RE: [OpenType] Further thoughts on ZWJ ligation

From: John Hudson (
Date: Fri Jul 19 2002 - 14:41:52 EDT

At 11:24 AM 19-07-02, Paul Nelson wrote:

>If you look at OT font specifications on the Microsoft web site you see
>that we recommend these glyphs be in font and provide a suggested shape
>for when they are glyphed. Show Symbols in Microsoft applications will
>have these rendered. Thus, a user can see when the control characters
>are used. Kind of nice to have when editing text.

Yes, but the implication of using ZWJ for, e.g. Latin ligatures, is that
the ligature substitutions will not happen when the control characters are
not displayed (i.e. when Show Symbols is not turned on), but when such
control characters are displayed, the ZWJ sequences will be replaced by
ligatures -- ironically *not* showing the symbol -- and the text may be
littered with other, unwanted control characters, including a visual
representation of ZWNJ if it occurs.

So, you either have ZWJ invisible and not doing anything, or you have ZWJ
nominally visible but actually invisible because it is involved in a
ligature substitution lookup, the latter also requiring that every other
control character in the text is visible. This is what I mean when I say
that the ligature behaviour added to ZWJ is incompatible with existing
implementations of ZWJ as a control character for discretionary complex
script shaping.

John Hudson

Tiro Typeworks
Vancouver, BC

Language must belong to the Other -- to my linguistic community
as a whole -- before it can belong to me, so that the self comes to its
unique articulation in a medium which is always at some level
indifferent to it. - Terry Eagleton

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