ISO/IEC 10646:2020

Overview

ISO/IEC 10646:2020 - Information technology - Universal coded character set (UCS) defines the architecture and coded character repertoire for global text representation. The standard specifies the UCS codespace, named graphic and format characters across multiple planes (Basic Multilingual Plane - BMP; Supplementary Multilingual Plane - SMP; Supplementary Ideographic Plane - SIP; Tertiary Ideographic Plane - TIP; Supplementary Special-purpose Plane - SSP), and the mechanisms used to encode those characters in software and systems.

Keywords: ISO/IEC 10646, Universal Coded Character Set, UCS, UTF-8, UTF-16, UTF-32, character encoding, Unicode collections, BMP, SMP

Key technical topics and requirements

• Architecture and codespace: Defines structure, terminology, types of code points, and naming conventions for characters and control functions.
• Assigned planes and character repertoires: Specifies BMP, SMP, SIP, TIP and SSP and the set of graphic characters used for world languages and scripts.
• Character naming and code charts: Standardized character names, short identifiers (UIDs), and published code charts and name lists.
• Control and private-use characters: Coded representations for control characters and private use areas.
• Encoding forms and schemes:
  • Encoding forms: UTF-8, UTF-16, UTF-32
  • Encoding schemes: UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32, UTF-32BE, UTF-32LE
• Normalization and combining behavior: Rules for combining characters, canonical ordering, normalization forms and grapheme handling.
• Bidirectional text and presentation: Mirroring rules and directionality for mixed-script text (e.g., Arabic/Hebrew).
• Variation selectors and sequences: Support for standardized variation sequences and presentation variants.
• Revision and management: Procedures for updating the UCS and managing future additions (including source references for CJK, Tangut, Nüshu).
• Conformance and subsets: Rules for conformance, limited/selected subsets, and subset identification.

Note: Determination of suitability of these characters for programming language identifiers is outside this document (see Annex U for external references).

Practical applications and users

ISO/IEC 10646 is essential for:

• Software developers implementing text processing, file formats, APIs and libraries
• Operating system and platform vendors ensuring consistent text handling
• Font designers and typographers mapping glyphs to code points
• Localization and internationalization engineers handling multilingual data
• Database architects and data interchange systems ensuring interoperability
• Standards bodies and protocol designers referencing a canonical coded character set

Adopting ISO/IEC 10646 ensures reliable storage, interchange, rendering and processing of global text across web, mobile, enterprise and embedded systems.

Related standards

• Unicode Consortium materials and Unicode character database (ISO/IEC 10646 references and aligns with Unicode collections)
• Encoding specifications: UTF-8, UTF-16 and UTF-32 transformation formats (normative in the standard)

For implementation, consult the code charts, Annexes (UTF-8/UTF-16 transformation formats), and conformance clauses in ISO/IEC 10646:2020.