About [[MathJax:Tex-MissingLeftExtraRight/en]]
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Can we put HTML tag here? For example on hebrew translation lrm [a hidden character] is used in order to make move slash to the right place but I suggest using <span dir="ltr" style="unicode-bidi: embed;"> because we should prevent using lrm/rlm in HTML as far as possible per standards.
Good question. I don't think we thought enough about bidi. I'll raise this on the MathJax end.
For reference: https://github.com/mathjax/MathJax/issues/601