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

[William_J_G Overington]

Hello John

Thank you for your helpful reply.

Best regards,

William Overington

Saturday 15 October 2022



------ Original Message ------
From: "John Hudson" <john at tiro.ca>
To: mpeg-otspec at lists.aau.at
Sent: Friday, 2022 Oct 14 At 23:33
Subject: Re: [MPEG-OTSPEC] Is it valid to use a GSUB sequence with a 
leading ZWJ character please?

I don’t see any reason why beginning a       GSUB input sequence with 
ZWJ should not be valid, but that isn’t       the same thing as implying 
that you might not run into problems in       particular OTL 
implementations.



ZWJ and other formatting control       characters with representative 
glyphs — properly only displayed in       editing environments, not in 
text presentation — should be       available to GSUB, but then 
suppressed from the resulting glyph       string for GPOS and display 
purposes. That behaviour is mostly       reliable in complex script 
shaping engines, but it is possible       that the path emoji take in 
some environments may run into       unexpected issues with some part of 
this procedure.




JH


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