Latex preamble support

[Nambers]

Is your feature request related to a problem? Please describe. Offer a place to list newenvironment and newcommand before all latex block. https://www.overleaf.com/learn/latex/Commands_and_environments https://www.overleaf.com/learn/latex/How_to_Write_a_Thesis_in_LaTeX_(Part_1)%3A_Basic_Structure#The_preamble Basically It like header file of Latex?

Describe the solution you'd like We can list all those newenvironment etc in a file or in config file.

Additional context In Obsidian I can apply community plugin obsidian-latex to enable it. It only took few lines:

...
if (MathJax.tex2chtml == undefined) {
      MathJax.startup.ready = () => {
        MathJax.startup.defaultReady();
        MathJax.tex2chtml(preamble);
      };
    } else {
      MathJax.tex2chtml(preamble);
    }
...

However, I don't think rehype-mathjax support this...