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Re: [csswg-drafts] [css-text] Clarify what ligatures are optional (#2644)

From: fantasai via GitHub <sysbot+gh@w3.org>
Date: Tue, 04 Dec 2018 23:01:15 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-444292691-1543964474-sysbot+gh@w3.org>
> I am also interested in which ligatures are "optional".

>From CSS3 Text's perspective, that would be any ligatures which are not required. Per @litherum's https://github.com/w3c/csswg-drafts/issues/2644#issuecomment-422075536 that means anything except `rlig` in OpenType. And maybe there needs to be some special handling for Khmer because of its broken relationship with OpenType ligature tags. It's technically out-of-scope for CSS to define what OpenType considers required, though. I tried to add some clarifications on this point in https://github.com/w3c/csswg-drafts/commit/caf1e4747f2bd906bb9f671af8c463b28b97deda though.

Wrt Fraktur, it seems that using Fraktur changes the definition of “typographic grapheme cluster”, and pages tagged with `de-Latf` should have their segmentation adjusted accordingly. There's hundreds of examples of this type of thing, and it might be nice to have a registry where we collect info on “what's a typographic grapheme cluster” in all the various writing systems and variants thereof, but that's definitely too detailed for the CSS Specification. However the i18nWG is collecting such info in its *REQ reports, and it would be a good idea to have it noted in LatinReq and add corresponding WPT tests. https://www.w3.org/International/layout I can add this one as an example of how segmentation can vary by lang tag, though, since I think I don't have such an example yet in the spec.

Wrt updating the font feature precedence rules to be clearer about the various types of ligatures, your wording changes for rule 4 seem clearly correct to me; I'm not convinced about the others though. Deferring to @litherum and @svgeesus on that.

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Received on Tuesday, 4 December 2018 23:01:18 UTC

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