The online help contains the following part at the LaTeX section: "Learn more: MathJax help."
Problem is, the link leads to a site about TeX, not MathJax. This is not really fortunate, as they're not equivalent; a link like this or this would have been much more helpful here. (The reason why I used the word "misleading" is that it literally says "MathJax" help, yet the link leads to a TeX site.)