Strange bug with using \tag after \color

[kwankyu]

This is with MathJax version 3.

In the source webpage, after this math display

\[
	\begin{aligned}
	\color{red}{1}
	\end{aligned}
\]

I have this math display

\[\tag{S}
\]

On the rendered webpage, the second display shows a strange error

     \tag is not allowed in aligned environment

This seems a bug in MathJax.

[dpvc]

I can reproduce the result, and yes, it does seem to be a bug. Thanks for the report. I will investigate further.

[dpvc]

OK, I figured it out. The tagging module keeps a stack of tagging information (as different environments are started and stopped), and it turns out that during the autoload of the color extension, the tag information was not being reset when the equation was being re-rendered. That left an extra tagging information object on the stack, and that ended up being the initial state for the next equation (instead of a blank one).

Here is a configuration that I think will fix the issue for you.

MathJax = {
  startup: {
    ready() {
      const {AbstractTags, TagInfo} = MathJax._.input.tex.Tags;
      const clearTag = AbstractTags.prototype.clearTag;
      const startEquation = AbstractTags.prototype.startEquation;
      AbstractTags.prototype.clearTag = function () {
        clearTag.call(this);
        this.currentTag.tagId = '';
      }
      AbstractTags.prototype.startEquation = function (math) {
        this.history = [];
        this.stack = [];
        this.clearTag();
        this.currentTag = new TagInfo('', undefined, undefined);
        startEquation.call(this, math);
      }
      MathJax.startup.defaultReady();
    }
  }
}

I will make a pull request that makes these changes for the next release.

[kwankyu]

Thank you for the fix!