https://twitter.com/ken_lunde/status/1264037362058706949
ふむ・・・。A Tale of Three (OpenType) Featuresにも書いてあるのか。
sideways typesetting
Typographic character units typeset as a run rotated 90° clockwise from their upright orientation, using horizontal metrics and composition, and vertical typesetting features are not used. However, if the font has features meant to be enabled for sideways text that is typeset in vertical lines (e.g. to adjust brush stroke angles or alignment), those features are used. (An example of such a feature would be the proposed vrtr OpenType font feature.)
なんて英語で読んでられないし、CSS Writing Modes Level 3 （日本語訳）を読む。要は縦専用の字形に置換してやればいいのか・・・？
