[MPEG-OTSPEC] Is it valid to use a GSUB sequence with a leading ZWJ character please?

[John Hudson]

On 14102022 2:51 pm, David Lemon wrote:
> William, I'm curious: Why are you leading with a [ZWJ] instead of 
> placing it between the to-be-ligated characters?

A ligature lookup is one possible implementation of a graphical 
ligation. My understanding of what William is doing is akin to handling 
the graphical ligation using contextual ligating forms—i.e. two or more 
glyphs that when employed together appear to form a ligated shape—rather 
than a single ligature glyph. In this case, instead of the substitution 
being contextual, he is using ZWJ as part of the input to affect the 
ligating form, which in this case is an overlay combining mark glyph.

I should emphasise that I mostly ignore everything to do with emoji 
encoding, so I am not sure whether what William is trying to do is 
kosher Unicode. I do know that when I suggested the idea of a formatting 
control character that converts the immediately following arbitrary 
character into a combining mark—so as to avoid having to propose new 
combining mark characters to represent things like superscribed letters 
in manuscripts—I was told by UTC members that was a non-starter.

JH

-- 

John Hudson
Tiro Typeworks Ltd    www.tiro.com

Tiro Typeworks is physically located on islands
in the Salish Sea, on the traditional territory
of the Snuneymuxw and Penelakut First Nations.

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