I recently filed a bug report on the XeTeX repo about the kerning of sub- and superscripts in OpenType fonts: https://sourceforge.net/p/xetex/bugs/175/ luaTeX's find_math_kern() has many of the same flaws. Cheers, David. P.S. I don't think the related bug https://sourceforge.net/p/xetex/bugs/173/ is relevant here because luaTeX's analyze_script() already does essentially the same thing (I haven't compared the two implementations in detail). In fact, analyze_script() does more, since it also handles the sub_box case. ________________________________ David Jones Publications Technical Specialist +1 401.455.4000 (t) [https://www.ams.org/images/ams-logo-270x72.jpg] 201 Charles Street | Providence, RI 02904-2213 USA [https://www.ams.org/images/url.jpg]https://www.ams.org | [https://www.ams.org/images/Facebook-icon.jpg] https://www.facebook.com/amermathsoc [https://www.ams.org/images/instagram-icon.jpg] https://www.instagram.com/amermathsoc/ [https://www.ams.org/images/linkedin-icon.jpg] https://www.linkedin.com/company/51001/ [https://www.ams.org/images/twitter-icon.jpg] https://twitter.com/amermathsoc [https://www.ams.org/images/youtube-icon.jpg] https://www.youtube.com/user/amermathsoc We appreciate your patience during the Coronavirus Emergency as staff is working remotely.