Re-do radicals setup

[wspr]

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Description

Radicals are currently set up with:

\tl_set:Nn \l_@@_radicals_tl {\sqrt \longdivision}

This should be done explicitly in unicode-math-table.tex instead.

Check/indicate

• [x] Relevant for XeTeX
• [x] Relevant for LuaTeX
• [x] Issue tracker has been searched for similar issues?
• [x] Links to <tex.stackexchange.com> discussion if appropriate: https://tex.stackexchange.com/a/438180/1090

Minimal example demonstrating the issue

Doesn't work:

\documentclass{article}
\usepackage{unicode-math}
\ExplSyntaxOn
\tl_set:Nn \l__um_radicals_tl {\sqrt\longdivision\cuberoot}
\ExplSyntaxOff
\setmathfont{xits-math.otf}
\begin{document}

Further details

[eg9]

I see that \sqrt, \cuberoot, \fourthroot and \longdivision are marked as \mathopen in unicode-math-tables.tex.

I think that a class marker such as \mathradical should be used (analogously to \mathalpha, \mathfence, \mathaccent, \mathaccentwide and similar new markers).

[wspr]

Exactly my line of thinking :)

Originally unicode-math-table.tex was fairly limited, and the radical code was written very long ago. When I started adding to the "math classes" I never got around to doing the same for the radicals (largely because they're such a small set).

[khaledhosny]

While at it, it would be nice to handle the Arabic versions of \cuberoot and \fourthroot as well: U+0606 ARABIC-INDIC CUBE ROOT ؆ U+0607 ARABIC-INDIC FOURTH ROOT ؇