CJK Unified Ideographs Extension I

Unlike most other sets of CJK unified ideographs, Extension I was not prepared and submitted by the Ideographic Research Group (IRG).

GB 18030 is a mandatory national standard of the People's Republic of China (PRC). It defines a Unicode Transformation Format which retains compatibility with existing data in the earlier GBK and EUC-CN character encodings, and specifies particular Unicode characters which devices sold in China must support.[3] Its 2022 edition, GB 18030-2022, changed a number of required characters to map to standard Unicode code points, rather than to private use area code points.

In late 2022, the PRC made a draft of a further amendment to be made to GB 18030 available for public consultation. This draft would have placed 897 new sinographic characters in Plane 10 (hexadecimal: 0A), a yet-untitled astral Unicode plane.[4] This was motivated by a "strong need of citizen real-name certification in China".[5] Since it would impact ISO/IEC 10646 (the Universal Coded Character Set, the ISO standard synchronised with Unicode), the draft was circulated in ISO/IEC JTC 1/SC 2, the ISO subcommittee responsible for ISO 10646. The Chinese national body maintained that "ISO/IEC 10646 do not specify the purpose of the 0A plane", which ISO 10646 denotes as "reserved for future standardization", and that this use was therefore "not inappropriate".[4]

However, since the intent of ISO 10646 was for Plane 10 to be reserved for future allocation by ISO 10646 and Unicode via their usual ballot process, not for it to be allocated unilaterally by national standards bodies, this proposed move was criticised by experts and other national bodies as one which would "destabilize the synchronization" between GB 18030 and ISO/IEC 10646 (and thus Unicode), and which would make it impossible to conform to both with a single implementation,[4] effectively forking Unicode.

As an alternative, the repertoire (eventually reduced to 622 characters after expert review) was fast-tracked into Unicode version 15.1 in the CJK Unified Ideographs Extension I block.[4] The CJK Unified Ideographs Extension D block was cited as a precedent, since it comprised a repertoire of urgently needed characters (UNCs) from IRG member bodies, whereas the IRG working-set initially slated to become Extension D would instead become Extension E.[6] For compactness, the block was allocated to the available space in the Supplementary Ideographic Plane after CJK Unified Ideographs Extension F, as opposed to on the Tertiary Ideographic Plane after CJK Unified Ideographs Extension H; this means that the CJK extension blocks are no longer in alphabetical order by extension letter.[7] Following this, the draft GB 18030 amendment was modified to use the Extension I code points.[5]

The Extension I characters make up the "GIDC23" Unihan source,[8] defined as sourced from the "ID system of the Ministry of Public Security of China, 2023".[9]

The following Unicode-related documents record the purpose and process of defining specific characters in the CJK Unified Ideographs Extension I block:

• Lunde, Ken (2023-07-15). "The First Amendment". This article details how the CJK Unified Ideographs Extension I block became standardized, and its relationship with two drafts of the GB 18030-2022 amendment.