validate whether a string is a plain date-time whose epoch-nanosecond count, read as if it were UTC (Arrow's rule for a zoneless timestamp), fits an `int64`: the check to run before `toArrowLocalTimestamp(dateTime, "nanosecond")`. - [isValidInt64NanosecondInstant](https://northguild.dev/gmt/reference/precision/validate/isValidInt64NanosecondInstant.md): Validate whether a string is an instant whose epoch-nanosecond count fits an `int64`: the check to run before `toArrowTimestamp(isoString, "nanosecond")`. - [isValidNanoPattern](https://northguild.dev/gmt/reference/precision/validate/isValidNanoPattern.md): Validate whether a string is a nanosecond timestamp `parseNanoseconds` will parse. - [isValidNanoseconds](https://northguild.dev/gmt/reference/precision/validate/isValidNanoseconds.md): Validate whether a value is an epoch-nanosecond `bigint` the `precision/` namespace accepts. - [ParquetInt96](https://northguild.dev/gmt/reference/types/ParquetInt96.md): A Parquet `INT96` timestamp as most readers expose it: a Julian Day Number and the nanoseconds into that day. - [parseNanoseconds](https://northguild.dev/gmt/reference/precision/parse/parseNanoseconds.md): Parse a decimal string produced by `formatNanoseconds` — typically one field of a JSON payload — back to nanoseconds since the Unix epoch. - [ProtoDuration](https://northguild.dev/gmt/reference/types/ProtoDuration.md): A protobuf `google.protobuf.Duration` as protobuf libraries expose it. - [ProtoTimestamp](https://northguild.dev/gmt/reference/types/ProtoTimestamp.md): A protobuf `google.protobuf.Timestamp` as protobuf libraries expose it. - [toArrowLocalTimestamp](https://northguild.dev/gmt/reference/precision/convert/toArrowLocalTimestamp.md): Convert an ISO 8601 plain date-time to the `int64` of an Apache Arrow `Timestamp` column that has no timezone. - [toArrowTimestamp](https://northguild.dev/gmt/reference/precision/convert/toArrowTimestamp.md): Convert an ISO 8601 instant string to the `int64` of an Apache Arrow `Timestamp` column that has a timezone. - [toDotNetTicks](https://northguild.dev/gmt/reference/precision/convert/toDotNetTicks.md): Convert an ISO 8601 instant string to .NET `DateTime.Ticks`. - [toExcelSerial](https://northguild.dev/gmt/reference/precision/convert/toExcelSerial.md): Convert an ISO 8601 instant string to an Excel day serial. - [toFileTime](https://northguild.dev/gmt/reference/precision/convert/toFileTime.md): Convert an ISO 8601 instant string to a Windows `FILETIME`. - [toNanoseconds](https://northguild.dev/gmt/reference/precision/convert/toNanoseconds.md): Convert an ISO 8601 instant string to nanoseconds since the Unix epoch. - [toNtpTimestamp](https://northguild.dev/gmt/reference/precision/convert/toNtpTimestamp.md): Convert an ISO 8601 instant string to a 64-bit NTP timestamp (RFC 5905). - [toParquetInt96](https://northguild.dev/gmt/reference/precision/convert/toParquetInt96.md): Convert an ISO 8601 instant string to a Parquet `INT96` timestamp record. - [toPgMicroseconds](https://northguild.dev/gmt/reference/precision/convert/toPgMicroseconds.md): Convert an ISO 8601 instant string to PostgreSQL's internal `timestamptz` value. - [toProtoDuration](https://northguild.dev/gmt/reference/precision/convert/toProtoDuration.md): Convert an ISO 8601 duration string to a protobuf `google.protobuf.Duration` record. - [toProtoTimestamp](https://northguild.dev/gmt/reference/precision/convert/toProtoTimestamp.md): Convert an ISO 8601 instant string to a protobuf `google.protobuf.Timestamp` record. - [truncateNanoseconds](https://northguild.dev/gmt/reference/precision/calculate/truncateNanoseconds.md): Truncate nanoseconds since the Unix epoch to the precision a store can actually hold. - [ulidTimestampPrefix](https://northguild.dev/gmt/reference/precision/identifiers/ulidTimestampPrefix.md): The first 10 characters of every ULID minted in the same millisecond as an instant, for range scans over stored ULID text (ulid/spec README, § Components and § Encoding). - [uuidV7TimestampPrefix](https://northguild.dev/gmt/reference/precision/identifiers/uuidV7TimestampPrefix.md): The first 13 characters of every version 7 UUID minted in the same millisecond as an instant, for range scans over stored UUID text (RFC 9562 §5.7, §6.11). ## Reference — regex - [calendarDate](https://northguild.dev/gmt/reference/regex/calendar-date/calendarDate.md): RegExp matching a calendar-annotated PlainDate string in the RFC 9557 form Temporal writes and reads: the ISO 8601 date, then one `[u-ca=]` calendar annotation. The digits are always ISO; the annotation only names the calendar the date is presented in (RFC 9557 §3.3). This is exactly `Temporal.PlainDate#toString()` for a non-ISO calendar. - [calendarZonedDateTime](https://northguild.dev/gmt/reference/regex/calendar-zoned-date-time/calendarZonedDateTime.md): RegExp matching a calendar-annotated ZonedDateTime string in the RFC 9557 form Temporal writes and reads — the zoned sibling of `calendarDate` (regex/calendar-date.ts): - [day](https://northguild.dev/gmt/reference/regex/date/day.md): RegExp matching an ISO 8601 day of the month: `01`–`31` (shape only; whether the day exists in its month is checked by `Temporal.PlainDate.from` in `isValidDate`). - [epcisEventTime](https://northguild.dev/gmt/reference/regex/epcis/epcisEventTime.md): RegExp matching a GS1 EPCIS 2.0 `eventTime` (and `recordTime`): the `DateTimeStamp` pattern of the EPCIS XSD (https://ref.gs1.org/standards/epcis/epcglobal-epcis-2_0.xsd, a normative artefact of EPCIS 2.0 / ISO/IEC 19987), verbatim and anchored. - [epcisTimeZoneOffset](https://northguild.dev/gmt/reference/regex/epcis/epcisTimeZoneOffset.md): RegExp matching a GS1 EPCIS 2.0 `eventTimeZoneOffset`: the `pattern` the EPCIS JSON schema (https://ref.gs1.org/standards/epcis/epcis-json-schema.json, a normative artefact of EPCIS 2.0 / ISO/IEC 19987) gives for the field, verbatim: `^([+]|[-])((0[0-9]|1[0-3]):([0-5][0-9])|14:00)$`. - [fractionalSecond](https://northguild.dev/gmt/reference/regex/time/fractionalSecond.md): RegExp matching 1–9 fractional-second digits (nanosecond precision). - [hour](https://northguild.dev/gmt/reference/regex/time/hour.md): RegExp matching an ISO 8601 hour in extended format: `00`–`23`. - [httpDate](https://northguild.dev/gmt/reference/regex/http-date/httpDate.md): RegExp matching RFC 9110 §5.6.7 IMF-fixdate — the only form GMT's `formatHttpDate` emits and the preferred HTTP-date form. Day, year, and time-of-day fields are all fixed-width per the grammar (unlike RFC 5322's leniently-sized day); the trailing "GMT" literal is mandatory, never a numeric offset. - [instantLeapSecond](https://northguild.dev/gmt/reference/regex/leap-second/instantLeapSecond.md): RegExp fragment matching an ISO 8601 leap second in every shape `Temporal.Instant.from` accepts. - [leapSecond](https://northguild.dev/gmt/reference/regex/leap-second/leapSecond.md): RegExp fragment matching an ISO 8601 leap second (second `60`) in the time of day of a date-time or time string, in every spelling Temporal's `PlainDateTime.from`/`PlainTime.from` grammar parses. - [millisecond](https://northguild.dev/gmt/reference/regex/time/millisecond.md): Backward-compatible alias for `fractionalSecond`. Prefer `fractionalSecond` for new usage — the pattern matches 1–9 digits of fractional seconds, not just milliseconds. - [minute](https://northguild.dev/gmt/reference/regex/time/minute.md): RegExp matching an ISO 8601 minute: `00`–`59`. - [month](https://northguild.dev/gmt/reference/regex/date/month.md): RegExp matching an ISO 8601 month: `01`–`12`. - [nanosecondDecimal](https://northguild.dev/gmt/reference/regex/nanoseconds/nanosecondDecimal.md): RegExp matching the canonical decimal form of a nanosecond timestamp — the shape `formatNanoseconds` emits and `parseNanoseconds` accepts. - [plainDate](https://northguild.dev/gmt/reference/regex/date/plainDate.md): RegExp matching ISO 8601 calendar date (extended): `YYYY-MM-DD` or `±YYYYYY-MM-DD`. - [plainDateTime](https://northguild.dev/gmt/reference/regex/date-time/plainDateTime.md): RegExp matching ISO 8601 local date-time (extended): `T