I’ve noticed that Jekyll replaces $$<whatever>$$ with \[<whatever>\] in my posts.
This can be easily reproduced by creating a completely new blog via jekyll new blog-test and replacing the post content at 2020-10-08-welcome-to-jekyll.markdown by $$aaa$$, keeping the post header.
So 2020-10-08-welcome-to-jekyll.markdown looks like
---
layout: post
title: "Welcome to Jekyll!"
date: 2020-10-08 22:21:11 +0300
categories: jekyll update
---
$$aaa$$
but the generated html contains \[aaa\].
Why does this happen?
It seems like some ‘magic’ for MathJax or similar, but the default blog generated by jekyll new does not use MathJax, and anyway MathJax allows configuration of delimeters, so there is no need to automatically convert $$ to \[/\].
In fact, in my real blog I do use MathJax, and had configured it to use $$ as delimeters, and was using $$ as delimeters. It has been working for about 2 years now, but suddenly it became broken, obviously after jekyll update. Of course, now I’ve updated my MathJax configuration to accept \[/\] as delimeters too, so my specific problem is solved, but still the behavior is very strange and puzzling.
Jekyll 4.1.1, Ubuntu.