Swift FormatStyle

Format values for human-readable display using the FormatStyle protocol and Foundation's concrete format styles. Replaces legacy Formatter subclasses with a type-safe, composable, cacheable API.

Locale-aware display is an i18n concern even when the app is not adding new languages. When reviewing user-facing FormatStyle output or SwiftUI Text(_:format:), always include an actionable preview/test step for the exact rendered UI in representative locales such as en_US, de_DE, ar_SA, and ja_JP; check separators, numbering systems, calendars, currency and unit conventions, text direction, and layout-sensitive output. Keep this skill focused on FormatStyle, ParseableFormatStyle, parsing, and reusable formatter API design; route broader localization work such as String Catalogs, bundles, plurals, localized copy, and RTL layout review to ios-localization. Do not use "not adding languages" as the reason to skip ios-localization; locale-sensitive formatting can be a localization review issue without translation work.

Docs: FormatStyle

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