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<p>I recently filed a bug report on the XeTeX repo about the kerning of sub- and superscripts in OpenType fonts:<br>
<br>
    https://sourceforge.net/p/xetex/bugs/175/<br>
<br>
luaTeX's find_math_kern() has many of the same flaws.<br>
<br>
Cheers,<br>
David.<br>
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P.S. I don't think the related bug<br>
<br>
    https://sourceforge.net/p/xetex/bugs/173/<br>
<br>
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.<br>
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<strong>David Jones</strong><br>
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<i>Publications Technical Specialist</i> <br>
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