Unicode Frequently Asked Questions


Q: How can I find out whether a particular issue is covered by a specification published by the Consortium. And where do I look it up?

The Unicode Standard and related standards contain a number of specifications or guidelines for dealing with different programming tasks. Sometimes it's hard to find these as they are not all provided as specific, dedicated documents.

The following table lists subject areas for which the Unicode Consortium provides specifications, with a location and brief description what each specification covers. Citations of chapters or section numbers refer to the core specification of the Unicode Standard.


Character Properties: common properties such as Name, Alphabetic, Letter, White-Space, General Category, Default-Ignorable, plus those used in other specifications

Chapter 4

Character Properties for CJK Ideographs: property information specific to CJK ideographs and character properties (Unihan)

UAX #38

Unicode Character Database: general documentation about the UCD

UAX #44

UCD in XML: description of the XML representation of the UCD

UAX #42

Case Operations: conversion/detection of Upper/Lower/Titlecase, case folding, case matching. See also § 4.2 Case.

§ 3.13

Characters with Unusual Properties: characters that implementers need to pay special attention to

§ 4.12

Script Property: usage model for determining text runs in a given script

UAX #24

Use of Characters in Mathematical Contexts: guidelines for mathematical usage

UTR #25

Unicode Emoji: guidelines for the use and display of Unicode emoji characters

UTR #51

Unicode Named Character Sequences: specifies the syntax for named character sequences

UAX #34


Unicode Encoding Forms: UTF-8, UTF-16, UTF-32 conversion and validation

§ 3.9

Unicode Encoding Schemes: UTF-8, UTF-16 (BE/LE), UTF-32 (BE/LE) conversion and validation

§ 3.10

Binary Order: UTF-8 order vs. UTF-16 order

§ 5.17

Character Mapping Markup Language: mapping Unicode to and from legacy code pages

UTS #22

A Standard Compression Scheme for Unicode: how to compress Unicode to about the same size as legacy

UTS #6

UTF-EBCDIC: encapsulating Unicode on EBCDIC systems

UTR #16

Compatibility Encoding Scheme for UTF-16: 8-Bit (CESU-8): a compatibility 8-bit encoding scheme

UTR #26

Variation Sequences: standardized, emoji and ideographic variation sequences

§ 23.4

Ideographic Variation Database: repository of variation sequences for specified collections of Han glyphs

UTS #37

Comparison (Normalization, Collation)

Canonical Equivalence: when character sequences are equivalent; canonical ordering

§ 3.11

Unicode Normalization Forms: how to normalize text for comparison, also § 3.11 definitions

UAX #15

Unicode Collation Algorithm: the default mechanism for comparing, searching, matching, and ordering Unicode text

UTS #10


Hangul Syllables: boundaries, parsing, (de/)composition, names

§ 3.12

Decimal Numbers: conversion and validation

§ 5.5

Unicode Regular Expression Guidelines: the features required in supporting regular expressions with Unicode

UTS #18

Unicode Identifiers and Syntax: how to parse identifiers

UAX #31

Unicode Source Code Handling: guidance for programming language designers on handling security issues in Unicode program text


Language Information in Plain Text, also § 23.9 Tag Characters

§ 5.10

Variation Selectors: use, validation

§ 23.4

Ideographic Description Sequences: use, validation

§ 18.2


Newline Guidelines: how to handle newline characters

§ 5.8

Line Breaking Algorithm: the default way to determine where to linewrap

UAX #14

Text Segmentation: the default way to break text into grapheme clusters, words, and sentences

UAX #29


The Bidirectional Algorithm: required for display of Arabic and Hebrew text

UAX #9

Arabic Mark Rendering: sequence details for stable rendering of multiple marks

UTR #53

East Asian Width: the default determination of character width in East Asian contexts

UAX #11

Minimal shaping requirements for Arabic, Devanagari, Tamil, and other complex scripts

Chapters 9-15

Vertical orientation adjustments for characters

UTR #50

Locale Data

Locale Data Mark-up Language (LDML): used for Interchange of locale data used for internationalization

UTS #35

Common Locale Data Repository (CLDR): a repository of LDML data for hundreds of locales


Identifiers and Security

Identifier and Pattern Syntax: security issues for identifiers

UAX #31

Unicode Security Considerations: guidelines for recognizing Unicode security problems and dealing with them

UTR #36

Unicode Security Mechanisms: useful tools for detecting spoofs

UTS #39

Unicode IDNA Compatibility Processing: mapping for IDNA2008, and compatibility processing for IDNA2003

UTS #46

Q: Which Unicode specifications are normative?

Some Unicode specifications are normative and others are informative. For sections from the core specification of the Unicode Standard, the material in Chapter 3, Conformance, and most of Chapter 4, Character Properties, are normative, while material in other sections is generally informative. The Unicode Standard Annexes (UAX) are formally a part of the Unicode Standard, and most of the material in them is normative, unless otherwise indicated in the annex itself. For Unicode Technical Standards (UTS), the specifications are normative parts of those independent standards. Unicode Technical Reports (UTR) contain informative material. For more information about UAXs, UTSes, and UTRs, see About Unicode Technical Reports.