v4 rendering error with double braces around align command like \begin{array}{{cc}}

[SDineenAtOptica]

Issue Summary

Alignment commands in an array or similar produce an error when the alignment command is in double braces such as {{cc}}. This rendering problem did not occur in MJ 3 and does not with TeXLive. Also, the tagging approach is quite common in our library of articles going back decades: \begin{array}{{cc}}

Steps to Reproduce:

1. With a MathJax 4.1 setup for LaTeX, observe the rendering of this equation with and without the double braces around the alignment preamble:

\left( \begin{array}{{cc}}
		a & b \\
		c & d
  \end{array} \right)

2. Observe the error message when double braces like in the example are used:
   Illegal pream-token ({)

Technical details:

• MathJax Version: 4.1.2
• Client OS: Windows 11
• Browser: Chrome 148.0.7778.179

[dpvc]

I have never seen this usage before, so it wasn't something that I realized was a possibility. I will make a PR to fix the problem

In the meantime, one work around would be to incorporate

MathJax = {
  startup: {
    ready() {
      MathJax.startup.defaultReady();
      const {columnHandler} = MathJax.startup.document.inputJax.tex.parseOptions.columnParser;
      columnHandler['{'] = () => {};
      columnHandler['}'] = () => {};
    }
  }
};

into your MathJax configuration. That will cause { and } to be ignored in the preamble. I think that should do what you need.

[SDineenAtOptica]

Thanks for the fast response to this and for the code to help accommodate the coding pattern. Scott