Missing spacing for \bmod in subscripts

[int-y1]

Issue Summary

I discovered this issue while working with MathJax 3.2.0. This issue is the same as #794, but the solution was specific to MathJax 2.

Steps to Reproduce:

1. Go to https://www.mathjax.org/#demo
2. Type in AA $i \bmod N$ AA $c_i = c_{i \bmod N}$ AA.
3. 

In the subscript, there should be spaces around the bmod.

Technical details:

• MathJax Version: 3.2.0
• Client OS: Windows 10 21H1
• Browser: Chrome 96.0.4664.45

[dpvc]

Thanks for the report. This is due to the fact that MathJax makes \bmod into a "math operator" as <mo>mod</mo> in MathML, and that will normally get spacing around it, but spacing around operators is removed in script and script-script modes, so that space is lost in the subscript in your example. I will look into resolving the issue.

[dpvc]

OK, it turns out that the lspace and rspace attributes were being given explicitly, as in the v2 solution, but that these spaces were being removed at a later stage by a filter that removes attributes when they equal the defaults. That means the space was not added in the scripts, since the explicit lspace and rspace were no longer there to force the spacing (only the default space, which is removed in scripts).

I've made a pull request (listed above) to resolve the issue.