[Unicode]   Technical Reports

Proposed Update

Unicode Standard Annex #44

Unicode Character Database

Version Unicode 6.0.0 draft 15
Authors Editors Mark Davis (markdavis@google.com) and Ken Whistler (ken@unicode.org)
Date 2010-09-15
This Version http://www.unicode.org/reports/tr44/tr44-5.html
Previous Version http://www.unicode.org/reports/tr44/tr44-4.html
Latest Version http://www.unicode.org/reports/tr44/
Latest Proposed Update http://www.unicode.org/reports/tr44/proposed.html
Revision 5


This annex provides the core documentation for the Unicode Character Database (UCD). It describes the layout and organization of the Unicode Character Database and how it specifies the formal definitions of the Unicode Character Properties.


This is a draft document which may be updated, replaced, or superseded by other documents at any time. Publication does not imply endorsement by the Unicode Consortium. This is not a stable document; it is inappropriate to cite this document as other than a work in progress.

A Unicode Standard Annex (UAX) forms an integral part of the Unicode Standard, but is published online as a separate document. The Unicode Standard may require conformance to normative content in a Unicode Standard Annex, if so specified in the Conformance chapter of that version of the Unicode Standard. The version number of a UAX document corresponds to the version of the Unicode Standard of which it forms a part.

Please submit corrigenda and other comments with the online reporting form [Feedback]. Related information that is useful in understanding this annex is found in Unicode Standard Annex #41, “Common References for Unicode Standard Annexes.” For the latest version of the Unicode Standard, see [Unicode]. For a list of current Unicode Technical Reports, see [Reports]. For more information about versions of the Unicode Standard, see [Versions]. For any errata which may apply to this annex, see [Errata].



Note: the information in this annex is not intended as an exhaustive description of the use and interpretation of Unicode character properties and behavior. It must be used in conjunction with the data in the other files in the Unicode Character Database, and relies on the notation and definitions supplied in The Unicode Standard. All chapter references are to Version 5.2.0 6.0.0 of the standard unless otherwise indicated.

1 Introduction

The Unicode Standard is far more than a simple encoding of characters. The standard also associates a rich set of semantics with each encoded character—properties that are required for interoperability and correct behavior in implementations, as well as for Unicode conformance. These semantics are cataloged in the Unicode Character Database (UCD), a collection of data files which contain the Unicode character code points and character names. The data files define the Unicode character properties and mappings between Unicode characters (such as case mappings).

This annex describes the UCD and provides a guide to the various documentation files associated with it. Additional information about character properties and their use is contained in the Unicode Standard and its annexes. In particular, implementers should familiarize themselves with the formal definitions and conformance requirements for properties detailed in Section 3.5, Properties in [Unicode] and with the material in Chapter 4, Character Properties in [Unicode].

The latest version of the UCD is always located on the Unicode Web site at:


The specific files for the UCD associated with this version of the Unicode Standard (6.0.0) are located at:


Stable, archived versions of the UCD associated with all earlier versions of the Unicode Standard can be accessed from:


For a description of the changes in the UCD for this version and earlier versions, see the UCD Change History.

2 Conformance

The Unicode Character Database is an integral part of the Unicode Standard.

The UCD contains normative property and mapping information required for implementation of various Unicode algorithms such as the Unicode Bidirectional Algorithm, Unicode Normalization, and Unicode Casefolding. The data files also contain additional informative and provisional character property information.

Each specification of a Unicode algorithm, whether specified in the text of [Unicode] or in one of the Unicode Standard Annexes, designates which data file(s) in the UCD are needed to provide normative property information required by that algorithm.

For information on the meaning and application of the terms, normative, informative, and provisional, see Section 3.5, Properties in [Unicode].

For information about the applicable terms of use for the UCD, see the Unicode Terms of Use.

2.1 Simple and Derived Properties

Some character properties in the UCD are simple properties. This status has no bearing on whether or not the properties are normative, but merely indicates that their values are not derived from some combination of other properties.

Other character properties are derived. This means that their values are derived by rule from some other combination of properties. Generally such rules are stated as set operations, and may or may not include explicit exception lists for individual characters.

Certain simple properties are defined merely to make the statement of the rule defining a derived property more compact or general. Such properties are known as contributory properties. Sometimes these contributory properties are defined to encapsulate the messiness inherent in exception lists. At other times, a contributory property may be defined to help stabilize the definition of an important derived property which is subject to stability guarantees.

Derived character properties are not considered second-class citizens among Unicode character properties. They are defined to make implementation of important algorithms easier to state. Included among the first-class derived properties important for such implementations are: Uppercase, Lowercase, XID_Start, XID_Continue, Math, and Default_Ignorable_Code_Point, all defined in DerivedCoreProperties.txt, as well as derived properties for the optimization of normalization, defined in DerivedNormalizationProps.txt.

Implementations should simply use the derived properties, and should not try to rederive them from lists of simple properties and collections of rules, because of the chances for error and divergence when doing so.

Definitions of property derivations are provided for information only, typically in comment fields in the data files. Such definitions may be refactored, refined, or corrected over time.

If there are any cases of mismatches between the definition of a derived property as listed in DerivedCoreProperties.txt or similar data files in the UCD, and the definition of a derived property as a set definition rule, the explicit listing in the data file should always be taken as the normative definition of the property. As described in Stability of Releases the property listing in the data files for any given version of the standard will never change for that version.

2.2 Use of Default Values

Unicode character properties have default values. Default values are the value or values that a character property takes for an unassigned code point, or in some instances, for designated subranges of code points, whether assigned or unassigned. For example, the default value of a binary Unicode character property is always "N".

For the formal discussion of default values, see D26 in Section 3.5, Properties in [Unicode]. For conventions related to default values in various data files of the UCD and for documentation regarding the particular default values of individual Unicode character properties, see Default Values.

2.3 Stability of Releases

Just as for the Unicode Standard as a whole, each version of the UCD, once published, is absolutely stable and will never change. Each released version is archived in a directory on the Unicode Web site, with a directory number associated with that version. URLs pointing to that version's directory are also stable and will be maintained in perpetuity.

Any errors discovered for a released version of the UCD are noted in [Errata], and if appropriate will be corrected in a subsequent version of the UCD.

Stability guarantees constraining how Unicode character properties can (or cannot) change between releases of the UCD are documented in the Unicode Consortium Stability Policies [Stability].

2.3.1 Changes to Properties Between Releases

Updates to character properties in the Unicode Character Database may be required for any of three reasons:

  1. To cover new characters added to the standard
  2. To add new character properties to the standard
  3. To change the assigned values for a property for some characters already in the standard

While the Unicode Consortium endeavors to keep the values of all character properties as stable as possible between versions, occasionally circumstances may arise which require changing them. In particular, as less well-documented scripts, such as those for minority languages, or historic scripts are added to the standard, the exact character properties and behavior may not fully be known when the script is first encoded. The properties for some of these characters may change as further information becomes available or as implementations turn up problems in the initial property assignments. As far as possible, any readjustment of property values based on growing implementation experience is made to be compatible with established practice.

Occasionally, a character property value is changed to prevent incorrect generalizations about a character's use based on its nominal property values. For example, U+200B ZERO WIDTH SPACE was originally classified as a space character (General_Category=Zs), but it was reclassified as a Format character (General_Category=Cf) to clearly distinguish it from space characters in its function as a format control for line breaking.

There is no guarantee that a particular value for an enumerated property will actually have characters associated with it. Also, because of changes in property value assignments between versions of the standard, a property value that once had characters associated with it may later have none. Such conditions and changes are rare, but implementations must not assume that all property values are associated with non-null sets of characters. For example, currently the special Script property value Katakana_Or_Hiragana has no characters associated with it.

2.3.2 Obsolete Properties

In some instances an entire property may become obsolete. For example, the ISO_Comment property was once used to keep track of annotations for characters used in the production of name lists for ISO/IEC 10646 code charts. As of Unicode 5.2.0 that property became obsolete, and its value is now defaulted to the null string for all Unicode code points.

An obsolete property is never removed from the UCD.

2.3.3 Deprecated Properties

Occasionally an obsolete property may also be formally deprecated. This is an indication that the property is no longer recommended for use, perhaps because its original intent has been replaced by another property or because its specification was somehow defective. For example, the Grapheme_Link property is deprecated. See also the general discussion of Deprecation.

A deprecated property is never removed from the UCD.

Table 1 lists the properties that are formally deprecated as of this version of the Unicode Standard.

Table 1. Deprecated Properties

Property Name Deprecation Version Reason
Grapheme_Link 5.0.0 Duplication of ccc=9
Hyphen 6.0.0 Supplanted by Line_Break property values
ISO_Comment 6.0.0 No longer needed for chart generation; otherwise not useful
Expands_On_NFC 6.0.0 Less useful than UTF-specific calculations
Expands_On_NFD 6.0.0 Less useful than UTF-specific calculations
Expands_On_NFKC 6.0.0 Less useful than UTF-specific calculations
Expands_On_NFKD 6.0.0 Less useful than UTF-specific calculations
FC_NFKC_Closure 6.0.0 Supplanted in usage by NFKC_Casefold; otherwise not useful

2.3.3 Stabilized Properties

Another possibility is that an obsolete property may be declared to be stabilized. Such a determination does not indicate that the property should or should not be used; instead it is a declaration that the UTC will no longer actively maintain the property or extend it for newly encoded characters. The property values of a stabilized property are frozen as of a particular release of the standard. For example, the Hyphen property was stabilized as of Version 4.0.0.

A stabilized property is never removed from the UCD.

Table 2 lists the properties that are formally stabilized as of this version of the Unicode Standard.

Table 2. Stabilized Properties

Property Name Stabilization Version
Hyphen 4.0.0
ISO_Comment 6.0.0

3 Documentation

This annex provides the core documentation for the UCD, but additional information about character properties is available in other parts of the standard and in additional documentation files contained within the UCD.

3.1 Character Properties in the Standard

The formal definitions related to character properties used by the Unicode Standard are documented in Section 3.5, Properties in [Unicode]. Understanding those definitions and related terminology is essential to the appropriate use of Unicode character properties.

See Section 4.1, Unicode Character Database, in [Unicode] for a general discussion of the UCD and its use in defining properties. The rest of Chapter 4 provides important explanations regarding the meaning and use of various normative character properties.

3.2 The Character Property Model

For a general discussion of the property model which underlies the definitions associated with the UCD, see Unicode Technical Report #23, "The Unicode Character Property Model" [UTR23]. That technical report is informative, but over the years various content from it has been incorporated into normative portions of the Unicode Standard, particularly for the definitions in Chapter 3.

UTR #23 also discusses string functions and their relation to character properties.

3.3 NamesList.html

NamesList.html formally describes the format of the NamesList.txt data file in BNF. That data file is used to drive the printing of the Unicode code charts and names list. See also Section 17.1, Character Names List, in [Unicode] for a detailed discussion of the conventions used in the Unicode names list as formatted for printing.

3.4 StandardizedVariants.html

StandardizedVariants.html documents standardized variants, showing a representative glyph for each. It is closely tied to the data file, StandardizedVariants.txt, which defines those sequences normatively.

3.5 Unihan and UAX #38

Unicode Standard Annex #38, "Unicode Han Database (Unihan)" [UAX38] describes the format and content of the Unihan Database, which collects together all property information for CJK Unified Ideographs. That annex also specifies in detail which of the Unihan character properties are normative, informative, or provisional.

The Unihan Database contains extensive and detailed mapping information for CJK Unified Ideographs encoded in the Unicode Standard, but it is aimed only at those ideographs, not at other characters used in the East Asian context in general. In contrast, East Asian legacy character sets, including important commercial and national character set standards, contain many non-CJK characters. As a result, the Unihan Database must be supplemented from other sources to establish mapping tables for those character sets.

The majority of the content of the Unihan Database is released for each version of the Unicode Standard as a collection of Unihan data files in the UCD. Because of their large size, these data files are released only as a zipped file, Unihan.zip. The details of the particular data files in Unihan.zip and the CJK properties each one contains are provided in [UAX38]. For versions of the UCD prior to Version 5.2.0, all of the CJK properties were listed together in a very large, single file, Unihan.txt.

3.6 Data File Comments

In addition to the specific documentation files for the UCD, individual data files often contain extensive header comments describing their content and any special conventions used in the data.

In some instances, individual property definition sections also contain comments with information about how the property may be derived. Such comments are informative; while they are intended to convey the intent of the derivation, in case of any mismatch between a statement of a derivation in a comment field and the actual listing of the derived property, it is the list which is to be taken as normative. See Simple and Derived Properties.

3.7 Obsolete Documentation Files

UCD.html was formerly the primary documentation file for the UCD. As of Version 5.2.0, its content has been wholly incorporated into this document.

Unihan.html was formerly the primary documentation file for the Unihan Database. As of Version 5.1.0, its content has been wholly incorporated into [UAX38].

Versions of the Unicode Standard prior to Version 4.0.0 contained small, focussed documentation files, UnicodeCharacterDatabase.html, PropList.html, and DerivedProperties.html, which were later consolidated into UCD.html.

4 UCD Files

The heart of the UCD consists of the data files themselves. This section describes the directory structure for the UCD, the format conventions for the data files, and provides documentation for data files not documented elsewhere in this annex.

4.1 Directory Structure

Each version of the UCD is released in a separate, numbered directory under the Public directory on the Unicode Web site. The content of that directory is complete for that release. It is also stable—once released, it will be archived permanently in that directory, unchanged, at a stable URL.

The specific files for the UCD associated with this version of the Unicode Standard (6.0.0) are located at:


4.1.1 UCD Files Proper

The UCD proper is located in the ucd subdirectory of the numbered version directory. That directory contains all of the documentation files and most of the data files for the UCD, including some data files for derived properties.

Although all UCD data files are version-specific for a release and most contain internal date and version stamps, the file names of the released data files do not differ from version to version. When linking to a version-specific data file, the version will be indicated by the version number of the directory for the release.

All files for derived extracted properties are in the extracted subdirectory of the ucd subdirectory. See Derived Extracted Properties for documentation regarding those data files and their content.

A number of auxiliary properties are specified in files in the auxiliary subdirectory of the ucd subdirectory. In Version 6.0.0 it contains data files specifying properties associated with Unicode Standard Annex #29, "Unicode Text Segmentation" [UAX29] and with Unicode Standard Annex #14, "Unicode Line Breaking Algorithm" [UAX14], as well as test data for those algorithms. See Segmentation Test Files and Documentation for more information about the test data.

4.1.2 UCD XML Files

The XML version of the UCD is located in the ucdxml subdirectory of the numbered version directory. See the UCD in XML for more details.

4.1.3 Charts

The code charts specific to a version of Unicode are archived as a single large pdf file in the charts subdirectory of the numbered version directory. See the readme.txt in that subdirectory and the general web page explaining the Unicode Code Charts for more details.

4.1.4 Beta Review Considerations

Prior to the formal release for any particular version of the UCD, a beta review is conducted. The beta review files are located in the same directory that is later used for the released UCD, but during the beta review period, the subdirectory structure differs somewhat and may contain temporary files, including documentation of diffs between deltas for the beta review. Also, during the beta review, all data file names are suffixed with version numbers and delta numbers. So a typical file name during beta review may be "PropList-5.2.0d13.txt" instead of the finally released "PropList.txt".

Notices contained in a ReadMe.txt file in the UCD directory during the beta review period also make it clear that that directory contains preliminary material under review, rather than a final, stable release.

4.1.5 File Directory Differences for Early Releases

The UCD in XML was introduced in Version 5.1.0, so UCD directories prior to that do not contain the ucdxml subdirectory.

UCD directories prior to Version 4.1.0 do not contain the auxiliary subdirectory.

UCD directories prior to Version 3.2.0 do not contain the extracted subdirectory.

The general structure of the file directory for a released version of the UCD described above applies to Versions 4.1.0 and later. Prior to Version 4.1.0, versions of the UCD were not self-contained, complete sets of data files for that version, but instead only contained any new data files or any data files which had changed since the prior release.

Because of this, the property files for a given version prior to Version 4.1.0 can be spread over several directories. Consult the component listings at Enumerated Versions to find out which files in which directories comprise a complete set of data files for that version.

The directory naming conventions and the file naming conventions also differed prior to Version 4.1.0. So, for example, Version 4.0.0 of the UCD is contained in a directory named 4.0-Update, and Version 4.0.1 of the UCD in a directory named 4.0-Update1. Furthermore, for these earlier versions, the data file names do contain explicit version numbers.

4.2 File Format Conventions

Files in the UCD use the format conventions described in this section, unless otherwise specified.

4.2.1 Data Fields

4.2.2 Code Points and Sequences

4.2.3 Code Point Ranges


4.2.5 Code Point Labels

Table 3. Code Point Label Tags

Tag General_Category Note
reserved Cn Noncharacter_Code_Point=F
noncharacter Cn Noncharacter_Code_Point=T
control Cc  
private-use Co  
surrogate Cs  

4.2.6 Multiple Values

4.2.7 Binary Property Values

4.2.8 Default Values

Default values for common catalog, enumeration, and numeric properties are listed in Table 4.

Table 4. Default Values for Properties

Property Name Default Value
Age unassigned
Bidi_Class L, AL, R
Block No_Block
Canonical_Combining_Class Not_Reordered (= 0)
Decomposition_Type None
East_Asian_Width Neutral (= N), Wide (= W)
General_Category Cn
Numeric_Type None
Numeric_Value NaN
Script Unknown (= Zzzz)

Default values for the Unicode character property Bidi_Class are complex. See Unicode Standard Annex #9, "The Unicode Bidirectional Algorithm" [UAX9] and DerivedBidiClass.txt for more details.

Default values for the East_Asian_Width property are also complex. This property defaults to Neutral for most code points, but defaults to Wide for unassigned code points in blocks associated with CJK ideographs. See Unicode Standard Annex #11, "East Asian Width" [UAX11] and DerivedEastAsianWidth.txt for more details.

4.2.9 Text Encoding

4.2.10 Line Termination

4.2.11 Other Conventions

4.2.12 Other File Formats

4.3 File List

The exact list of files associated with any particular version of the UCD is available on the Unicode Web site by referring to the component listings at Enumerated Versions.

The majority of the data files in the UCD provide specifications of character properties for Unicode characters. Those files and their contents are documented in detail in the Property Table section below.

The data files in the extracted subdirectory constitute reformatted listings of single character properties extracted from UnicodeData.txt or other primary data files. The reformatting is provided to make it easier to see the particular set of characters having certain values for enumerated properties, or to separate the statement of that property from other properties defined together in UnicodeData.txt. These extracted, derived data files are further documented in the Derived Extracted Properties section below.

The UCD also contains a number of test data files, whose purpose is to provide standard test cases useful in verifying the implementation of complex Unicode algorithms. See the Test Files section below for more documentation.

The remaining files in the Unicode Character Database do not directly specify Unicode properties. The important ones and their functions are listed in Table 5. The Status column indicates whether the file (and its content) is considered Normative, Informative, or Provisional.

Table 5. Files in the UCD

File Name Reference Status Description
CJKRadicals.txt [UAX38] I List of Unified CJK Ideographs and CJK Radicals that correspond to specific radical numbers used in the CJK radical stroke counts.
EmojiSources.txt Chapter 15 N Specifies source mappings to SJIS values for emoji symbols in the original implementations of these symbols by Japanese telecommunications companies.
Index.txt Chapter 17 I Index to Unicode characters, as printed in the Unicode Standard.
NamesList.txt Chapter 17 I Names list used for production of the code charts, derived from UnicodeData.txt. It contains additional annotations.
NamesList.html Chapter 17 I Documents the format of NamesList.txt.
ScriptExtensions.txt UAX #24 P Contains data about characters that are used in multiple scripts.
StandardizedVariants.txt Chapter 16 N Lists all the standardized variant sequences that have been defined, plus a textual description of their desired appearance.
StandardizedVariants.html Chapter 16 N A derived documentation file, generated from StandardizedVariants.txt, plus a list of sample glyphs showing the desired appearance of each standardized variant.
NamedSequences.txt [UAX34] N Lists the names for all approved named sequences.
NamedSequencesProv.txt [UAX34] P Lists the names for all provisional named sequences.

For more information about these files and their use, see the referenced annexes or chapters of Unicode Standard.

4.4 Zipped Files

Starting with Version 4.1.0, zipped versions of all of the UCD files, both data files and documentation files, are available under the Public/zipped directory on the Unicode Web site. Each collection of zipped files is located there in a numbered subdirectory corresponding to that version of the UCD.

Two different zipped files are provided for each version:

This bifurcation allows for better management of downloading version-specific information, because Unihan.zip contains all the pertinent CJK-related property information, while UCD.zip contains all of the rest of the UCD property information, for those who may not need the voluminous CJK data.

In versions of the UCD prior to Version 4.1.0, zipped copies of the Unihan data files (which for those versions were released as a single large text file, Unihan.txt) are provided in the same directory as the UCD data files. These zipped files are only posted for versions of the UCD in which Unihan.txt was updated.

4.5 UCD in XML

Starting with Version 5.1.0, a set of XML data files are also released with each version of the UCD. Those data files make it possible to import and process the UCD property data using standard XML parsing tools, instead of the specialized parsing required for the various individual data files of the UCD.

4.5.1 UAX #42

Unicode Standard Annex #42, "Unicode Character Database in XML" [UAX42] defines an XML schema which is used to incorporate all of the Unicode character property information into the XML version of the UCD. See that annex for details of the schema and conventions regarding the grouping of property values for more compact representations.

4.5.2 XML File List

The XML version of the UCD is contained in the ucdxml subdirectory of the UCD. The files are all zipped. The list of files is shown in Table 6.

Table 6. XML File List

File Name CJK non-CJK
ucd.all.flat.zip x x
ucd.all.grouped.zip x x
ucd.nounihan.flat.zip   x
ucd.nounihan.grouped.zip   x
ucd.unihan.flat.zip x  
ucd.unihan.grouped.zip x  

The "flat" file versions simply list all attributes with no particular compression. The "grouped" file versions apply the grouping mechanism described in [UAX42] to cut down on the size of the data files.

5 Properties

This section documents the Unicode character properties, relating them in detail to the particular UCD data files in which they are specified. For enumerated properties in particular, this section also documents the actual values which those properties can have.

An index of all the non-CJK character properties by name can be found below in the Property Summary section.

5.1 Property Summary Index

Table 7 provides a summary list of the Unicode character properties, excluding most of those specific to the Unihan data files. For a comparable index of CJK character properties, see Unicode Standard Annex #38, "Unicode Han Database (Unihan)" [UAX38].

The properties are roughly organized into groups based on their usage. This grouping is primarily for documentation convenience and except for contributory properties, has no normative implications. The link on each property leads to its description in the Table 9, Property Table above.

Table 7. Property Summary Table Index by Scope of Use

General Normalization CJK
Name Canonical_Combining_Class Ideographic
Name_Alias Decomposition_Mapping Unified_Ideograph
Block Composition_Exclusion Radical
Age Full_Composition_Exclusion IDS_Binary_Operator
General_Category Decomposition_Type IDS_Trinary_Operator
Script FC_NFKC_Closure (deprecated) Unicode_Radical_Stroke
White_Space NFC_Quick_Check Miscellaneous
Alphabetic NFKC_Quick_Check Math
Hangul_Syllable_Type NFD_Quick_Check Quotation_Mark
Noncharacter_Code_Point NFKD_Quick_Check Dash
Default_Ignorable_Code_Point Expands_On_NFC (deprecated) Hyphen (deprecated, stabilized)
Deprecated Expands_On_NFD (deprecated) STerm
Logical_Order_Exception Expands_On_NFKC (deprecated) Terminal_Punctuation
Variation_Selector Expands_On_NFKD (deprecated) Diacritic
  NFKC_Casefold Extender
  Changes_When_NFKC_Casefolded Grapheme_Base
Case Shaping and Rendering Grapheme_Extend
Uppercase Join_Control Grapheme_Link (deprecated)
Lowercase Joining_Group Unicode_1_Name
Lowercase_Mapping Joining_Type ISO_Comment (obsoletedeprecated, stabilized)
Titlecase_Mapping Line_Break Indic_Matra_Category
Uppercase_Mapping Grapheme_Cluster_Break Indic_Syllabic_Category
Case_Folding Sentence_Break Contributory Properties
Simple_Lowercase_Mapping Word_Break Other_Alphabetic
Simple_Titlecase_Mapping East_Asian_Width Other_Default_Ignorable_Code_Point
Simple_Uppercase_Mapping Bidirectional Other_Grapheme_Extend
Simple_Case_Folding Bidi_Class Other_ID_Start
Soft_Dotted Bidi_Control Other_ID_Continue
Cased Bidi_Mirrored Other_Lowercase
Case_Ignorable Bidi_Mirroring_Glyph Other_Math
Changes_When_Lowercased Identifiers Other_Uppercase
Changes_When_Uppercased ID_Continue Jamo_Short_Name
Changes_When_Titlecased ID_Start Numeric
Changes_When_Casefolded XID_Continue Numeric_Value
Changes_When_Casemapped XID_Start Numeric_Type
  Pattern_Syntax Hex_Digit
  Pattern_White_Space ASCII_Hex_Digit


5.2 About the Property Table

Table 9, Property Table The big property table below, Table 8, specifies the list of character properties defined in the UCD. Table 8 That table is divided into separate sections for each data file in the UCD. Data files which define a single property or a small number of properties are listed first, followed by the data files which define a large number of properties: DerivedCoreProperties.txt, DerivedNormalizationProps.txt, PropList.txt, and UnicodeData.txt. In some instances for these files defining many properties, the entries in the property table are grouped by type, for clarity in presentation, rather than being listed alphabetically.

In Table 9, Property Table each property is described as follows:

First Column. This column contains the name of each of the character properties specified in the respective data file. Any special status for a property, such as whether it is obsolete, deprecated, or stabilized, is also indicated in the first column.

Second Column. This column indicates the type of the property, according to the key in Table 8.

Table 8. Property Type Key

Property Type Symbol Examples
Catalog C Age, Block
Enumeration E Joining_Type, Line_Break
Binary B Uppercase, White_Space
String S Uppercase_Mapping, Case_Folding
Numeric N Numeric_Value
Miscellaneous M Name, Jamo_Short_Name

Third Column. This column indicates the status of the property: Normative or Informative or Contributory.

Fourth Column. This column provides a description of the property or properties. This includes information on derivation for derived properties, as well as references to locations in the standard where the property is defined or discussed in detail.

In the section of the table for UnicodeData.txt, the data field numbers are also supplied in parentheses at the start of the description.

For a few entries in the property table, values specified in the fields in a data file only contribute to a full definition of a Unicode character property. For example, the values in field 1 (Name) in UnicodeData.txt do not provide all the values for the Name property for all code points; Jamo.txt must also be used, and the Name property for CJK Unified Ideographs is derived by rule.

None of the Unicode character properties should be used simply on the basis of the descriptions in the property table without consulting the relevant discussions in the Unicode Standard. Because of the enormous variety of characters in the repertoire of the Unicode Standard, character properties tend not to be self-evident in application, even when the names of the properties may seem familiar from their usage with much smaller legacy character encodings.

5.3 Property Definitions

This section contains the table which describes each character property and defines its status, organized by data file in the UCD.

Table 9. Property Table

E N Basic Arabic and Syriac character shaping properties, such as initial, medial and final shapes. See Section 8.2, Arabic in [Unicode].
Bidi_Mirroring_Glyph S I Informative mapping for substituting characters in an implementation of bidirectional mirroring. This maps a subset of characters with the Bidi_Mirrored property to other characters that normally are displayed with the corresponding mirrored glyph. When a character with the Bidi_Mirrored property has the default value for Bidi_Mirroring_Glyph, that means that no other character exists whose glyph is appropriate for character-based glyph mirroring. Implementations must then use other mechanisms to implement mirroring of those characters for the Unicode Bidirectional Algorithm. See Unicode Standard Annex #9:" The Unicode Bidirectional Algorithm" [UAX9]. Do not confuse this property with the Bidi_Mirrored property itself.
Block C N List of block names, which are arbitrary names for ranges of code points. See Chapter 17 the code charts in [Unicode].
Composition_Exclusion B N Properties for A property used in normalization. See Unicode Standard Annex #15: "Unicode Normalization Forms" [UAX15]. Unlike other files, CompositionExclusions.txt simply lists the relevant code points.
S N Mapping from characters to their case-folded forms. This is an informative file containing normative derived properties.

Derived from UnicodeData and SpecialCasing.

Note: The case foldings are omitted in the data file if they are the same as the code point itself.

Age C N/I This file shows when various code points were designated/assigned in successive versions of the Unicode Standard.

The Age property is normative in the sense that it is completely specified based on when a character is encoded in the standard. However, DerivedAge.txt is provided for information. The value of the Age property for a code point can be derived by analysis of successive versions of the UCD, and Age is not used normatively in the specification of any Unicode algorithm.

Note: When using the Age property in regular expressions, an expression such as "\p{age=3.0}" matches all of the code points assigned in Version 3.0—that is, all the code points with a value less than or equal to 3.0 for the Age property. For more information, see Unicode Technical Standard #18, "Unicode Regular Expressions" [UTS18].

East_Asian_Width E I Properties for determining the choice of wide versus narrow glyphs in East Asian contexts. Property values are described in Unicode Standard Annex #11, "East Asian Width" [UAX11].
Hangul_Syllable_Type E N The values L, V, T, LV, and LVT used in Chapter 3, Conformance in [Unicode].
Indic_Matra_Category E P A provisional property defining the placement categories for dependent vowels in Indic scripts.
Indic_Syllabic_Category E P A provisional property defining the structural categories of syllabic components in Indic scripts.
Jamo_Short_Name M C The Hangul Syllable names are derived from the Jamo Short Names, as described in Chapter 3, Conformance in [Unicode].
Line_Break E N Properties for line breaking. For more information, see Unicode Standard Annex #14, "Unicode Line Breaking Algorithm" [UAX14].
Grapheme_Cluster_Break E I See Unicode Standard Annex #29, "Unicode Text Segmentation" [UAX29]
Sentence_Break E I See Unicode Standard Annex #29, "Unicode Text Segmentation" [UAX29]
Word_Break E I See Unicode Standard Annex #29, "Unicode Text Segmentation" [UAX29]
Name_Alias M N Normative formal aliases for characters with erroneous names, as described in Chapter 4, Character Properties in [Unicode]. These aliases exactly match the formal aliases published in the Unicode Standard code charts.
used in Decomposition Mappings S N NormalizationCorrections lists code point differences for Normalization Corrigenda. For more information, see Unicode Standard Annex #15, "Unicode Normalization Forms" [UAX15].
Script C I Script values for use in regular expressions. For more information, see Unicode Standard Annex #24, "Unicode Script Property" [UAX24].
S I Data for producing (in combination with the simple case mappings from UnicodeData.txt) the full case mappings.
Unihan data files (for more information, see [UAX38])
E I The characters tagged with either kPrimaryNumeric, kAccountingNumeric, or kOtherNumeric are given the property value Numeric_Type=Numeric, and the Numeric_Value indicated in those tags.

Most characters have these numeric properties based on values from UnicodeData.txt. See Numeric_Type.

Unicode_Radical_Stroke M I The Unicode radical-stroke count, based on the tag kRSUnicode.
Lowercase B I Characters with the Lowercase property. For more information, see Chapter 4, Character Properties in [Unicode].

Generated from: Ll + Other_Lowercase

Uppercase B I Characters with the Uppercase property. For more information, see Chapter 4, Character Properties in [Unicode].

Generated from: Lu + Other_Uppercase

Cased B I Characters which are considered to be either uppercase, lowercase or titlecase characters. This property is not identical to the Changes_When_Casemapped property. For more information, see D120 in Section 3.13, Default Case Algorithms in [Unicode].

Generated from: Lowercase + Uppercase + Lt

Case_Ignorable B I Characters which are ignored for casing purposes. For more information, see D121 in Section 3.13, Default Case Algorithms in [Unicode].

Generated from: Mn + Me + Cf + Lm + Sk + Word_Break=MidLetter + Word_Break=MidNumLet

Changes_When_Lowercased B I Characters whose normalized forms are not stable under a toLowercase mapping. For more information, see D124 in Section 3.13, Default Case Algorithms in [Unicode].

Generated from: toLowercase(toNFD(X)) != toNFD(X)

Changes_When_Uppercased B I Characters whose normalized forms are not stable under a toUppercase mapping. For more information, see D125 in Section 3.13, Default Case Algorithms in [Unicode].

Generated from: toUppercase(toNFD(X)) != toNFD(X)

Changes_When_Titlecased B I Characters whose normalized forms are not stable under a toTitlecase mapping. For more information, see D126 in Section 3.13, Default Case Algorithms in [Unicode].

Generated from: toTitlecase(toNFD(X)) != toNFD(X)

Changes_When_Casefolded B I Characters whose normalized forms are not stable under case folding. For more information, see D127 in Section 3.13, Default Case Algorithms in [Unicode].

Generated from: toCasefold(toNFD(X)) != toNFD(X)

Changes_When_Casemapped B I Characters which may change when they undergo case mapping. For more information, see D128 in Section 3.13, Default Case Algorithms in [Unicode].

Generated from: Changes_When_Lowercased(X) or Changes_When_Uppercased(X) or Changes_When_Titlecased(X)

Alphabetic B I Characters with the Alphabetic property. For more information, see Chapter 4, Character Properties in [Unicode].

Generated from: Lu + Ll + Lt + Lm + Lo + Nl + Other_Alphabetic

Default_Ignorable_Code_Point B N For programmatic determination of default ignorable code points. New characters that should be ignored in rendering (unless explicitly supported) will be assigned in these ranges, permitting programs to correctly handle the default rendering of such characters when not otherwise supported. For more information, see the FAQ Display of Unsupported Characters, and Section 5.21, Default Ignorable Code Points in [Unicode].

Generated from
+ Cf (format characters)
+ Variation_Selector
- White_Space
- FFF9..FFFB (annotation characters)
- 0600..0603, 06DD, 070F, 110BD (exceptional Cf characters that should be visible)

Grapheme_Base B I For programmatic determination of grapheme cluster boundaries. For more information, see Unicode Standard Annex #29, "Unicode Text Segmentation" [UAX29].

Generated from: [0..10FFFF] - Cc - Cf - Cs - Co - Cn - Zl - Zp - Grapheme_Extend

Grapheme_Extend B I For programmatic determination of grapheme cluster boundaries. For more information, see Unicode Standard Annex #29, "Unicode Text Segmentation" [UAX29].

Generated from: Me + Mn + Other_Grapheme_Extend

Note: Depending on an application's interpretation of Co (private use), they may be either in Grapheme_Base, or in Grapheme_Extend, or in neither.

Grapheme_Link (Deprecated as of 5.0.0) B I Formerly proposed for programmatic determination of grapheme cluster boundaries.

Generated from: Canonical_Combining_Class=Virama

Math B I Characters with the Math property. For more information, see Chapter 4, Character Properties in [Unicode].

Generated from: Sm + Other_Math

ID_Start B I Used to determine programming identifiers, as described in Unicode Standard Annex #31, "Unicode Identifier and Pattern Syntax" [UAX31].
ID_Continue B I
XID_Start B I
XID_Continue B I
Full_Composition_Exclusion B N Characters that are excluded from composition: those listed explicitly in CompositionExclusions.txt, plus the derivable sets of Singleton Decompositions and Non-Starter Decompositions, as documented in that data file.
(Deprecated as of 6.0.0)
B N Characters that expand to more than one character in the specified normalization form.
(Deprecated as of 6.0.0)
S N Characters that require extra mappings for closure under Case Folding plus Normalization Form KC. Characters marked with this property have a third field with the mapping in it.

The mapping is listed in Field 2.

Generated with the following, where Fold is defined as the default fold operation (excluding the Turkic-specific foldings):

b = NFKC(Fold(a));
c = NFKC(Fold(b));
if (c != b) add mapping from a to c
to the set of mappings that constitute the FC_NFKC_Closure list

Note: The FC_NFKC_Closure value is omitted in the data file if it is the same as the code point itself.

E N For property values, see Decompositions and Normalization. (Abbreviated names: NFD_QC, NFKD_QC, NFC_QC, NFKC_QC)
NFKC_Casefold S I Mapping from a character to the string produced by casefolding it, removing any Default_Ignorable_Code_Point=T characters, and converting to NFKC form. (This set of transforms is then repeated, to deal with certain edge cases.) A mapping designed for best behavior when doing caseless matching of strings interpreted as identifiers. (Abbreviated name: NFKC_CF)

For the definition of the related string transform toNFKC_Casefold() based on this mapping, see Section 3.13, Default Case Algorithms in [Unicode].

The mapping is listed in Field 2.

Changes_When_NFKC_Casefolded B I Characters which are not identical to their NFKC_Casefold mapping.

Generated from: (cp != NFKC_CaseFold(cp))

ASCII_Hex_Digit B N ASCII characters commonly used for the representation of hexadecimal numbers.
Bidi_Control B N Format control characters which have specific functions in the Unicode Bidirectional Algorithm [UAX9].
Dash B I Punctuation characters explicitly called out as dashes in the Unicode Standard, plus their compatibility equivalents. Most of these have the General_Category value Pd, but some have the General_Category value Sm because of their use in mathematics.
Deprecated B N For a machine-readable list of deprecated characters. No characters will ever be removed from the standard, but the usage of deprecated characters is strongly discouraged.
Diacritic B I Characters that linguistically modify the meaning of another character to which they apply. Some diacritics are not combining characters, and some combining characters are not diacritics.
Extender B I Characters whose principal function is to extend the value or shape of a preceding alphabetic character. Typical of these are length and iteration marks.
Hex_Digit B I Characters commonly used for the representation of hexadecimal numbers, plus their compatibility equivalents.
Hyphen (Stabilized as of 4.0.0; Deprecated as of 6.0.0) B I Dashes which are used to mark connections between pieces of words, plus the Katakana middle dot. The Katakana middle dot functions like a hyphen, but is shaped like a dot rather than a dash.
Ideographic B I Characters considered to be CJKV (Chinese, Japanese, Korean, and Vietnamese) ideographs. This property roughly defines the class of "Chinese characters" and does not include characters of other logographic scripts such as Cuneiform or Egyptian Hieroglyphs.
IDS_Binary_Operator B N Used in Ideographic Description Sequences.
IDS_Trinary_Operator B N Used in Ideographic Description Sequences.
Join_Control B N Format control characters which have specific functions for control of cursive joining and ligation.
Logical_Order_Exception B N There are a small number of characters that do not use logical order. These characters require special handling in most processing. A small number of spacing vowel letters occurring in certain Southeast Asian scripts such as Thai and Lao, which use a visual order display model. These letters are stored in text ahead of syllable-initial consonants, and require special handling for processes such as searching and sorting.
Noncharacter_Code_Point B N Code points permanently reserved for internal use.
Other_Alphabetic B C Used in deriving the Alphabetic property.
Other_Default_Ignorable_Code_Point B C Used in deriving the Default_Ignorable_Code_Point property.
Other_Grapheme_Extend B C Used in deriving  the Grapheme_Extend property.
Other_ID_Continue B C Used for backward compatibility of ID_Continue.
Other_ID_Start B C Used for backward compatibility of ID_Start.
Other_Lowercase B C Used in deriving the Lowercase property.
Other_Math B C Used in deriving the Math property.
Other_Uppercase B C Used in deriving the Uppercase property.
Pattern_Syntax B N Used for pattern syntax as described in Unicode Standard Annex #31, "Unicode Identifier and Pattern Syntax" [UAX31].
Pattern_White_Space B N
Quotation_Mark B I Punctuation characters that function as quotation marks.
Radical B N Used in Ideographic Description Sequences.
Soft_Dotted B N Characters with a "soft dot", like i or j. An accent placed on these characters causes the dot to disappear. An explicit dot above can be added where required, such as in Lithuanian.
STerm B I Sentence Terminal. Used in Unicode Standard Annex #29, "Unicode Text Segmentation" [UAX29].
Terminal_Punctuation B I Punctuation characters that generally mark the end of textual units.
Unified_Ideograph B N A property which specifies the exact set of Unified CJK Ideographs in the standard. This set excludes CJK Compatibility Ideographs (which have canonical decompositions to Unified CJK Ideographs), as well as characters from the CJK Symbols and Punctuation block. The property is used in the definition of Ideographic Description Sequences.
Variation_Selector B N Indicates characters that are Variation Selectors. For details on the behavior of these characters, see StandardizedVariants.html, Section 16.4, Variation Selectors in [Unicode], and Unicode Standard Annex #37, "Unicode Ideographic Variation Database" [UTS37].
White_Space B N Spaces, separator characters and other control characters which should be treated by programming languages as "white space" for the purpose of parsing elements. See also Line_Break, Grapheme_Cluster_Break, Sentence_Break, and Word_Break, which classify space characters and related controls somewhat differently for particular text segmentation contexts.

Note: ZERO WIDTH SPACE and ZERO WIDTH NO-BREAK SPACE are not included, because their functions are restricted to line-break control. Their names are unfortunately misleading in this respect.

Note: There are other senses of "whitespace" that encompass a different set of characters.

Name M N (1) These names match exactly the names published in the code charts of the Unicode Standard. The derived Hangul Syllable names are omitted from this file; see Jamo.txt for their derivation.
General_Category E N (2) This is a useful breakdown into various character types which can be used as a default categorization in implementations. For the property values, see General Category Values.
Canonical_Combining_Class N N (3) The classes used for the Canonical Ordering Algorithm in the Unicode Standard. This property could be considered either an enumerated property or a numeric property: the principal use of the property is in terms of the numeric values. For the property value names associated with different numeric values, see DerivedCombiningClass.txt and Canonical Combining Class Values.
Bidi_Class E N (4) These are the categories required by the Unicode Bidirectional Algorithm. For the property values, see Bidirectional Class Values. For more information, see Unicode Standard Annex #9, "The Unicode Bidirectional Algorithm" [UAX9].

The default property values depend on the code point, and are explained in DerivedBidiClass.txt

N (5) This field contains both values, with the type in angle brackets. The decomposition mappings exactly match the decomposition mappings published with the character names in the Unicode Standard. For more information, see Character Decomposition Mappings.
N (6) If the character has the property value Numeric_Type=Decimal, then the Numeric_Value of that digit is represented with an integer value (limited to the range 0..9) in fields 6, 7, and 8. Characters with the property value Numeric_Type=Decimal are restricted to digits which can be used in a decimal radix positional numeral system and which are encoded in the standard in a contiguous ascending range 0..9. See the discussion of decimal digits in Chapter 4, Character Properties in [Unicode].
N (7) If the character has the property value Numeric_Type=Digit, then the Numeric_Value of that digit is represented with an integer value (limited to the range 0..9) in fields 7 and 8, and field 6 is null. This covers digits that need special handling, such as the compatibility superscript digits.
N (8) If the character has the property value Numeric_Type=Numeric, then the Numeric_Value of that character is represented with a positive or negative integer or rational number in this field, and fields 6 and 7 are null. This includes fractions such as, for example, "1/5" for U+2155 VULGAR FRACTION ONE FIFTH.

Some characters have these properties based on values from the Unihan data files. See Numeric_Type, Han.

Bidi_Mirrored B N (9) If the character is a "mirrored" character in bidirectional text, this field has the value "Y"; otherwise "N". See Section 4.7, Bidi Mirrored—Normative of [Unicode]. Do not confuse this with the Bidi_Mirroring_Glyph property.
Unicode_1_Name M I (10) Old name as published in Unicode 1.0. This name is only provided when it is significantly different from the current name for the character. The value of field 10 for control characters does not always match the Unicode 1.0 names. Instead, field 10 contains ISO 6429 names for control functions, for printing in the code charts.
ISO_Comment (Obsolete as of 5.2.0; Deprecated and Stabilized as of 6.0.0) M I (11) ISO 10646 comment field. It was used for notes that appeared in parentheses in the 10646 names list, or contained an asterisk to mark an Annex P note.

As of Unicode 5.2.0, this field no longer contains any non-null values.

Simple_Uppercase_Mapping S N (12) Simple uppercase mapping (single character result).
If a character is part of an alphabet with case distinctions, and has a simple uppercase equivalent, then the uppercase equivalent is in this field. The simple mappings have a single character result, where the full mappings may have multi-character results. For more information, see Case and Case Mapping.
Simple_Lowercase_Mapping S N (13) Simple lowercase mapping (single character result).
Simple_Titlecase_Mapping S N (14) Simple titlecase mapping (single character result).

Note: If this field is null, then the Simple_Titlecase_Mapping is the same as the Simple_Uppercase_Mapping for this character.


5.4 Derived Extracted Properties

A number of Unicode character properties have been separated out, reformatted, and listed in range format, one property per file. These files are located under the extracted directory of the UCD. The exact list of derived extracted files and the extracted properties they represent are given in Table 10.

The derived extracted files are provided purely as a reformatting of data for properties specified in other data files. In case of any inadvertant mismatch between the primary data files specifying those properties and these lists of extracted properties, the primary data files are taken as definitive.

Table 10. Extracted Properties

File Status Property Extracted from
DerivedBidiClass.txt N Bidi_Class UnicodeData.txt, field 4
DerivedBinaryProperties.txt N Bidi_Mirrored UnicodeData.txt, field 9
DerivedCombiningClass.txt N Canonical_Combining_Class UnicodeData.txt, field 3
DerivedDecompositionType.txt N/I Decomposition_Type the <tag> in UnicodeData.txt, field 5
DerivedEastAsianWidth.txt I East_Asian_Width EastAsianWidth.txt, field 1
DerivedGeneralCategory.txt N General_Category UnicodeData.txt, field 2
DerivedJoiningGroup.txt N Joining_Group ArabicShaping.txt, field 2
DerivedJoiningType.txt N Joining_Type ArabicShaping.txt, field 1
DerivedLineBreak.txt N Line_Break LineBreak.txt, field 1
DerivedNumericType.txt N Numeric_Type UnicodeData.txt, fields 6 through 8
DerivedNumericValues.txt N Numeric_Value UnicodeData.txt, field 8

For the extraction of Decomposition_Type, characters with canonical decomposition mappings in field 5 of UnicodeData.txt have no tag. For those characters, the extracted value is Decomposition_Type=Canonical. For characters with compatibility decomposition mappings, there are explicit tags in field 5, and the value of Decomposition_Type is equivalent to those tags. The value Decomposition_Type=Canonical is normative. Other values for Decomposition_Type are informative.

Numeric_Value is extracted based on the actual numeric value of the data in field 8 of UnicodeData.txt or the values of the kPrimaryNumeric, kAccountingNumeric, or kOtherNumeric tags, for characters listed in the Unihan data files.

Numeric_Type is extracted as follows. If fields 6, 7, and 8 in UnicodeData.txt are all non-empty, then Numeric_Type=Decimal. Otherwise, if fields 7 and 8 are both non-empty, then Numeric_Type=Digit. Otherwise, if field 8 is non-empty, then Numeric_Type=Numeric. For characters listed in the Unihan data files, Numeric_Type=Numeric for characters that have kPrimaryNumeric, kAccountingNumeric, or kOtherNumeric tags. The default value is Numeric_Type=None.

5.53.1 Contributory Properties

Contributory properties contain sets of exceptions used in the generation of other properties derived from them. The contributory properties specifically concerned with identifiers and casing contribute to the maintenance of stability guarantees for properties and/or to invariance relationships between related properties. Other contributory properties are simply defined as a convenience for property derivation.

Most contributory properties have names using the pattern "Other_XXX" and are used to derive the corresponding "XXX" property. For example, the Other_Alphabetic property is used in the derivation of the Alphabetic property.

Contributory properties are typically defined in PropList.txt and the corresponding derived property is then listed in DerivedCoreProperties.txt.

Jamo_Short_Name is an unusual contributory property, both in terms of its name and how it is used. It is defined in its own property file, Jamo.txt, and is used to derive the Name property value for Hangul syllable characters, according to the rules spelled out in Section 3.12, Conjoining Jamo Behavior in [Unicode].

Contributory is considered to be a distinct status for a Unicode character property. Contributory properties are neither normative nor informative. This distinct status is marked in the property table.

Contributory properties are incomplete by themselves and are not intended for independent use. For example, an API returning Unicode property values should implement the derived core properties such as Alphabetic or Default_Ignorable_Code_Point, rather than the corresponding contributory properties, Other_Alphabetic or Other_Default_Ignorable_Code_Point.

5.6 Case and Case Mapping

Case for bicameral scripts and case mapping of characters are complicated topics in the Unicode Standard—both because of their inherent algorithmic complexity and because of the number of characters and special edge cases involved.

This section provides a brief roadmap to discussions about these topics, and specifications and definitions in the standard, as well as explaining which case-related properties are defined in the UCD.

Section 3.13, Default Case Algorithms in [Unicode] provides formal definitions for a number of case-related concepts (cased, case-ignorable, ...), for case conversion (toUppercase(X), ...), and for case detection (isUppercase(X), ...). It also provides the formal definition of caseless matching for the standard, taking normalization into account.

Section 4.2, Case—Normative in [Unicode] introduces case and case mapping properties. Table 4-1, Sources for Case Mapping Information in [Unicode] describes the kind of case-related information that is available in various data files of the UCD. Table 11 lists those data files again, giving the explicit list of case-related properties defined in each. The link on each property leads its description in the Table 9, Property Table above.

Table 11. UCD Files and Case Properties

File Name Case Properties
UnicodeData.txt Simple_Uppercase_Mapping, Simple_Lowercase_Mapping, Simple_Titlecase_Mapping
SpecialCasing.txt Uppercase_Mapping, Lowercase_Mapping, Titlecase_Mapping
CaseFolding.txt Simple_Case_Folding, Case_Folding
DerivedCoreProperties.txt Uppercase, Lowercase, Cased, Case_Ignorable, Changes_When_Lowercased, Changes_When_Uppercased, Changes_When_Titlecased, Changes_When_Casefolded, Changes_When_Casemapped
DerivedNormalizationProps.txt NFKC_Casefold, Changes_When_NFKC_Casefolded
PropList.txt Soft_Dotted, Other_Uppercase, Other_Lowercase

For compatibility with existing parsers, UnicodeData.txt only contains case mappings for characters where they constitute one-to-one mappings; it also omits information about context-sensitive case mappings. Information about these special cases can be found in the separate data file, SpecialCasing.txt, expressed as separate properties.

Section 5.18, Case Mappings, in [Unicode] discusses various implementation issues for handling case, including language-specific case mapping, as for Greek and for Turkish. That section also describes case folding in particular detail.

The special casing conditions associated with case mapping for Greek, Turkish, and Lithuanian are specified in an additional field in SpecialCasing.txt. For example, the lowercase mapping for sigma in Greek varies according to its position in a word. The condition list does not constitute a formal character property in the UCD, because it is a statement about the context of occurrence of casing behavior for a character or characters, rather than a semantic attribute of those characters. Versions of the UCD from Version 3.2.0 to Version 5.0.0 did list property aliases for Special_Case_Condition (scc), but this was determined to be an error when the UCD was analyzed for representation in XML; consequently, the Special_Case_Condition property aliases were removed as of Version 5.1.0.

Caseless matching is of particular concern for a number of text processing algorithms, so is also discussed at some length in Unicode Standard Annex #31, "Unicode Identifier and Pattern Syntax" [UAX31] and in Unicode Technical Standard #10, "Unicode Collation Algorithm" [UTS10].

Further information about locale-specific casing conventions can be found in the Unicode Common Locale Data Repository [CLDR].

5.7 Property Value Lists

The following subsections give summaries of property values for certain Enumeration properties. Other property values are documented in other, topically-specific annexes; for example, the Line_Break property values are documented in Unicode Standard Annex #14, "Unicode Line Breaking Algorithm" [UAX14] and the various segmentation-related property values are documented in Unicode Standard Annex #29, "Unicode Text Segmentation" [UAX29].

5.7.1 General Category Values

The General_Category property of a code point provides for the most general classification of that code point. It is usually determined based on the primary characteristic of the assigned character for that code point. For example, is the character a letter, a mark, a number, punctuation, or a symbol, and if so, of what type? Other General_Category values define the classification of code points which are not assigned to regular graphic characters, including such statuses as private-use, control, surrogate code point, and reserved unassigned.

Many characters have multiple uses, and not all such cases can be captured entirely by the General_Category value. For example, the General_Category value of Latin, Greek, or Hebrew letters does not attempt to cover (or preclude) the numerical use of such letters as Roman numerals or in other numerary systems. Conversely, the General_Category of ASCII digits 0..9 as Nd (decimal digit) neither attempts to cover (or preclude) the occasional use of these digits as letters in various orthographies. The General_Category is simply the first-order, most usual categorization of a character.

For more information about the General_Category property, see Chapter 4, Character Properties in [Unicode].

The values in the General_Category field in UnicodeData.txt make use of the short, abbreviated property value aliases for General_Category. For convenience in reference, Table 12 lists all the abbreviated and long value aliases for General_Category values, reproduced from PropertyValueAliases.txt, along with a brief description of each category.

Table 12. General_Category Values

Abbr Long Description
Lu Uppercase_Letter an uppercase letter
Ll Lowercase_Letter a lowercase letter
Lt Titlecase_Letter a digraphic character, with first part uppercase
Lm Modifier_Letter a modifier letter
Lo Other_Letter other letters, including syllables and ideographs
Mn Nonspacing_Mark a nonspacing combining mark (zero advance width)
Mc Spacing_Mark a spacing combining mark (positive advance width)
Me Enclosing_Mark an enclosing combining mark
Nd Decimal_Number a decimal digit
Nl Letter_Number a letterlike numeric character
No Other_Number a numeric character of other type
Pc Connector_Punctuation a connecting punctuation mark, like a tie
Pd Dash_Punctuation a dash or hyphen punctuation mark
Ps Open_Punctuation an opening punctuation mark (of a pair)
Pe Close_Punctuation a closing punctuation mark (of a pair)
Pi Initial_Punctuation an initial quotation mark
Pf Final_Punctuation a final quotation mark
Po Other_Punctuation a punctuation mark of other type
Sm Math_Symbol a symbol of primarily mathematical use
Sc Currency_Symbol a currency sign
Sk Modifier_Symbol a non-letterlike modifier symbol
So Other_Symbol a symbol of other type
Zs Space_Separator a space character (of various non-zero widths)
Zl Line_Separator U+2028 LINE SEPARATOR only
Zp Paragraph_Separator U+2029 PARAGRAPH SEPARATOR only
Cc Control a C0 or C1 control code
Cf Format a format control character
Cs Surrogate a surrogate code point
Co Private_Use a private-use character
Cn Unassigned a reserved unassigned code point or a noncharacter

Note that the value gc=Cn does not actually occur in UnicodeData.txt, because that data file does not list unassigned code points.

Characters with the quotation-related General_Category values Pi or Pf may behave like opening punctuation (gc=Ps) or closing punctuation (gc=Pe), depending on usage and quotation conventions.

The symbol "L&" is used to stand for any combination of uppercase, lowercase or titlecase letters (Lu, Ll, or Lt), in the first part of comments in the data files. The LC value for the General_Category property, as documented in PropertyValueAliases.txt also stands for uppercase, lowercase or titlecase letters.

The Unicode Standard does not assign non-default property values to control characters (gc=Cc), except for certain well-defined exceptions involving the Unicode Bidirectional Algorithm, the Unicode Line Breaking Algorithm, and Unicode Text Segmentation. Also, implementations will usually assign behavior to certain line breaking control characters—most notably U+000D and U+000A (CR and LF)—according to platform conventions. See Section 5.8, Newline Guidelines in [Unicode] for more information.

5.7.2 Bidirectional Class Values

The values in the Bidi_Class field in UnicodeData.txt make use of the short, abbreviated property value aliases for Bidi_Class. For convenience in reference, Table 13 lists all the abbreviated and long value aliases for Bidi_Class values, reproduced from PropertyValueAliases.txt, along with a brief description of each category.

Table 13. Bidi_Class Values

Abbr Long Description
L Left_To_Right any strong left-to-right character
LRE Left_To_Right_Embedding U+202A: the LR embedding control
LRO Left_To_Right_Override U+202D: the LR override control
R Right_To_Left any strong right-to-left (non-Arabic-type) character
AL Arabic_Letter any strong right-to-left (Arabic-type) character
RLE Right_To_Left_Embedding U+202B: the RL embedding control
RLO Right_To_Left_Override U+202E: the RL override control
PDF Pop_Directional_Format U+202C: terminates an embedding or override control
EN European_Number any ASCII digit or Eastern Arabic-Indic digit
ES European_Separator plus and minus signs
ET European_Terminator a terminator in a numeric format context, includes currency signs
AN Arabic_Number any Arabic-Indic digit
CS Common_Separator commas, colons, and slashes
NSM Nonspacing_Mark any nonspacing mark
BN Boundary_Neutral most format characters, control codes, or noncharacters
B Paragraph_Separator various newline characters
S Segment_Separator various segment-related control codes
WS White_Space spaces
ON Other_Neutral most other symbols and punctuation marks

Please refer to Unicode Standard Annex #9, "The Unicode Bidirectional Algorithm" [UAX9] for an an explanation of the significance of these values when formatting bidirectional text.

5.7.3 Character Decomposition Mapping

The value of the Decomposition_Mapping property for a character is provided in field 5 of UnicodeData.txt. This is a string property, consisting of a sequence of one or more Unicode code points. The default value of the Decomposition_Mapping property is the code point of the character itself. The use of the default value for a character is indicated by leaving field 5 empty in UnicodeData.txt. Informally, the value of the Decomposition_Mapping property for a character is known simply as its decomposition mapping. When a character's decomposition mapping is other than the default value, the decomposition mapping is printed out explicitly in the names list for the Unicode code charts.

The prefixed tags supplied with a subset of the decomposition mappings generally indicate formatting information. Where no such tag is given, the mapping is canonical. Conversely, the presence of a formatting tag also indicates that the mapping is a compatibility mapping and not a canonical mapping. In the absence of other formatting information in a compatibility mapping, the tag is used to distinguish it from canonical mappings.

In some instances a canonical mapping or a compatibility mapping may consist of a single character. For a canonical mapping, this indicates that the character is a canonical equivalent of another single character. For a compatibility mapping, this indicates that the character is a compatibility equivalent of another single character.

The compatibility formatting tags used in the UCD are listed in Table 14.

Table 14. Compatibility Formatting Tags

Tag Description
<font> Font variant (for example, a blackletter form)
<noBreak> No-break version of a space or hyphen
<initial> Initial presentation form (Arabic)
<medial> Medial presentation form (Arabic)
<final> Final presentation form (Arabic)
<isolated> Isolated presentation form (Arabic)
<circle> Encircled form
<super> Superscript form
<sub> Subscript form
<vertical> Vertical layout presentation form
<wide> Wide (or zenkaku) compatibility character
<narrow> Narrow (or hankaku) compatibility character
<small> Small variant form (CNS compatibility)
<square> CJK squared font variant
<fraction> Vulgar fraction form
<compat> Otherwise unspecified compatibility character

Note: There is a difference between decomposition and the Decomposition_Mapping property. The Decomposition_Mapping property is a string property whose values (mappings) are defined in UnicodeData.txt, while the decomposition (also termed "full decomposition") is defined in Section 3.7, Decomposition in [Unicode] to use those mappings recursively.

Starting from Unicode 2.1.9, the decomposition mappings in UnicodeData.txt can be used to derive the full decomposition of any single character in canonical order, without the need to separately apply the Canonical Ordering Algorithm. However, canonical ordering of combining character sequences must still be applied in decomposition when normalizing source text which contains any combining marks.

The normalization of Hangul conjoining jamos and of Hangul syllables depends on algorithmic mapping, as specified in Section 3.12, Conjoining Jamo Behavior in [Unicode]. That algorithm specifies the full decomposition of all precomposed Hangul syllables, but effectively it is equivalent to the recursive application of pairwise decomposition mappings, as for all other Unicode characters. Formally, the Decomposition_Mapping property value for a Hangul syllable is the pairwise decomposition and not the full decomposition.

Each character with the Hangul_Syllable_Type value LVT will have a Decomposition_Mapping consisting of a character with an LV value and a character with a T value. Thus for U+CE31 the Decomposition_Mapping is <U+CE20, U+11B8>, rather than <U+110E, U+1173, U+11B8>.

5.7.4 Canonical Combining Class Values

The values in the Canonical_Combining_Class field in UnicodeData.txt are numerical values used in the Canonical Ordering Algorithm. Some of those numerical values also have explicit symbolic labels as property value aliases, to make their intended application more understandable. For convenience in reference, Table 15 lists all the long symbolic aliases for Canonical_Combining_Class values, reproduced from PropertyValueAliases.txt, along with a brief description of each category.

Table 15. Canonical_Combining_Class Values

Value Long Description
0 Not_Reordered Spacing and enclosing marks; also many vowel and consonant signs, even if nonspacing
1 Overlay Marks which overlay a base letter or symbol
7 Nukta Diacritic nukta marks in Brahmi-derived scripts
8 Kana_Voicing Hiragana/Katakana voicing marks
9 Virama Viramas
10   Start of fixed position classes
199   End of fixed position classes
200 Attached_Below_Left Marks attached at the bottom left
202 Attached_Below Marks attached directly below
204   Marks attached at the top bottom right
208   Marks attached to the left
210   Marks attached to the right
212   Marks attached at the top left
214 Attached_Above Marks attached directly above
216 Attached_Above_Right Marks attached at the top right
218 Below_Left Distinct marks at the bottom left
220 Below Distinct marks directly below
222 Below_Right Distinct marks at the bottom right
224 Left Distinct marks to the left
226 Right Distinct marks to the right
228 Above_Left Distinct marks at the top left
230 Above Distinct marks directly above
232 Above_Right Distinct marks at the top right
233 Double_Below Distinct marks subtending two bases
234 Double_Above Distinct marks extending above two bases
240 Iota_Subscript Greek iota subscript only

Some of the Canonical_Combining_Class values in the table are not currently used for any characters but are specified here for completeness. Some values do not have long symbolic aliases, but these two sets are not congruent. Do not assume that absence of a long symbolic alias implies non-use of a particular Canonical_Combining_Class. See DerivedCombiningClass.txt for a complete listing of the use of Canonical_Combining_Class values for any particular version of the UCD.

Combining marks with ccc=224 (Left) follow their base character in storage, as for all combining marks, but are rendered visually on the left side of them. For all past versions of the UCD and continuing with this version of the UCD, only two tone marks used in certain notations for Hangul syllables have ccc=224. Those marks are actually rendered visually on the left side of the preceding grapheme cluster, in the case of Hangul syllables resulting from sequences of conjoining jamos.

Those few instances of combining marks with ccc=Left should be distinguished from the far more numerous examples of left-side vowel signs and vowel letters in Brahmi-derived scripts. The Canonical_Combining_Class value is zero (Not_Reordered) for both ordinary, left-side (reordrant) vowel signs such as U+093F DEVANAGARI VOWEL SIGN I and for Thai-style left-side (Logical_Order_Exception=Yes) vowel letters such as U+0E40 THAI CHARACTER SARA E. The "Not_Reordered" of ccc=Not_Reordered refers to the behavior of the character in terms of the Canonical Ordering Algorithm as part of the definition of Unicode Normalization; it does not refer to any issues of visual reordering of glyphs involved in display and rendering. See "Canonical Ordering Algorithm" in Section 3.11, "Canonical Ordering Behavior" Normalization Forms in [Unicode].

5.7.5 Decompositions and Normalization

Decomposition is specified in Chapter 3, Conformance of [Unicode]. UAX #15, Unicode Normalization Forms [UAX15] That chapter also specifies the interaction between decomposition and normalization. That annex specifies how the decompositions defined in UnicodeData.txt are used to derive normalized forms of Unicode text.

A number of derived properties related to Unicode normalization are called the "Quick_Check" properties. These are defined to enable various optimizations for implementations of normalization, as explained in Section 9, Detecting Normalization Forms, in Unicode Standard Annex #15, "Unicode Normalization Forms" [UAX15]. The values for the four Quick_Check properties for all code points are listed in DerivedNormalizationProps.txt. The interpretations of the possible property values are summarized in Table 16.

Table 16. Quick_Check Property Values

Property Value Description
NFC_QC, NFKC_QC, NFD_QC, NFKD_QC No Characters that cannot ever occur in the respective normalization form.
NFC_QC, NFKC_QC Maybe Characters that may occur in the respective normalization, depending on the context.
NFC_QC, NFKC_QC, NFD_QC, NFKD_QC Yes All other characters. This is the default value for Quick_Check properties.

5.8 Property and Property Value Aliases

Both Unicode character properties themselves and their values are given symbolic aliases. The formal lists of aliases are provided so that well-defined symbolic values are available for XML formats of the UCD data, for regular expression property tests, and for other programmatic textual descriptions of Unicode data. The aliases for properties are defined in PropertyAliases.txt. The aliases for property values are defined in PropertyValueAliases.txt.

Table 17. Alias Files in the UCD

File Name Status Description
PropertyAliases.txt N Names and abbreviations for properties
PropertyValueAliases.txt N Names and abbreviations for property values

Aliases are defined as ASCII-compatible identifiers, using only uppercase or lowercase A-Z, digits, and underscore "_". Case is not significant when comparing aliases, but the preferred form used in the data files for longer aliases is to titlecase them.

Aliases may be translated in appropriate environments, and additional aliases may be useful in certain contexts. There is no requirement that only the aliases defined in the alias files of the UCD be used when referring to Unicode character properties or their values; however, their use is recommended for interoperability in data formats or in programmatic contexts.

Aliases are not provided for provisional properties. This results from the fact that there are stability guarantees for property aliases and property value aliases, but no stability guarantees for provisional properties or other provisional data files.

5.8.1 Property Aliases

In PropertyAliases.txt, the first field specifies an abbreviated symbolic name for the property, and the second field specifies the long symbolic name for the property. These are the preferred aliases. Additional aliases for a few properties are specified in the third or subsequent fields.

Aliases for normative and informative properties defined in the Unihan data files are included in PropertyAliases.txt, beginning with Version 5.2.

The long symbolic name alias is self-descriptive, and is treated as the official name of a Unicode character property. For clarity it is used whenever possible when referring to that property in this annex and elsewhere in the Unicode Standard. For example: "The Line_Break property is discussed in Unicode Standard Annex #14, "Unicode Line Breaking Algorithm" [UAX14]."

The abbreviated symbolic name alias is short and less mnemonic, but is useful for expressions such as "lb=BA" in data or in other contexts where the meaning is clear.

The property aliases specified in PropertyAliases.txt constitute a unique name space. When using these symbolic values, no alias for one property will match an alias for another property.

5.8.2 Property Value Aliases

In PropertyValueAliases.txt, the first field contains the abbreviated alias for a Unicode property, the second field specifies an abbreviated symbolic name for a value of that property, and the third field specifies the long symbolic name for that value of that property. These are the preferred aliases. Additional aliases for some property values may be specified in the fourth or subsequent fields. For example, for binary properties, the abbreviated alias for the True value is "Y", and the long alias is "Yes", but each entry also specifies "T" and "True" as additional aliases for that value, as shown in Table 18.

Table 18. Binary Property Value Aliases

Long Abbreviated Other Aliases
Yes Y True, T
No N False, F

Not every property value has an associated alias. Property value aliases are typically supplied for catalog and enumeration properties, which have well-defined, enumerated values. It does not make sense to specify property value aliases, for example, for the Numeric_Value property, whose value could be any number, or for a string property such as Simple_Lowercase_Mapping, whose values are mappings from one code point to another.

The Canonical_Combining_Class property requires special handling in PropertyValueAliases.txt. The values of this property are numeric, but they comprise a closed, enumerated set of values. The more important of those values are given symbolic name aliases. In PropertyValueAliases.txt, the second field provides the numeric value, while the third field contains the abbreviated symbolic name alias and the fourth field contains the long symbolic name alias for that numeric value. For example:

ccc; 230; A    ; Above
ccc; 232; AR   ; Above_Right

Taken by themselves, property value aliases do not constitute a unique name space. The abbreviated aliases, in particular, are often re-used as aliases for values for different properties. All of the binary property value aliases, for example, make use of the same "Y", "Yes", "T", "True" symbols. Property value aliases may also overlap the symbols used for property aliases. For example, "Sc" is the abbreviated alias for the "Currency_Symbol" value of the General_Category value, but it is also the abbreviated alias for the Script property. However, the aliases for values for any single property are always unique within the context of that property. That means that expressions that combine a property alias and a property value alias, such as "lb=BA" or "gc=Sc" always refer unambiguously just to one value of one given property, and will not match any other value of any other property.

The property value alias entries for three properties, Age, Block, and Joining_Group, make use of a special metavalue "n/a" in the field for the abbreviated alias. This should be understood as meaning that no abbreviated alias is defined for that value for that property, rather than as an alias per se.

In a few cases, because of longstanding legacy practice in referring to values of a property by short identifiers, the abbreviated alias and the long alias are the same. This can be seen, for example, in some property value aliases for the Line_Break property and the Grapheme_Cluster_Break property.

5.9 Matching Rules

When matching Unicode character property names and values, it is strongly recommended that all Property and Property Value Aliases be recognized. For best results in matching, rather than using exact binary comparisons, the following loose matching rules should be observed.

Numeric Property Values

For all numeric properties, and for properties such as Unicode_Radical_Stroke which are constructed from combinations of numeric values, use loose matching rule UAX44-LM1 when comparing property values.

UAX44-LM1. Apply numeric equivalences.

Character Names

Unicode character names constitute a special case. Formally, they are values of the Name property. While each Unicode character name for an assigned character is guaranteed to be unique, names are assigned in such a way that the presence or absence of spaces cannot be used to distinguish them. Furthermore, implementations sometimes create identifiers from Unicode character names by inserting underscores for spaces. For best results in comparing Unicode character names, use loose matching rule UAX44-LM2.

UAX44-LM2. Ignore case, whitespace, underscore ('_'), and all medial hyphens except the hyphen in U+1180 HANGUL JUNGSEONG O-E.

In this rule "medial hyphen" is to be construed as a hyphen occurring immediately between two letters in the normative Unicode character name, as published in the Unicode names list, and not to any hyphen that may transiently occur medially as a result of removing whitespace before removing hyphens in a particular implementation of matching. Thus the hyphen in the name U+10089 LINEAR B IDEOGRAM B107M HE-GOAT is medial, and should be ignored in loose matching, but the hyphen in the name U+0F39 TIBETAN MARK TSA -PHRU is not medial, and should not be ignored in loose matching.

An implementation of this loose matching rule can obtain the correct results when comparing two strings by doing the following three operations, in order:

  1. remove all medial hyphens (except the medial hyphen in the name for U+1180)
  2. remove all whitespace and underscore characters
  3. apply toLowercase() to both strings

After applying these three operations, if the two strings compare binary equal, then they are considered to match.

This is a logical statement of how the rule works. If programmed carefully, an implementation of the matching rule can transform the strings in a single pass. It is also possible to compare two name strings for loose matching while transforming each string incrementally.

Loose matching rule UAX44-LM2 is also appropriate for matching formal name aliases and the names of named character sequences, which share the namespace (and matching behavior) of Unicode character names.

Symbolic Values

Property aliases and property value aliases are symbolic values. When comparing them, use loose matching rule UAX44-LM3.

UAX44-LM3. Ignore case, whitespace, underscore ('_'), and hyphens, and any initial prefix string "is".

Loose matching is generally appropriate for the property values of Catalog, Enumeration, and Binary properties, which have symbolic aliases defined for their values. Loose matching should not be done for the property values of String properties, which do not have symbolic aliases defined for their values; exact matching for String property values is important, as case distinctions or other distinctions in those values may be significant.

For loose matching of symbolic values, an initial prefix string "is" is ignored. The reason for this is that APIs returning property values are often named using the convention of prefixing "is" (or "Is" or "Is_", and so forth) to a property value. Ignoring any initial "is" on a symbolic value during loose matching is likely to produce the best results in application areas such as regex. Removal of an initial "is" string for a loose matching comparison only needs to be done once for a symbolic value, and need not be tested recursively. There are no property aliases or property value aliases of the form "isisisisistooconvoluted" defined just to test implementation edge cases.

Existing and future property aliases and property value aliases are guaranteed to be unique within their relevant namespaces, even if an initial prefix string "is" is ignored. The existing cases of note for aliases that do start with "is" are: dt=Iso (Decomposition_Type=Isolated) and lb=IS. The Decomposition_Type value alias does not cause any problem, because there is no contrasting value alias dt=o (Decomposition_Type=olated). For lb=IS, note that the "IS" is the entire property value alias, and is not a prefix. There is no null value for the Line_Break property for it to contrast with, but implementations of loose matching should be careful of this edge case, so that "lb=IS" is not misinterpreted as matching a null value.

Implementations sometimes use other syntactic constructs that interact with loose matching. For example, the property matching expression \p{L} may be defaulted to refer to the Unicode General_Category property: \p{General_Category=L}. For more information about the use of property values in regular expressions and other environments, see Section 1.2, Properties, in Unicode Technical Standard #18, "Unicode Regular Expressions" [UTS18]

5.10 Invariants

Property values in the UCD may be subject to correction in subsequent versions of the standard, as errors are found. Also, some multi-valued properties such as Line_Break or Word_Break may have additional values defined for them. However, some property values and some aspects of the file formats are considered invariant. This section documents such invariants.

5.10.1 Character Property Invariants

All formally guaranteed invariants for properties or property values are described in the Unicode Character Encoding Stability Policy [Stability]. That policy and the list of invariants it enumerates are maintained outside the context of the Unicode Standard per se. They are not part of the standard, but rather are constraints on what can and cannot change in the standard between versions, and on what decisions the Unicode Technical Committee can and cannot take regarding the standard.

In addition to the formally guaranteed invariants described in the Unicode Character Encoding Stability Policy, this section notes a few additional points regarding character property invariants in the UCD.

Some character properties are simply considered immutable: once assigned, they are never changed. For example, a character's name is immutable, because of its importance in exact identification of the character. The Canonical_Combining_Class and Decomposition_Mapping of a character are immutable, because of their importance to the stability of the Unicode Normalization Algorithm [UAX15].

The list of immutable character properties is shown in Table 19.

Table 19. Immutable Properties

Property Name Abbr Name
Name na
Jamo_Short_Name jsn
Canonical_Combining_Class ccc
Decomposition_Mapping dm
Pattern_Syntax Pat_Syn
Pattern_White_Space Pat_WS

In some cases, a property is not immutable, but the list of possible values that it can have is considered invariant. For example, while at least some General_Category values are subject to change and correction, the enumerated set of possible values that the General_Category property can have is fixed and cannot be added to in the future.

All characters other than those of General_Category M* are guaranteed to have Canonical_Combining_Class=0. Currently it is also true that all characters other than those of General_Category Mn have Canonical_Combining_Class=0. However, the more constrained statement is not a guaranteed invariant; it is possible that some new character of General_Category Me or Mc could be given a non-zero value for Canonical_Combining_Class in the future.

In Unicode 4.0 and thereafter, the General_Category value Decimal_Number (Nd), and the Numeric_Type value Decimal (de) are defined to be co-extensive; that is, the set of characters having General_Category=Nd will always be the same as the set of characters having NumericType=de.

5.10.2 UCD File Format Invariants

There are also some constraints on allowable change in the file formats for UCD files. In general, the file format conventions are changed as little as possible, to minimize the impact on implementations which parse the machine-readable data files. However, some of the constraints on allowable file format change go beyond conservatism in format and instead have the status of invariants. These guarantees apply in particular to UnicodeData.txt, the very first data file associated with the UCD.

The number and order of the fields in UnicodeData.txt is fixed. Any additional information about character properties to be added to the UCD in the future will appear in separate data files, rather than being added as an additional field to UnicodeData.txt or by reinterpretation of any of the existing fields.

5.10.3 Invariants in Implementations

Applications may wish to take the various character property and file format invariants into account when choosing how to implement character properties.

The Canonical_Combining_Class offers a good example. The character property invariants regarding Canonical_Combining_Class guarantee that values, once assigned, will never change, and that all values used will be in the range 0..255. This means that the Canonical_Combining_Class can be safely implemented in an unsigned byte and that any value stored in a table for an existing character will not need to be updated dynamically for a later version.

In practice, for Canonical_Combining_Class far fewer than 256 values are used. Unicode 3.0 used 53 values; Unicode 3.1 through Unicode 4.1 used 54 values; and Unicode 5.0 through Unicode 5.1 used 55 values. New, non-zero Canonical_Combining_Class values are seldom added to the standard. (For details about this history, see DerivedCombiningClass.txt.) Implementations may take advantage of this fact for compression, because only the ordering of the non-zero values, and not their absolute values, matters for the Canonical Ordering Algorithm. In principle, it would be possible for up to 256 values to be used in the future, but the chances of the actual number of values exceeding 128 are remote at this point. There are implementation advantages in restricting the number of internal class values to 128—for example, the ability to use signed bytes without implicit widening to ints in Java.

5.11 Validation

The Unicode character property values in the UCD files can be validated by means of regular expressions. Such validation can also be useful in testing of implementations that return property values. The method of validation depends on the type of property, as described below. These expressions use Perl syntax, but may of course be converted to other formal conventions for use with other regular expression engines.

The regular expressions which are appropriate for validation of particular properties may change in each subsequent version of the UCD. However, because of stability guarantees for character property aliases, these regular expressions for one version of the Unicode Standard will match valid values for previous versions of the standard.

5.11.1 Enumerated and Binary Properties

Enumerated and binary character properties can be validated by generating a regular expression using the PropertyValueAliases.txt file. Because enumerated properties have a defined list of possible values, the validating regular expression simply ORs together all of the possible values. Binary properties are a special case of enumerated property, with a predefined very short list of possible values.

For example, to validate the East_Asian_Width property in the UCD, or to test an implementation that returns the East_Asian_Width property, parse the following relevant lines from PropertyValueAliases.txt and produce a regular expression that concatenates each of the short and long property alias values.

# East_Asian_Width (ea)

ea ; A         ; Ambiguous
ea ; F         ; Fullwidth
ea ; H         ; Halfwidth
ea ; N         ; Neutral
ea ; Na        ; Narrow
ea ; W         ; Wide

The resulting regular expression would then be:


For each Unicode binary character property, the regular expression can be precomputed simply as:


The Catalog properties, Age, Block, and Script, are another type of enumerated character property. All possible values of those properties for any given version of the Unicode Standard are listed in PropertyValueAliases.txt, so a validating regular expression for a Catalog property for that given version of the UCD can be generated by concatenating values, as for the other enumerated properties.

5.11.2 Combining_Character_Class Property

The Combining_Character_Class (ccc) property is a hybrid type. The possible values defined for it in UnicodeData.txt range from 0 to 255 and are numeric values. However, Combining_Character_Class also has symbolic aliases defined for those particular values that are in actual use; those symbolic aliases are listed in PropertyValueAliases.txt. To produce a validating regular expression for Combining_Character_Class, concatenate together the symbolic aliases from PropertyValueAliases.txt, and then add the numeric range 0..255.

5.11.3 Unihan Properties

The validating regular expressions for each property tag defined in the Unihan database are described in detail in [UAX38].

5.11.4 Other Properties

Regular expressions to validate String and Miscellaneous properties in the UCD are provided in Table 21. Although Catalog properties may use strict tests, as described in Section 5.11.1 Enumerated and Binary Properties, generic patterns for Age, Block, and Script are also provided in Table 21.

To simplify the presentation of these expressions, commonly occurring subexpressions are first abstracted out as variables defined in Table 20.

Table 20. Common Subexpressions for Validation

Variable Value
$positiveDecimal [0-9]+\.[0-9]+
$decimal -?$positiveDecimal
$optionalDecimal -?[0-9]+(\.[0-9]+)?
$name [a-zA-Z0-9]+([_-\ ][a-zA-Z0-9]+)*
$codePoint (10|[A-F0-9])?[A-F0-9]{4}

The regular expressions listed in Table 21 cover all the straightforward cases for other property values. For properties involving somewhat more irregular values, such as Age, ISO_Comment, and Unicode_1_Name, details for validation can be found in [UAX42].

Table 21. Regular Expressions for Other Property Values

Abbr Name Regex for Allowable Values
nv Numeric_Value /$decimal/ Field 2
/$optionalDecimal/ Field 3
blk Block /$name/
sc Script
dm Decomposition_Mapping /$codePoint+/
cf Case_Folding /$codePoint+/
lc Lowercase_Mapping
tc Titlecase_Mapping
uc Uppercase_Mapping
sfc Simple_Case_Folding /$codePoint/
slc Simple_Lowercase_Mapping
stc Simple_Titlecase_Mapping
suc Simple_Uppercase_Mapping
bmg Bidi_Mirroring_Glyph /$codePoint/
na Name /$name/

5.12 Deprecation

In the Unicode Standard, the term deprecation is used somewhat differently than it is in some other standards. Deprecation is used to mean that a character or other feature is strongly discouraged from use. This should not, however, be taken as indicating that anything has been removed from the standard, nor that anything is planned for removal from the standard. Any such change is constrained by the Unicode Consortium Stability Policies [Stability].

For the Unicode Character Database, there are two important types of deprecation to be noted. First, an encoded character may be deprecated. Second, a character property may be deprecated.

When an encoded character is strongly discouraged from use, it is given the property value Deprecated=True. The Deprecated property is a binary property defined specifically to carry this information about Unicode characters. Very few characters are ever formally deprecated this way; it is not enough that a character be uncommon, obsolete, disliked, or not preferred. Only those few characters which have been determined by the UTC to have serious architectural defects or which have been determined to cause significant implementation problems are ever deprecated. Even in the most severe cases, such as the deprecated format control characters (U+206A..U+206F), an encoded character is never removed from the standard. Furthermore, although deprecated characters are strongly discouraged from use, and should be avoided in favor of other, more appropriate mechanisms, they may occur in data. Conformant implementations of Unicode processes such a Unicode normalization must handle even deprecated characters correctly.

In the Unicode Character Database, a character property may also become strongly discouraged—usually because it no longer serves the purpose it was originally defined for. In such cases, the property is labelled "deprecated" in the Table 9, Property Table. For example, see the Grapheme_Link property.

6 Test Files

The UCD contains a number of test data files. Those provide data in standard formats which can be used to test implementations of Unicode algorithms. The test data files distributed with this version of the UCD are listed in Table 22.

Table 22. Unicode Algorithm Test Data Files

File Name Specification Status Unicode Algorithm
BidiTest.txt [UAX9] N Unicode Bidirectional Algorithm
NormalizationTest.txt [UAX15] N Unicode Normalization Algorithm
LineBreakTest.txt [UAX14] N Unicode Line Breaking Algorithm
GraphemeBreakTest.txt [UAX29] N Grapheme Cluster Boundary Determination
WordBreakTest.txt [UAX29] N Word Boundary Determination
SentenceBreakTest.txt [UAX29] N Sentence Boundary Determination

The normative status of these test files reflects their use to determine the correctness of implementations claiming conformance to the respective algorithms listed in the table. There is no requirement that any particular Unicode implementation also implement the Unicode Line Breaking Algorithm, for example, but if it implements that algorithm correctly, it should be able to replicate the test case results specified in the data entries in LineBreakTest.txt.

6.1 NormalizationTest.txt

This file contains data which can be used to test an implementation of the Unicode Normalization Algorithm. (See [UAX15].)

The data file has a Unicode string in the first field (which may consist of just a single code point). The next four fields then specify the expected output results of converting that string to Unicode Normalization Forms NFC, NFD, NFKC, and NFKD, respectively. There are many tricky edge cases included in the input data, to ensure that implementations have correctly implemented some of the more complex subtleties of the Unicode Normalization Algorithm.

The header section of NormalizationTest.txt provides additional information regarding the normalization invariant relations that any conformant implementation should be able to replicate.

The Unicode Normalization Algorithm is not tailorable. Conformant implementations should be expected to produce results as specified in NormalizationTest.txt and should not deviate from those results.

6.2 Segmentation Test Files and Documentation

LineBreakTest.txt, located in the auxiliary directory of the UCD, contains data which can be used to test an implementation of the Unicode Line Breaking Algorithm. (See [UAX14].) The header of that file specifies the data format and the use of the test data to specify line break opportunities. Note that non-ASCII characters are used in this test data as field delimiters.

There is an associated documentation file, LineBreakTest.html, which displays the results of the Line Breaking Algorithm in an interactive chart form, with a documented listing of the rules.

The Unicode text segmentation test data files are also located in the auxiliary directory of the UCD. They contain data which can be used to test an implementation of the segmentation algorithms specified in [UAX29]. The headers of those file specify the data format and the use of the test data to specify text segmentation opportunities. Note that non-ASCII characters are used in this test data as field delimiters.

There are also associated documentation files, which display the results of the segmentation algorithms in an interactive chart form, with a documented listing of the rules:

Unlike the Unicode Normalization Algorithm, the Unicode Line Breaking Algorithm and the various text segmentation algorithms are tailorable, and there is every expectation that implementations will tailor these algorithms to produce results as needed. The test data files only test the default behavior of the algorithms. Testing of tailored implementations will need to modify and/or extend the test cases as appropriate to match any documented tailoring.

6.3 BidiTest.txt

This file contains data which can be used to test an implementation of the Unicode Bidirectional Algorithm. (See [UAX9].)

The data in BidiTest.txt is intended to exhaustively test all possible combinations of Bidi_Class values for strings of length four or less. To allow for the resulting very large number of test cases, the data file has a somewhat complicated format which is described in the header. Fundamentally, for each input string and for each possible input paragraph level, the test data specifies the resulting bidi levels and expected reordering.

The Unicode Bidirectional Algorithm is tailorable within certain limits. Conformant implementations with no tailoring are expected to produce the results as specified in BidiTest.txt and should not deviate from those results. Tailored implementations can also use the data in BidiTest.txt to test for overall conformance to the algorithm by changing the assignment of properties to characters to reflect the details of their tailoring.

7 UCD Change History

This section summarizes the recent changes to the UCD—including its documentation files—and is organized by Unicode versions. The summary includes changes extending all the way back to Unicode 2.0.0, taken from the obsoleted UCD.html documentation file, which predates the creation of this annex. The intent is for this first consolidated version of the annex to preserve that complete prior history from UCD.html. Subsequent versions of the annex will provide only an abbreviated UCD change history section containing only the delta change information from each preceding version.

Starting from Unicode 4.0.1, References in the change history are often made to a Public Review Issue (PRI). See http://www.unicode.org/review/resolved-pri.html for more information about each of those cases.

Changes documented prior to Unicode 4.0 only covered UnicodeData.txt. From Unicode 4.0 onward, the documentation of changes includes modifications of other files as well.

Unicode 6.0.0

Changes in specific files:

Appropriate data files were updated to include the 2,088 new characters added in Unicode 6.0. Two new provisional properties were added. Six older derived properties were deprecated.

Unicode 5.2.0


The documentation file UCD.html was obsoleted. The main documentation for the UCD is now contained in [UAX44]. Documentation specifically for the Unihan data files can be found in [UAX38]

Changes in specific files:

Appropriate data files were updated to include the 6,648 new characters added in Unicode 5.2. Nine new properties were added.


Mark Davis and Ken Whistler are the authors of the initial version and have added to and maintained the text of this annex. Julie Allen and Asmus Freytag provided editorial suggestions for improvement of the text. Over the years, many members of the UTC have participated in the review of the UCD and its documentation.


For references for this annex, see Unicode Standard Annex #41, “Common References for Unicode Standard Annexes.”


For details of the change history, see the online copy of this annex at http://www.unicode.org/reports/tr44/.

The following summarizes modifications from previous revisions of this annex.

Revision 5 [KW]

Revision 4 [KW]

  • Reissued for Unicode 5.2.0.
  • Completely reorganized and rewritten, to include all the content from the obsoleted UCD.html.
  • Added Section 5.10 re deprecation.
  • Added subsection in Section 4.2 re line termination conventions.
  • Added Contributory as a formal status and updated the Property Table accordingly.
  • Added note in Section 5.3.1 to indicate that contributory properties are neither normative nor informative.
  • Updated documentation for default values.
  • Cleaned up description of numeric properties.
  • Tweaked the description of NamesList.html.
  • Miscellaneous minor point edits.
  • Updated summary statement of the document.
  • Centered tables.
  • Added anchors and numbers to tables and adjusted text referencing tables accordingly.
  • Added clarifications about exceptional format issues for Unihan data files.
  • Updated references to Section 4.8, Name—Normative for derived names and for code point labels.
  • Added mention of property aliases from Unihan data files to Section 5.6.1.
  • Added documentation for new derived properties: Cased, Case_Ignorable, Changes_When_Lowercased, Changes_When_Uppercased, Changes_When_Titlecased, Changes_When_Casefolded, Changes_When_Casemapped, NFKC_Casefold, and Changes_When_NFKC_Casefolded.
  • Added strong pointers to Section 3.5 and Chapter 4 of [Unicode] in the Introduction.
  • Added new Section 2.3.1, Changes to Properties Between Releases.
  • Updated default values for East_Asian_Width.
  • Clarified the applicability of comments in cases where properties have multiple default values.
  • Restructured Section 5.1 documentation of columns in the property table, for better text flow.
  • Reordered entries for DerivedCoreProperties.txt in the property table, for clarity.
  • Added documentation of new test file: BidiTest.txt.
  • Updated terminology related to the Unihan Database.
  • Added documentation for the new data file, CJKRadicals.txt.
  • Added Attached_Above for ccc=214 in Table 13.
  • Complete revision of Validation section and associated tables.
  • Minor revision of text in Section 4.1.5, File Directory Differences for Early Releases.
  • Added a cautionary note about the use of the Age property in regular expressions.
  • Added sections explaining obsolete, deprecated, and stabilized properties, and clearly identified existing such properties in the property table.

Revision 3 being a proposed update, only changes between versions 4 and 2 are noted here.

Revision 2

  • Initial approved version for Unicode 5.1.0.

Revision 1

  • Initial draft.