text-transform: full-width transforms all the characters in the text to be “full-width” — to match the width of characters defined in an East Asian script like Chinese, Japanese, or Korean (CJK). It’s ...

It would have turned something like しゃ into しや. The two are not equivalent, (the first is pronounced “sha”, the second “shiya”), but at very small font sizes inside ruby text, this substitution is ...