CJK（中日韩）

What is CJK?

CJK stands for Chinese, Japanese, and Korean — the three major East Asian languages whose writing systems share a common inventory of logographic characters known as CJK Unified Ideographs. In Unicode, CJK refers specifically to the process of encoding these shared ideographs in a single unified code block rather than encoding separate sets for each language.

The term is sometimes extended to CJKV (adding Vietnamese) since Vietnamese historically used Chữ Nôm, a writing system also based on Chinese ideographs.

The Han Unification Decision

The central and controversial decision in Unicode's CJK handling is Han unification: assigning a single code point to an ideograph that appears in two or more of the CJK writing traditions, even if those traditions render it with slightly different glyph shapes.

For example, the ideograph meaning "country/nation" is: - Chinese: 国 (Simplified) or 國 (Traditional) - Japanese: 国 (Kanji) - Korean: 국 (Hanja, pronounced "guk")

Unicode assigns both Simplified 国 (U+56FD) and Traditional 國 (U+570B) as separate code points because they have distinct shapes. But many other ideographs that differ only in minor glyph details between countries are unified into a single code point, with font selection determining the rendering variant.

CJK Code Blocks in Unicode

Total CJK ideographs across all extensions: over 90,000 as of Unicode 16.0.

Hanzi, Kanji, Hanja — One Code Point

The unification means that U+4E2D (中, "middle/China") is simultaneously: - Chinese: 中 (zhōng) - Japanese: 中 (naka/chū) - Korean: 중 (jung)

Which glyph is rendered depends on the font and language context. A Chinese font renders 中 in the standard Chinese style; a Japanese font renders it in the Japanese kanji style. The Unicode Standard includes a set of source separation rules that determined when two apparently similar ideographs should be unified versus kept separate.

CJK Radicals and Strokes

CJK ideographs are built from components called radicals (部首, bùshǒu). Unicode encodes:

• Kangxi Radicals (U+2F00–U+2FDF): 214 traditional radicals used in Chinese dictionaries
• CJK Radicals Supplement (U+2E80–U+2EFF): Alternative and simplified radical forms
• Stroke order: Not encoded in Unicode; defined by external standards per language

Working with CJK in Code

import unicodedata

char = "中"
print(unicodedata.name(char))           # CJK UNIFIED IDEOGRAPH-4E2D
print(unicodedata.category(char))       # Lo (Letter, other)
print(hex(ord(char)))                   # 0x4e2d

# CJK range check
def is_cjk_unified(char: str) -> bool:
    cp = ord(char)
    return 0x4E00 <= cp <= 0x9FFF  # Core block only

def is_cjk_any(char: str) -> bool:
    cp = ord(char)
    ranges = [
        (0x4E00, 0x9FFF),   # Core
        (0x3400, 0x4DBF),   # Extension A
        (0x20000, 0x2A6DF), # Extension B
        (0x2A700, 0x2CEAF), # Extensions C-F
        (0x30000, 0x3134F), # Extension G
    ]
    return any(start <= cp <= end for start, end in ranges)

print(is_cjk_unified("中"))  # True
print(is_cjk_unified("A"))   # False

The Han Unification Controversy

Han unification remains controversial among East Asian scholars and users. Critics argue: - Unifying characters obscures important cultural and linguistic distinctions - Font selection should not determine meaning or provenance - Japanese and Chinese variants of the "same" ideograph can differ in stroke count and form

Defenders argue: - Most unified characters are genuinely identical in meaning and origin - Localization (font + language tags) correctly handles rendering differences - Encoding all variants separately would require tens of thousands more code points

The Unicode Standard's response: the CJK Compatibility Ideographs block (U+F900–U+FAFF) provides pre-unified code points for round-trip compatibility with East Asian legacy encodings. However, these are compatibility characters — they normalize to the unified forms under NFKC/NFKD.

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