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Re: [csswg-drafts] [css-inline-3] Ascent and Descent Metrics in vertical flow (#5381)

From: Nat McCully via GitHub <sysbot+gh@w3.org>
Date: Fri, 14 Aug 2020 00:24:33 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-673773369-1597364672-sysbot+gh@w3.org>
In InDesign, there is the concept of the line's metrics (always single-direction), dictated to be either Latin ascent/descent or CJK embox according to paragraph attributes (CJK composer = embox, other composers = ascent/descent), of the largest run. TCY has internal metrics during composition but those are limited (e.g. different baseline alignments in the horizontal direction are not supported), and the TCY is in the end treated as a single CJK vertical upright glyph with a height and width of 1 em (of the tallest TCY character), on a center vertical baseline, that can bleed outside its typographic boundaries if longer than a few characters (so as not to disturb the line height or leading rhythm).

Mixed script text introduces further complexity, but I still feel strongly that the user needs a way to set paragraphs to use either a CJK embox metrics model or a Latin ascent/descent metrics model as the two cannot be mixed without compromise of behavior and adherence to traditional practice (Japanese or Latin) when dealing with edge cases.

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