TR35 Conformance

This document maps the features defined in Unicode Technical Standard #35 (LDML) version 48 against the implementation status of the Localize library.

Two areas are explicitly out of scope:

Part 7 — Keyboards. Not relevant to a formatting library.
Part 8 — Person Names. Implemented as the separate localize_person_names package, which uses Localize's person-name locale data (stored under the :person_names key in each locale ETF) and implements the full TR35 Part 8 formatting algorithm.

Legend

Implemented — feature is present and tested.
Partial — core functionality exists but some sub-features are missing.
Not implemented — feature is absent.

Part 1 — Core (tr35.html)

Unicode Language and Locale Identifiers

Feature	Status	Notes
BCP 47 / RFC 5646 language tag parsing	Implemented	`Localize.Rfc5646.Parser`, pre-compiled NimbleParsec grammar.
Unicode locale extensions (`-u-`)	Implemented	Calendar (`ca`), collation (`co`), currency (`cu`), number system (`nu`), hour cycle (`hc`), first day (`fw`), region override (`rg`), measurement system (`ms`), and others.
Transformed extensions (`-t-`)	Implemented	Parser and struct support in `Localize.LanguageTag`.
Private use subtags (`-x-`)	Implemented
Grandfathered and irregular tags	Implemented
Locale ID canonicalization	Partial	Alias resolution via supplemental data. Full Annex C canonicalization algorithm not independently verified.

Locale Inheritance and Matching

Feature	Status	Notes
Parent locale chain	Implemented	`Localize.Locale.parent/1` uses CLDR parent locale data.
Likely subtags	Implemented	`Localize.LanguageTag.add_likely_subtags/1` and `remove_likely_subtags/1`.
Locale matching / best match	Implemented	`Localize.LanguageTag.best_match/3` using CLDR language matching data.
Default content locales	Not implemented
Locale inheritance for data lookup	Partial	`Locale.get/3` supports `:fallback` option to walk parent chain. Not all data accessors use it consistently.

Validity Data

Feature	Status	Notes
Language validity	Implemented	`Localize.Validity` with ETF data.
Script validity	Implemented
Territory validity	Implemented
Variant validity	Implemented
Unit validity	Implemented
Subdivision validity	Implemented
U and T extension validity	Implemented

Part 2 — General (tr35-general.html)

Display Names

Feature	Status	Notes
Language display names	Implemented	`Localize.Language.display_name/2` with `:standard`, `:short`, `:long`, `:menu`, and `:variant` styles.
Script display names	Implemented	`Localize.Script.display_name/2` with `:standard`, `:short`, `:stand_alone`, and `:variant` styles.
Territory display names	Implemented	`Localize.Territory.display_name/2` with `:standard`, `:short`, `:variant` styles.
Variant display names	Not implemented
Key/type display names	Not implemented
Locale display names	Implemented	`Localize.Locale.LocaleDisplay.display_name/2` implements the CLDR locale display name algorithm.

Layout

Feature	Status	Notes
Character order (LTR/RTL)	Not implemented
Line order	Not implemented

Character Elements

Feature	Status	Notes
Exemplar characters	Not implemented
Ellipsis patterns	Implemented	`Localize.ellipsis/2` with `:initial`, `:medial`, `:final`, `:word_initial`, `:word_medial`, `:word_final` styles.
Parse lenient characters	Not implemented

Delimiters

Feature	Status	Notes
Quotation marks	Implemented	`Localize.quote/2` with locale-appropriate primary and alternate quotation marks.

Measurement System Data

Feature	Status	Notes
Measurement system per territory	Implemented	`Localize.validate_measurement_system/1` and supplemental data.
Paper size per territory	Not implemented

Unit Elements

Feature	Status	Notes
Unit identifiers (simple, compound)	Implemented	`Localize.Unit.Parser` parses full CLDR unit identifier syntax including SI prefixes, powers, per-units.
Unit formatting with plural patterns	Implemented	`Localize.Unit.to_string/2` with `:long`, `:short`, `:narrow` styles.
Compound unit formatting	Implemented	Multiplication, division, and power patterns.
Mixed/sequence units	Partial	`Localize.Unit` struct supports mixed units; formatting coverage not fully verified.
Duration unit patterns (hms)	Implemented	`Localize.Duration.to_time_string/2` formats durations as `"hh:mm:ss"` with unbounded hours. `to_string/2` formats as localized unit list (e.g., "11 months and 30 days").
Coordinate units (N/S/E/W)	Not implemented
Unit conversion	Implemented	`Localize.Unit.Conversion` with factor/offset mappings to base units.
Unit preferences by territory	Implemented	Territory and usage-based unit selection from supplemental data.
Grammatical case in units	Partial	`:grammatical_case` option supported in formatter with `:nominative` default. Full case/gender/definiteness coverage depends on locale data.
Grammatical gender in units	Partial	Data structures present; not all locales exercised.

Transforms

Feature	Status	Notes
General character transforms	Separate library	unicode_transform implements the CLDR transform rules engine.
Script-to-script transliteration	Separate library	Provided by `unicode_transform`.
Number digit transliteration	Implemented	`Localize.Number.Transliterate` for numeric digit systems (e.g., Latin → Arabic-Indic).

List Patterns

Feature	Status	Notes
Conjunction lists ("a, b, and c")	Implemented	`Localize.List.to_string/2` with `:and`, `:and_short` styles.
Disjunction lists ("a, b, or c")	Implemented	`:or` style.
Unit lists ("3 ft, 7 in")	Implemented	`:unit`, `:unit_short`, `:unit_narrow` styles.

Context Transforms

Feature	Status	Notes
Capitalization by context	Not implemented	No context-dependent capitalization for display names.

Segmentation

Feature	Status	Notes
Grapheme cluster boundaries	Separate library	unicode_string implements Unicode text segmentation.
Word boundaries	Separate library	Provided by `unicode_string`.
Sentence boundaries	Separate library	Provided by `unicode_string`.
Line break boundaries	Separate library	Provided by `unicode_string`.

Annotations

Feature	Status	Notes
Character/emoji labels	Not implemented
Typographic names	Not implemented

POSIX Elements

Feature	Status	Notes
Yes/no strings	Not implemented
POSIX locale identifier conversion	Implemented	`Localize.Locale` handles POSIX-style identifiers (e.g., `en_US.UTF-8`).

Part 3 — Numbers (tr35-numbers.html)

Number Systems

Feature	Status	Notes
Numeric systems (digit mapping)	Implemented	`Localize.Number.System` with 97 systems loaded from ETF.
Algorithmic systems (RBNF)	Implemented	`Localize.Number.Rbnf` for Roman numerals, CJK, spellout, etc.
Number system per locale	Implemented	`:default`, `:native`, `:traditional`, `:finance` types resolved per locale.

Number Formatting

Feature	Status	Notes
Decimal format patterns	Implemented	`Localize.Number.to_string/2` with full pattern support.
Percent formatting	Implemented	`format: :percent` option.
Currency formatting	Implemented	`format: :currency` with symbol placement, spacing.
Accounting format	Implemented	`format: :accounting` for parenthesized negatives.
Compact/short formats ("1.2M")	Implemented	`format: :decimal_short`, `:decimal_long`, `:currency_short`, `:currency_long`.
Scientific notation	Implemented	Exponent formatting with configurable digits.
Significant digits	Implemented	`@` pattern character for significant digit control.
Number padding	Implemented	`*` pattern character for fixed-width padding.
Grouping separators	Implemented	Primary and secondary grouping sizes.
Rounding	Implemented	Pattern-specified increments, half-even default.
Special values (NaN, Infinity)	Implemented
Number symbols per locale	Implemented	Decimal, grouping, percent, minus, plus, exponential, etc.

Number Parsing

Feature	Status	Notes
String to number parsing	Implemented	`Localize.Number.Parser` with locale-aware digit transliteration.
Lenient parsing	Not implemented

Number Ranges

Feature	Status	Notes
Number range formatting	Implemented	`Localize.Number.to_range_string/3` using locale-specific range patterns.
Approximate number formatting	Implemented	`Localize.Number.to_approximately_string/2`, also `to_at_least_string/2` and `to_at_most_string/2`.

Rational Numbers

Feature	Status	Notes
Fraction formatting	Implemented	`Localize.Number.to_ratio_string/2`.

Currencies

Feature	Status	Notes
Currency codes and validation	Implemented	`Localize.Currency.validate_currency/1` with ISO 4217.
Currency display names (plural)	Implemented	`Localize.Currency.display_name/2`, `pluralize/3`.
Currency symbols	Implemented	Via locale data.
Currency digits/rounding	Implemented	Supplemental currency data.
Territory currency history	Implemented	`Localize.Currency.territory_currencies/1` with date ranges.
Current currency for territory	Implemented	`Localize.Currency.current_currency_for_territory/1`.

Plural Rules

Feature	Status	Notes
Cardinal plural rules	Implemented	`Localize.Number.PluralRule.Cardinal` with all CLDR operands (n, i, f, t, v, w, c, e).
Ordinal plural rules	Implemented	`Localize.Number.PluralRule.Ordinal`.
Plural ranges	Implemented	`Localize.Number.PluralRule.Range`.
Explicit 0 and 1	Partial	Standard plural categories used; explicit 0/1 override not independently verified.

Rule-Based Number Formatting (RBNF)

Feature	Status	Notes
Spellout rules	Implemented	`Localize.Number.Rbnf` with locale-specific rule sets.
Ordinal rules	Implemented
Numbering system rules	Implemented	Roman numerals, CJK, etc. via algorithmic number systems.

Part 4 — Dates (tr35-dates.html)

Calendar Elements

Feature	Status	Notes
Month names (format/standalone, wide/abbreviated/narrow)	Implemented	`Localize.Calendar.months/2`.
Day names (format/standalone, wide/abbreviated/narrow)	Implemented	`Localize.Calendar.days/2`.
Quarter names	Implemented	`Localize.Calendar.quarters/2`.
Era names	Implemented	`Localize.Calendar.eras/2`.
Day period names (AM/PM, flexible)	Implemented	`Localize.Calendar.day_periods/2`.
Cyclic name sets (Chinese/Dangi)	Not implemented
Month patterns (leap months)	Not implemented

Date/Time Formatting

Feature	Status	Notes
Date format patterns (:short/:medium/:long/:full)	Implemented	`Localize.Date.to_string/2`.
Time format patterns (:short/:medium/:long/:full)	Implemented	`Localize.Time.to_string/2`.
DateTime combined patterns	Implemented	`Localize.DateTime.to_string/2`.
All date format pattern symbols (y, M, d, E, G, etc.)	Implemented	Full symbol set in `Localize.DateTime.Formatter`.
Hour cycle (h, H, k, K)	Implemented	Including territory-based preferences.
Day periods (a, b, B)	Implemented	AM/PM and flexible day periods.
Available formats (skeletons)	Implemented	`Localize.DateTime.Format.Match` for skeleton matching.
Interval formats	Implemented	`Localize.Interval.to_string/3` for date/time/datetime intervals.
Append items (missing fields)	Not implemented

Date/Time Parsing

Feature	Status	Notes
String to date/time parsing	Not implemented

Calendar Fields

Feature	Status	Notes
Relative date/time formatting	Implemented	`Localize.DateTime.Relative` — "yesterday", "in 3 days", etc.
Calendar field display names	Partial	Data accessible via locale data; no dedicated public function for field names.

Supplemental Date Data

Feature	Status	Notes
Calendar preferences per territory	Implemented	Supplemental data loaded from ETF.
Week data (firstDay, minDays)	Implemented	`Localize.SupplementalData.weeks/0`.
Weekend data	Implemented	Via week data.
Time data (preferred hour cycle)	Implemented	Time preferences data from ETF.
Day period rules	Implemented	Day period rule sets loaded from supplemental data.

Time Zones

Feature	Status	Notes
Timezone format symbols (z, Z, O, v, V, X, x)	Implemented	`Localize.DateTime.Formatter` handles all timezone symbols.
GMT offset formatting	Implemented	`hourFormat`, `gmtFormat`, `gmtZeroFormat` patterns.
Metazone names	Not implemented	Metazone data is not loaded or used for display name resolution.
Exemplar cities	Not implemented
Timezone fallback formatting	Partial	Offset-based fallback works; metazone name fallback chain not implemented.

Semantic Skeletons

Feature	Status	Notes
Semantic skeleton support	Not implemented	Traditional skeleton matching is implemented but the newer semantic skeleton system from TR35 Section 29-32 is not.

Supported Calendars

Feature	Status	Notes
Gregorian	Implemented	Primary calendar.
Japanese	Implemented	Era data and formatting.
Chinese	Implemented	Calendar data present.
Persian	Implemented	Calendar data present.
Coptic	Implemented	Calendar data present.
Ethiopic	Implemented	Including Amete Alem variant.
Dangi (Korean)	Implemented	Calendar data present.
Buddhist	Implemented	Era (BE), month, and day data tested.
Hebrew	Implemented	Era (AM), 13-month calendar with leap year variant tested.
Islamic variants	Implemented	`:islamic`, `:islamic_civil`, `:islamic_rgsa`, `:islamic_tbla`, `:islamic_umalqura` — eras (AH) and month names (Muharram, Ramadan, etc.) tested.
ROC (Minguo)	Implemented	Era names (B.R.O.C., Minguo) tested.
Indian (Saka)	Implemented	Calendar data present and included in `known_calendars/0`.

Part 5 — Collation (tr35-collation.html)

Core Collation

Feature	Status	Notes
UCA (Unicode Collation Algorithm)	Implemented	`Localize.Collation` with DUCET-based sort key generation.
CLDR root collation	Implemented	Uses `allkeys_CLDR` data.
Multi-level comparison (L1-L4)	Implemented	Primary through quaternary levels.
Variable weighting (shifted)	Implemented	`alternate: :shifted` option.
Normalization (NFD)	Implemented	Automatic NFD when tailoring requires it.
French secondary sorting	Implemented	`backwards: :level2` / `[backwards 2]` directive.

Collation Options (BCP 47 keys)

Feature	Status	Notes
Strength (ks)	Implemented	Levels 1-4 and identical.
Alternate (ka)	Implemented	`noignore` and `shifted`.
Backwards (kb)	Implemented	Level 2 reversal.
Normalization (kk)	Implemented
Case level (kc)	Implemented
Case first (kf)	Implemented	`upper` and `lower`.
Numeric collation (kn)	Implemented	`Localize.Collation.Numeric` for number-aware sorting.
Reorder (kr)	Implemented	Script reordering with weight remapping.
Max variable (kv)	Implemented	`space`, `punct`, `symbol`, `currency`.
Hiragana quaternary (kh)	Not implemented	Deprecated in recent UCA.

Collation Tailoring

Feature	Status	Notes
Locale-specific tailoring rules	Implemented	110 locale/type pairs covering 97 languages, extracted from CLDR XML.
Relation operators (`<`, `<<`, `<<<`, `<<<<`, `=`)	Implemented
Contractions (multi-character)	Implemented
Expansions (slash notation)	Implemented	e.g., `ccs/cs` in Hungarian.
Star syntax (`<*`)	Implemented	Used for CJK and other large character sets.
Context before (`\|`)	Not implemented
`[before N]` positioning	Not implemented
`[suppressContractions]`	Implemented	Used by cu, sr, mk.
`[optimize]`	Not applicable	Advisory hint; intentionally ignored.
`[import]`	Implemented	Resolved at extraction time — imported rules are inlined into the ETF. Supports BCP47 tags (e.g., `und-u-co-search`, `de-u-co-phonebk`) and short locale tags (e.g., `hr`).
`[strength]` directive	Not implemented	Used by ja:private-kana only.

Collation Types

Feature	Status	Notes
Standard collation	Implemented	Default type for all locales.
Search collation	Implemented	Root search rules (Arabic form equivalences, Korean jamo decomposition, `[suppressContractions]`) extracted from CLDR XML. 20 locale-specific search types with resolved imports. Accessed via `type: :search` option.
Phonebook (de), Pinyin (zh), etc.	Partial	Some non-standard types extracted; not all verified.

Collation Features

Feature	Status	Notes
Alphabetic index characters	Not implemented	No UI bucketing support.
Collation type fallback chain	Partial	Falls back to standard; full 7-step chain not verified.

Part 6 — Supplemental (tr35-info.html)

Territory Data

Feature	Status	Notes
Territory containment	Implemented	`Localize.Territory.territory_containers/0`, `territory_containment/0`.
Subdivision containment	Implemented	`Localize.Territory.territory_subdivision_containment/0`.
Territory information (GDP, population)	Implemented	`Localize.Territory.info/1`.
Language population data	Implemented	Via territory info.
Emoji flags	Implemented	`Localize.Territory.unicode_flag/1`.

Supplemental Language Data

Feature	Status	Notes
Scripts per language	Not implemented	Data not exposed as a public API.
Language grouping (families)	Not implemented

Code Mappings

Feature	Status	Notes
Territory code mappings (alpha-2/3, FIPS, numeric)	Implemented	`Localize.Territory.territory_codes/0`.
Currency code mappings	Implemented	ISO 4217 via `Localize.Currency`.

Aliases

Feature	Status	Notes
Language aliases	Implemented	Supplemental alias data loaded from ETF.
Territory aliases	Implemented
Script aliases	Implemented
Variant aliases	Implemented

Parent Locales

Feature	Status	Notes
CLDR parent locale data	Implemented	`Localize.Locale.parent/1`.

Unit Data (Supplemental)

Feature	Status	Notes
Unit conversion factors	Implemented	Extracted from CLDR XML via `scripts/extract_unit_data.exs`.
Unit preferences per territory	Implemented
Unit quantities and base units	Implemented
SI and binary prefixes	Implemented	`Localize.Unit.Parser` handles all CLDR prefixes.

Coverage Levels

Feature	Status	Notes
Coverage level assessment	Not implemented

Part 9 — MessageFormat (tr35-messageFormat.html)

MF2 Syntax

Feature	Status	Notes
Simple messages	Implemented	`Localize.Message.Parser` with pre-compiled NimbleParsec grammar.
Complex messages	Implemented
Quoted patterns (`{{...}}`)	Implemented
Text and escape sequences	Implemented
Declarations (`.input`, `.local`)	Implemented	`Localize.Message.Interpreter` handles all declaration types.
Pattern selection (`.match`)	Implemented	With selector resolution and variant ranking.
Expressions (literal, variable, function)	Implemented
Options on functions	Implemented
Markup (open, close, standalone)	Implemented	Parsed and emitted in interpreter output.
Attributes	Implemented	Parsed; treated as metadata per spec.

MF2 Default Functions

Feature	Status	Notes
`:string`	Implemented
`:number`	Implemented	Delegates to `Localize.Number.to_string/2`.
`:integer`	Implemented
`:percent`	Implemented
`:currency`	Implemented
`:unit`	Implemented	Delegates to `Localize.Unit.to_string/2`.
`:date`	Implemented	Delegates to `Localize.Date.to_string/2`.
`:time`	Implemented	Delegates to `Localize.Time.to_string/2`.
`:datetime`	Implemented	Delegates to `Localize.DateTime.to_string/2`.
`:offset`	Implemented	Subtracts offset from operand for plural selection while formatting the original value. Used for patterns like "you and N other people".

Localize-specific MF2 functions (not in the spec)

Function Notes

:list Formats a list operand by delegating to Localize.List.to_string/2. Each element is itself formatted via Localize.Chars, so a list of dates, numbers, units, etc. picks up the message's locale and forwarded options. Supports a style (or type) option whose values map to CLDR list styles: "and", "and-short", "and-narrow", "or", "or-short", "or-narrow", "unit", "unit-short", "unit-narrow". Default is "and".

Function	Notes
`:list`	Formats a list operand by delegating to `Localize.List.to_string/2`. Each element is itself formatted via `Localize.Chars`, so a list of dates, numbers, units, etc. picks up the message's locale and forwarded options. Supports a `style` (or `type`) option whose values map to CLDR list styles: `"and"`, `"and-short"`, `"and-narrow"`, `"or"`, `"or-short"`, `"or-narrow"`, `"unit"`, `"unit-short"`, `"unit-narrow"`. Default is `"and"`.

MF2 Error Handling

Feature	Status	Notes
Syntax errors	Implemented	Parser returns `{:error, reason}`.
Resolution errors (unknown function, unresolved variable)	Partial	Unknown functions fall back to string conversion rather than error.
Data model errors	Partial	Duplicate declarations and options not explicitly validated.

MF2 Data Model

Feature	Status	Notes
JSON interchange format	Implemented	`Localize.Message.JSON.to_json/2` and `from_json/1` for round-trip serialization to the TR35 §8 data model.
Bidirectional text handling	Implemented	`:bidi` option (`:none`, `:isolate`, `:auto`) wraps placeholder output in Unicode isolate characters (FSI/PDI). Supports `u:dir` attribute for per-expression overrides.

Summary

Implemented (core functionality present and tested)

Language tag parsing and validation (BCP 47 / RFC 5646)
Locale management (get/put/default/with_locale)
Likely subtags and locale matching
Number formatting (decimal, percent, currency, accounting, compact, scientific, RBNF)
Number parsing
Date, time, and datetime formatting
Interval formatting
Relative date/time formatting
Unit formatting, conversion, and preferences (also include basic math functions)
List formatting
Currency data and validation
Territory data and display names
Language display names
Locale display names
Plural rules (cardinal, ordinal, ranges)
Collation with locale tailoring (97 languages)
MessageFormat 2 parsing and interpretation
Quotation marks and ellipsis formatting

Separate libraries

General character transforms/transliteration — unicode_transform
Text segmentation (grapheme/word/sentence/line) — unicode_string

Not implemented

Date/time parsing (string to date)
Metazone display names
Semantic skeletons
Context-dependent capitalization
Collation alphabetic index (UI bucketing)
Coordinate unit formatting (N/S/E/W)
Layout direction data
Coverage level assessment
Cyclic name sets (Chinese/Dangi calendars)
Append items (missing date/time fields)

Not in scope for Localize

Emoji/character annotations and labels
Keyboards

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