CJK Compatibility Ideographs
CJK Compatibility Ideographs is a Unicode block created to contain mostly Han characters that were encoded in multiple locations in other established character encodings, in addition to their CJK Unified Ideographs assignments, in order to retain round-trip compatibility between Unicode and those encodings. However, it also contains 12 unified ideographs sourced from Japanese character sets from IBM.
The block has dozens of ideographic variation sequences registered in the Unicode Ideographic Variation Database.
These sequences specify the desired glyph variant for a given Unicode character.
Character sources
Sources for the original collection of CJK Compatibility Ideographs include:- South Korean KS X 1001
- Taiwanese Big5
- "IBM 32": 32 Japanese characters from IBM
- South Korean KS X 1001
- Japanese JIS X 0213
- Japanese ARIB STD-B24
- North Korean KPS 10721-2000
The "IBM 32" characters
IBM Japanese double-byte EBCDIC includes several kanji which do not exist in, or do not round-trip from, JIS X 0208. These were included as gaiji in extensions to Shift JIS and EUC-JP from IBM, NEC, the Open Software Foundation, and Microsoft. However, they were not used as a source for the original Unified Repertoire and Ordering. Instead, 32 of the IBM extension kanji, those which had not been included in the URO from other sources, were included in the CJK Compatibility Ideographs block in the range U+FA0E-U+FA2D.Of these 32 characters:
- 19 are unifiable with characters in the URO, and are therefore compatibility ideographs in the strict sense.
- 12 are kokuji characters which are actually unified ideographs. In spite of their inclusion in the CJK Compatibility Ideographs block and their algorithmically generated character names beginning with "", they are not duplicates of characters in the original CJK Unified Ideographs block in any respect; 11 of these 12 are completely non-duplicate, while was later unintentionally duplicated in CJK Unified Ideographs Extension B as. They are placed there because they do not have a URO encoding, yet IBM 32 is one of the encodings where duplicate encodings are of concern. All of them are rarely used or are variants of common kanji. They are as follows:
- Uniquely, is intended to be encoded as the kyūjitai form of a kokuji which received a separate encoding for a variant that is straightforwardly the (extended) shinjitai form. The URO only encoded the shinjitai form, and uses its stroke count to place it in this position. It is furthermore one variant of the many variants of the jinmeiyō kanji . U+FA20 was assigned a normalisation to U+8612, even though the 龜 and 亀 components, while both forms of radical 213, are not usually considered unifiable.