WebKit doesn't tailor grapheme cluster rules to take into account full orthographic syllables represented as conjuncts, upright characters in vertical lines of text don't break correctly. See requirements at: https://w3c.github.io/ilreq/#h_vertical_arrangements_of_characters , but add to those the points made in https://w3c.github.io/i18n-drafts/questions/qa-indic-graphemes.en.html Tests & results: When devanagari characters are rendered upright in vertical text, orthographic syllables containing conjuncts are kept together: https://github.com/w3c/text_direction_tests/issues/10 An attempt has been made to keep conjuncts together, but pre-base consonants are rendered alone.
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