WIP: FEATURE: custom inline and block math delimiters

[danielhollas]

Per several user requests, this PR adds two new settings for users to specify custom (possibly multiple) math delimiters. Note that users using the old plugin have no good way to upgrade without this functionality.

The new code also handles things like \begin{align}...\end{align}. These must be treated as a special case because they need to be passed to MathJax.

Here's my test code:

Inline math $E=mc^2$  and inline math with custom delimiter `!`  !E=mc^3!

ascii math %E=mc^2%

Default Block Math
$$
E=mc^2
$$

Custom block math with `$$$`
$$$
E=mc^2
$$$

Custom block math starting with `\begin{align}`
\begin{align}
\hat{H}\Psi &= E \Psi \\
\hat{H_i}\Psi_i &= E_i \Psi
\end{align}

And here's how it looks:

---

---

(note that the \begin{align} does what it's supposed to do, i.e. align multiple equations on =)

TODO / TO DISCUSS:

• The current approach does not allow for different delimiters for beginning and end, such as \[ display \]. If we want to support all that's out there, we should allow this. DONE ✔️

• The current code only allows for single-character inline math delimiters (because that's how it was written originally), but one of standard TeX syntax for inline math is \( inline \) so we should allow this.

• Instead of requiring admins to insert every \begin{*}...\end{*} environment they want to support, we could have a switch to process every block math of this form. This would be MathJaX only, KaTeX does not support these, although it might in near future. DONE: ✔️

[ZogStriP]

Was this discussed on https://meta.discourse.org?

[danielhollas]

@ZogStriP here's the latest user comment and here an earlier comment from Sam from the previous discussion on this topic.

At the end of the topic, there's also a separate convo about boundary characters and usage on Chinese forum. Since I will be touching that code anyway, I am inclined to include to do it as part of this PR, but it may be separate.

I am taking this as an exploration for now. This is not yet ready to review, but close. If I get a green light, I'll add lots of tests to cover different use cases.