After recent update, \boldsymbol \partial renders badly in MathJax 3 (tex-chtml)

[MichaelAllenWarner]

Issue Summary

A few weeks ago, \boldsymbol \partial was giving beautiful browser-consistent results in MathJax 3 (tex-chtml), and it looked to be simply the boldface version of the \partial symbol, exactly as expected.

Today, I noticed that it's now giving poor and browser-inconsistent results, and looking at the source code I see that the character is rendered not as the content of a ::before pseudo-element (as is the case with other characters in the equations), but rather as a literal 𝛛 character in a Text node.

Steps to Reproduce:

1. Use the https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml.js component.
2. Use \boldsymbol \partial in an equation.

Technical details:

• MathJax Version: mathjax@3/es5/tex-chtml.js

Supporting information:

• Live link: https://michaelallenwarner.github.io/physics/2019/07/16/vector-triple-products-in-minkowski-spacetime.html#the-double-curl

• Screenshots of inconsistent browser results (Chrome vs. Firefox):
  
  

• MathJax config: https://github.com/MichaelAllenWarner/MichaelAllenWarner.github.io/blob/master/assets/mathjax-prescript.js

• Script tag: https://github.com/MichaelAllenWarner/MichaelAllenWarner.github.io/blob/master/_includes/head.html#L44

[dpvc]

Thanks for the report. This is due to changes in the font handling in order to allow MathML mathvariant attributes to select greek letters better (including upright ones, which are not in the default MathJax fonts). The \partial macro should produce mathvariant="italic" but currently does mathvariant="normal", so when \boldsymbol emboldens it, it gets mathvariant="bold" rather than mathvariant="bold-italic" where the proper character can be found.

A work around for now would be to add

<script>
MathJax = {
  startup: {
    ready() {
      MathJax.startup.defaultReady();
      const font = MathJax.startup.output.font;
      font.getChar('bold', 0x2202)[3].smp = font.getChar('bold-italic', 0x2202)[3].smp;
    }
  }
};
</script>

(or merge it into your current configuration). This will put the bold-italic partial into the bold font for now.

[MichaelAllenWarner]

Like a charm—many thanks.

[dpvc]

Fixed in v3.1 released today.