A time, datetime or local-datetime finer than a microsecond (DXN.md §1.3, Jan, 2026-10-20: dates and times carry nanoseconds). Elixir's own Time, DateTime and NaiveDateTime stop at the microsecond, so a value that needs more is held as the native value to the microsecond and the nanoseconds past it, 1 to 999. A value that fits a microsecond is the native one, as before.

iex> {:ok, t} = Dextrin.decode(~s|@time "14:30:00.123456789"|)
iex> {t.value, t.nanosecond}
{~T[14:30:00.123456], 789}