What delimiters work for MathJax?

Question

I thought I knew a thing or two about post formatting, but these posts on the two Mathematics sites surprised me: Vector Convolution? (Mathematics SE) and Vector convolution? (MathOverflow). The first equation in those posts uses MathJax but without the familiar $ or $$ (or on selected sites, \$) delimiters; instead MathJax seems to detect \begin{equation} and \end{equation} now. This very old post seems to suggest that didn't work before, but I assume that was an old version of MathJax. Is this behaviour documented somewhere, and are there more delimiters like this?

Answer 1

Here are the delimiters that I confirmed to work on MathOverflow (it will be a bit different on sites that use \$ instead of $). I’m not sure if the list is comprehensive; feel free to fix it if anything is missing or inaccurate:

• Inline math delimiters $ ... $.

  _{^{(Neither \( ... \) nor \\( ... \\) work.)}}

• Display math delimiters $$ ... $$ and \\[ ... \\].

  _{^{(The latter is an escaped version of LaTeX’s \[ ... \].)}}

• LaTeX-style environments \begin{<name>} ... \end{<name>}.

  Here, <name> is any string with balanced braces { ... }; it must be the same in \begin and in \end, otherwise it is not recognized as a delimiter. _{^{(Improperly nested environments such as \begin{equation} ... \begin{align} ... \end{equation} are recognized as MathJax delimiters, but lead to MathJax error messages.)}}

  MathJax predefines common equation environments such as equation, align, or matrix; moreover, it supports user-defined environments using the \newenvironment command. The \begin{<name>} ... \end{<name>} structure is in any case recognized as a MathJax delimiter even if environment <name> does not exist, or if it is invalid as an environment name (e.g., if it includes unexpandable control sequences), however such cases lead to MathJax error messages.

  _{^{For single-letter environment names, \begin X and \end X are not recognized as MathJax delimiters, even though they work fine inside already-recognized MathJax expressions (just like in actual LaTeX).}}

  _{^{Unlike LaTeX, MathJax allows equation environments to be enclosed in other delimiters, such as $$\begin{align} ... \end{align}$$. The outer delimiters are redundant.}}

  _{^{Fun fact: both MathJax and LaTeX allow defining an environment with empty name with \newenvironment{}{X}{Y}. This redefines the \end command, wreaking havoc left and right; it appears that in LaTeX, \newenvironment{<name>} only checks for the existence of \<name>, but not for \end<name>, and happily redefines it if it exists. Sounds like a bug, if you ask me.}}