ZWJ as a Ligature Suppressor
Andrew Glass (WINDOWS)
Andrew.Glass at microsoft.com
Mon Aug 10 12:58:24 CDT 2015
To ligate or not to ligate is up to the font designer. Normally, GSUB lookups that perform ligation will be broken by the presence of ZWJ or ZWNJ. If a font designer wishes to ligate in the presence of a ZWJ or ZWNJ then they could choose to include appropriate glyph sequences in their ligation lookups. For example:
glyphA glyphB -> glyphC
glyphA ZWJ glyphB -> glyphC
Andrew Glass Ph.D.
Shell Text Input Group | Windows | Microsoft
From: Unicode [mailto:unicode-bounces at unicode.org] On Behalf Of Richard Wordingham
Sent: Sunday, August 9, 2015 3:58 AM
To: unicode at unicode.org
Subject: ZWJ as a Ligature Suppressor
According to the text just after TUS 7.0.0 Figure 23-3 (http://www.unicode.org/versions/Unicode7.0.0/ch23.pdf#G25237), ZWJ suppresses ligatures in Arabic script. Does this rule apply to other normally cursive joined scripts, e.g. Syriac and Mongolian?
Am I right in thinking that for an OpenType font for other scripts, the font writer must take precautions to prevent ZWJ accidentally suppressing ligatures that would be better suppressed by ZWNJ or <ZWJ ZWNJ ZWJ>?
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