ZWJ as a Ligature Suppressor

Andrew Glass (WINDOWS) Andrew.Glass at
Mon Aug 10 12:58:24 CDT 2015

Hi Richard,

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.
Program Manager
Shell Text Input Group | Windows | Microsoft

-----Original Message-----
From: Unicode [mailto:unicode-bounces at] On Behalf Of Richard Wordingham
Sent: Sunday, August 9, 2015 3:58 AM
To: unicode at
Subject: ZWJ as a Ligature Suppressor

According to the text just after TUS 7.0.0 Figure 23-3 (, 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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