`dateFns`

The date-fns rendering target. Imported from rosetta-date/libraries:


import { dateFns } from 'rosetta-date/libraries'

Base grammar: ldml.
Extensions: ordinal forms, ISO week fields, the Unix epoch, and localized presets.
Support model: the reference implementation of the ldml grammar plus its own extensions; it renders the whole effective grammar, so it carries no supports set.

The extensions below are not part of the bare ldml dialect — they convert only through the dateFns library (from: momentjs, to: dateFns). A dialect → dialect conversion literalizes them instead.

Ordinals

date-fns renders ordinal forms (…o) that are not in UTS #35. They convert from the matching moment ordinals.

Meaning	Token
Quarter, ordinal	`Qo`
Month, ordinal	`Mo`
Local week of year, ordinal	`wo`
Day of month, ordinal	`do`
Day of year, ordinal	`Do`
ISO week of year, ordinal	`Io`

ISO week fields & epoch

Meaning	Token
ISO week-numbering year	`RRRR`
ISO week of year	`I`
ISO week of year, 2-digit	`II`
ISO weekday, number	`i`
Unix timestamp, seconds	`t`
Unix timestamp, milliseconds	`T`

Localized presets

date-fns spells the full preset range, including widths the moment grammar lacks (full date, time-with-zone, short date-time). See Localized presets.

Meaning	Token
Date, short / medium / long / full	`P` `PP` `PPP` `PPPP`
Time, short / with seconds / long / full	`p` `pp` `ppp` `pppp`
Date + time, short / medium / long / full	`Pp` `PPpp` `PPPppp` `PPPPpppp`

Option-gated tokens

date-fns guards a few tokens behind options you must enable in its format() call:

Day of year (D, DD) requires useAdditionalDayOfYearTokens: true.
Local week-year (YY, YYYY) requires useAdditionalWeekYearTokens: true.

rosetta-date produces the standards-correct token; enabling these options is the caller’s responsibility. The converter does not track which options you enabled — if a token needs one you did not pass, date-fns throws at format() time, which is the authoritative signal for your exact version.