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w3c / jlreq

Text Layout Requirements for Japanese
https://w3c.github.io/jlreq/
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Use U+22EF MIDLINE HORIZONTAL ELLIPSIS for ellipses? #327

Open xfq opened 2 years ago

xfq commented 2 years ago

Chapter 6.2, pages 276-277 of v14 of the Unicode Standard suggests using ⋯ U+22EF MIDLINE HORIZONTAL ELLIPSIS instead of … U+2026 HORIZONTAL ELLIPSIS for CJK:

In East Asian typographic traditions, particularly in Japan, an ellipsis is raised to the center line of text. When an ellipsis is represented by U+2026 HORIZONTAL ELLIPSIS or by sequences of full stops, this effect requires specialized rendering support. In practice, it is relatively common for authors of East Asian text to substitute U+22EF MIDLINE HORIZONTAL ELLIPSIS for this. Because the midline ellipsis is a mathematical symbol, intended to represent column elision in matrix notation, it is typically used with layout on a mathematical center line. With appropriate font design to harmonize with East Asian typography, this midline ellipsis can produce the desired appearance without having to support contextual shifting of the baseline for U+2026 HORIZONTAL ELLIPSIS.

U+22EE VERTICAL ELLIPSIS and U+22EF MIDLINE HORIZONTAL ELLIPSIS are part of a set of special ellipsis characters used for row or column elision in matrix notation. Although their primary use is for a mathematical context, U+22EF MIDLINE HORIZONTAL ELLIPSIS has also become popular for the midline ellipsis in East Asian typography. When U+22EF is used this way, an East Asian font will typically contain a rotated glyph variant for use in vertical text layout. If an appropriate mechanism for glyph variant substitution (such as the “vert” GSUB feature in the Open Font Format) in vertically rendered text is not available, U+FE19 presentation form for vertical horizontal ellipsis is the preferred character substitution to represent a vertical ellipsis, instead of the mathematical U+22EE VERTICAL ELLIPSIS.

Should we consider adding the midline ellipsis to the list of unbreakable character sequences (分割禁止)? I'm not sure if this character is in the JIS standard, tho.

himorin commented 2 years ago

In current JLreq NOTE whole document is based on JIS codepoints, and 0x2144 (ISO-2022-JP) for horizontal ellipses is mapped to U+2026 as in Conversion table at unicode.org, but there is no mapping to U+22EF. JL-TF has been discussing to upgrade character class categories based on Unicode, which is supposed to be used as a base for upcoming document (temporary called as JDLreq - Japanese Digital Layout requirements), and Inseparable line breaking group in unicode contains both U+2026 and U+22EF.

I believe it is not worth working (just) to update existing JLReq document with Unicode based character handling. Of course, I agree that JL-TF should release a solid text for character class categories based on Unicode and its attributes.