Negative kerning in `\operatorname`

[rudolf-adamkovic]

Issue Summary

Negative kerning does not seem to work inside of the \operatorname.

Steps to Reproduce:

1. Typeset \operatorname{V{\kern-2pt}ar} with MathJax.

Expected: "V" adn "ar" typeset closer together.
Actual: "Missing dimension or its units for \kern" error.

Note: Positive values (e.g. 2pt) work, negative (e.g. -2pt) do not.

Technical details:

• MathJax Version: 3.2.0
• Client OS: macOS 12.1 (21C52)
• Browser: Firefox 96.0.3 (64-bit)

[dpvc]

Yes, MathJax's implementation of \operatorname{} isn't quite as sophisticated as LaTeX's. As I recall, the LaTeX version uses \catcode to adjust the meaning of - so that things like \operatorname{ab-cd} use a text dash for the - rather than a minus sign. MathJax doesn't implement \catcode, and so tries to mimic this behavior by replacing - in the argument of \operatorname by \text{-}. That means in you case that the argument becomes V{\kern\text{-}2pt}ar, which is the source of the error message (since it looks like \kern has no following dimension).

One work around for now would be to use

\newcommand\kernminustwo{\kern-2pt}
\operatorname{V\kernminustwo ar}

though I know that is ugly. I'll see if I can think of a better approach, but it is an edge case, and may not be addressed.

[dpvc]

There is a PR (linked above) that resolves the issue, and it should be in the next release.

[rudolf-adamkovic]

@dpvc Thank you so much!