Locale-aware formatting for Tempo values, dispatching to the Localize library.

Tempo.to_string/1,2 and the String.Chars implementation for Tempo, Tempo.Interval, and Tempo.IntervalSet route through this module. Callers don't need to use it directly.

Rendering rule — Tempo values are intervals

A %Tempo{} at year or month resolution is a bounded span, and its user-visible rendering reflects that span. Rule:

• ~o"2026" (year resolution) → "Jan – Dec 2026". Iteration over a year yields months; the first and last months are shown.

• ~o"2026-06" (month resolution) → "Jun 1 – 30, 2026". Iteration over a month yields days; first and last day.

• ~o"2026-06-15" (day resolution) → "Jun 15, 2026". A day is atomic at human display granularity; collapse to a single value.

• ~o"2026-06-15T14:30" (minute or finer) → "Jun 15, 2026, 2:30 PM". Same collapse rationale.

The cutoff between "expand as closed interval" and "collapse as single value" lives at day granularity by design — matching how people talk: "2026" is January-through-December; "June 2026" is June 1 to 30; "June 15" is just June 15.

Closed vs half-open at the display boundary

The underlying interval is always half-open [from, to). For display we compute the closed last member — to - 1 iteration_unit — so users see "Jan – Dec 2026", not "Jan – Jan 2026/2027". The closure happens purely at the display layer; the internal representation is unchanged.

Calendar awareness

The map passed to Localize carries the Tempo's :calendar field, so Localize selects the appropriate CLDR data when available for that calendar. Coverage of non-Gregorian calendars depends on Localize's CLDR data and may fall back to Gregorian-equivalent formatting where calendar-specific data is absent.