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[csswg-drafts] [css-inline-3] sTypoAscender / sTypoDescender should not be recommended (#5485)

From: Myles C. Maxfield via GitHub <sysbot+gh@w3.org>
Date: Sat, 29 Aug 2020 04:16:12 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-688454917-1598674571-sysbot+gh@w3.org>
litherum has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-inline-3] sTypoAscender / sTypoDescender should not be recommended ==

> Note: It is recommended that implementations that use OpenType or TrueType fonts use the metrics sTypoAscender and sTypoDescender from the font’s OS/2 table (after scaling to the current element’s font size) to find the ascent metric and descent metric for CSS layout. In the absence of these metrics, the "Ascent" and "Descent" metrics from the HHEA table should be used.

WebKit on macOS and iOS uses Core Text, and Core Text usually uses the metrics from the `hhea` table. (Note, `hhea` [is](https://docs.microsoft.com/en-us/typography/opentype/spec/hhea) lowercase, not uppercase.) The CSS spec should not pretend that using metrics from `hhea` is any worse than using metrics from `OS/2`.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/5485 using your GitHub account

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