[MPEG-OTSPEC] 'curs' feature: required?

[Peter Constable]

Is the 'curs' feature considered a required feature for Arabic or other cursively-connecting scripts?

I would have expected it's required. It's clear the intent is for triggering cursive attachment positioning (GPOS type 3), and Microsoft's Arabic implementation spec<https://docs.microsoft.com/en-us/typography/script-development/arabic> lists it among features to be applied in GPOS processing. But the description in the OTL feature registry<https://docs.microsoft.com/en-us/typography/opentype/spec/features_ae#tag-curs> is worded in a way that makes it sound optional, at the user's discretion:

"UI suggestion: This feature could be made active or inactive by default, at the user's preference."



Peter
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