Han Unification

What is Han Unification?

Han Unification, formally known as CJK Unified Ideographs, is the process by which the Unicode Consortium assigned single code points to Chinese, Japanese, and Korean (CJK) characters that share the same historical origin and abstract meaning, even though their printed forms can differ significantly across regions. The result is the CJK Unified Ideographs block (U+4E00–U+9FFF) and several extension blocks (Extension A through Extension I), together containing over 98,000 ideographs.

The core principle is straightforward: if two characters in Chinese, Japanese, and Korean descend from the same historical Chinese character and carry the same semantic meaning, they are unified into a single code point. A reader in Beijing, Tokyo, or Seoul would recognize the same abstract concept, even if their local typographic tradition renders the strokes slightly differently.

The Controversy: Source Separation vs. Unification

Han Unification has been one of the most debated decisions in Unicode history. Critics, especially from Japan, argue that the policy conflates characters that Japanese users consider distinct. The classic example is the character for "grass radical" — in Japanese printing it traditionally appears as a three-stroke form, while in Chinese it appears as a four-stroke form. Unifying them onto one code point means selecting which glyph to display falls entirely to the font, not to the text itself.

Proponents argue that encoding every regional glyph variant as a separate code point would multiply the size of the character set many times over and that Han Unification mirrors how Latin-script readers accept that the same letter looks different in different typefaces.

The controversy gave rise to formal mechanisms to handle legitimate distinctions:

• IRG (Ideographic Rapporteur Group): The ISO/IEC working group that advises Unicode on CJK matters, comprising national representatives from China, Taiwan, Japan, Korea, Vietnam, and others. The IRG reviews proposals for new ideographs, verifies source references, and mediates unification disputes.
• IVD (Ideographic Variation Database): A Unicode-registered database of Variation Sequences that allow text to specify which regional glyph variant is intended. A base character followed by a Variation Selector (U+E0100–U+E01EF for ideographic variation) unambiguously selects a specific glyph. For example, the sequence U+82F1 U+E0101 requests a specific Japanese form of the character for "England/hero" that differs from the default Chinese form.

Technical Implications

When working with CJK text programmatically, Han Unification has several practical consequences:

• Font selection is semantically significant: A document using Chinese characters must use a Chinese-locale font to render correctly. The same bytes rendered with a Japanese font may display noticeably different glyphs.
• Locale metadata matters: The lang attribute in HTML (lang="ja" vs. lang="zh") tells the browser which font to prefer, directly affecting how unified ideographs appear.
• Variation sequences must be preserved: Text processing pipelines that strip non-printing characters can inadvertently destroy intentional glyph disambiguation encoded via variation selectors.

Extension Blocks

Unicode has added CJK extensions as more historical and regional characters were identified:

Quick Facts