Z-variant

In Unicode, two glyphs are said to be Z-variants (often spelled zVariants) if they share the same etymology but have slightly different appearances and different Unicode code points. For example, the Unicode characters U+8AAA 說 and U+8AAC 説 are Z-variants. The notion of Z-variance is only applicable to the “CJKV scripts”—Chinese, Japanese, Korean and Vietnamese—and is a subtopic of Han unification.

Differences on the Z-axis

The Unicode philosophy of code point allocation for CJK languages is organized along three “axes.” The X-axis represents differences in semantics; for example, the Latin capital A (U+0041 A) and the Greek capital alpha (U+0391 Α) are represented by two distinct code points in Unicode, and might be termed “X-variants” (though this term is not common). The Y-axis represents significant differences in appearance though not in semantics; for example, the traditional Chinese character māo “cat” (U+8C93 貓) and the simplified Chinese character (U+732B 猫) are Y-variants.[1]

The Z-axis represents minor typographical differences. For example, the Chinese characters (U+838A 莊) and (U+8358 荘) are Z-variants, as are (U+8AAA 說) and (U+8AAC 説). The glossary at Unicode.org[1] defines “Z-variant” as “Two CJK unified ideographs with identical semantics and unifiable shapes,” where “unifiable” is taken in the sense of Han unification.

Thus, were Han unification perfectly successful, Z-variants would not exist. They exist in Unicode because it was deemed useful to be able to “round-trip” documents between Unicode and other CJK encodings such as Big5 and CCCII. For example, the character 莊 has CCCII encoding 21552D, while its Z-variant 荘 has CCCII encoding 2D552D. Therefore, these two variants were given distinct Unicode code points, so that converting a CCCII document to Unicode and back would be a lossless operation.

Confusion

There is some confusion over the exact definition of “Z-variant.” For example, in an Internet draft (of RFC 3743) dated 2002,[2] one finds bù “no” (U+4E0D 不) and (U+F967 不) described as “font variants,” the term “Z-variant” being apparently reserved for interlanguage pairs such as the Mandarin Chinese tù “rabbit” (U+5154 兔) and the Japanese to “rabbit” (U+514E 兎). However, the Unicode Consortium's Unihan database [3] treats both pairs as Z-variants.

gollark: Okay, FINE, here you go.
gollark: Yes, which you have to do to actually spend it.
gollark: Anyway, here is my *alternative* tax policy plotted on the same axes.
gollark: That doesn't seem like a problem? If they only get minimum wage, they... only get minimum wage? Capital gains tax is a thing.
gollark: Tax should clearly be done like this (precise numbers subject to change).

See also

References
  1. "Glossary". www.unicode.org.
  2. Huang, K.; Ko, Y.; Konishi, K.; Qian, H. "Joint Engineering Team (JET) Guidelines for Internationalized Domain Names (IDN) Registration and Administration for Chinese, Japanese, and Korean". tools.ietf.org.
  3. "Unihan Database Lookup". www.unicode.org.
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