CJK Unified Ideographs Extension B is a Unicode block containing rare and historic CJK ideographs for Chinese, Japanese, Korean, and Vietnamese submitted to the Ideographic Research Group between 1998 and 2000, plus seven gongche characters for kunqu added in Unicode 13.0, and two characters for the Macao Supplementary Character Set added in Unicode 14.0.
Variation selector sequences
The block has dozens of variation sequences defined for standardized variants. It also has thousands of ideographic variation sequences registered in the Unicode Ideographic Variation Database (IVD). These sequences specify the desired glyph variant for a given Unicode character.
Development process
SuperCJK
The repertoire of Extension B was developed by the Ideographic Rapporteur Group in successive revisions of a document named "SuperCJK". This lists all characters included at the time in the Unified Repertoire and Ordering, in Extension A and in the draft Extension B, ordered by radical and residual stroke count. Each character was included with up to four glyph bitmaps, and references to character sources including the Kangxi Dictionary, the Hanyu Da Zidian, and various national character set standards.
"UCS2003" glyphs
Extension B was the only CJK Unified Ideographs Extension block with a UCS2003 source identifier. Since Extension B contained too many characters, the original code charts were produced with a single glyph for all regions. The glyphs were designed by Beijing Zhongyi Electronic Ltd. After the introduction of multi-column code charts on Unicode 5.2, the original glyphs were retained under the UCS2003 source identifier; they were then removed in Unicode 14.0, being redundant as well as misleading. The glyphs are packaged in the "SimSun-ExtB" font distributed with the Simplified Chinese versions of Windows, and do not adhere to the glyphs for the Mainland China region.
Known issues
Size Extension B contains 42720 (initially 42711) characters, more than double the 20992 included in the Unified Repertoire and Ordering, and far more than any other CJK extension block (the second-largest of which, as of Unicode 17.0, is CJK Unified Ideographs Extension F, with 7473 characters). This also makes it the only block, besides Private Use Areas, to occupy more than half of the 65534 allocatable codepoints in a Unicode plane.
Owing to its size, a number of mistakes have been discovered in the original version of Extension B since it was encoded. To facilitate better review of proposed characters, the working set size for subsequent CJK extension blocks has been kept much smaller; for example, the Ideographic Research Group currently requests that its member bodies should usually submit no more than 2500 characters each, so as to keep the size of the working set below 10000 characters if possible.
Unifiable variants and exact duplicates in Extension B In CJK Unified Ideographs Extension B, hundreds of glyph variants were encoded. In addition to the deliberate encoding of close glyph variants, seven exact duplicates (where the same character has inadvertently been encoded twice) and two semi-duplicates (where the CJK-B character represents a de facto disunification of two glyph forms unified in the corresponding BMP character) were encoded by mistake:
Included in Extension B twice
U+204F2 𠓲 = U+23515 𣔕 : same glyph shapes, but ordered under different radicals U+21018 𡀘 = U+2103C 𡀼 : same glyph shapes U+249BC 𤦼 = U+249E9 𤧩 : same glyph shapes U+24BD2 𤯒 = U+2A415 𪐕 : same glyph shapes, but ordered under different radicals U+26842 𦡂 = U+26866 𦡦 : same glyph shapes
Unconditional exact duplicate of Basic Multilingual Plane character
U+3DB7 㶷 = U+2420E 𤈎 : same glyph shapes U+FA23 﨣 = U+27EAF 𧺯 : same glyph shapes (U+FA23 﨣 is a unified CJK ideograph, despite its name "CJK COMPATIBILITY IDEOGRAPH-FA23.")
Exact duplicate of Basic Multilingual Plane character in some localised fonts
U+34A8 㒨 = U+20457 𠑗 : U+20457 is the same as the China-source glyph for U+34A8, but it is significantly different from the Taiwan-source glyph for U+34A8 U+8641 虁 = U+27144 𧅄 : U+27144 is the same as the Korean-source glyph for U+8641, but it is significantly different from the mainland Chinese-, Taiwan- and Japan-source glyphs for U+8641
Block
History The following Unicode-related documents record the purpose and process of defining specific characters in the CJK Unified Ideographs Extension B block:
Version Count L2 ID WG2 ID IRG ID Document 3.1 U+20000..2A6D6 42,711 N2109 N674 N2105 N675 N2144 N713R N2103 rtf) doc) N2298 N758 doc) N2347 N785 doc) N787 N2427 N2448 N924 N2518 N2695 N1026 N2774R N1064 N2830 doc) N3285 N1406 doc) N4111 N4103 N4621 doc) N2202 N4974 N2301 N4987 N4988 N2336 N5016 N2349 doc) N5086 N2379 N5068 N5107 N5083 N2391 N5082 N2508 N2512R N2520 N2580R N2556R2 N2588R N2609 N2642 N2651 N2779R2 13.0 U+2A6D7..2A6DD 7 N2296 N2299 N4967 doc) N5122 N5106 14.0 U+2A6DE..2A6DF 2 N5140 N2437
References