MathJax state: \newcommand and friends, numbered eqs

[cben]

[cben]

Turns out MathJax has stateful support for \newcommand, and it works.
However it depends on the order they're typeset, which might not correspond to document order
To make it usable:

• Leave $\newcommand{...}$ in source form instead of becoming invisible (special case of Dont allow empty formula rendering #10).
• on change to a $\newcommand...$ formula, re-typeset all (or all following) math.

[cben]

• Also pass \[re]newcommand... without any $ etc delimiters to mathjax.
  Pandoc does this.

[cben]

Undocumented: \newcommand alters MathJax.InputJax.TeX.Definitions.macros and MathJax.InputJax.TeX.Definitions.environment. Could try to save/restore them instead of re-typesetting all following math.
However, it's rare enough that re-typesetting should be acceptable.

[cben]

Simular (but worse?) issues of rendering order sensitivity happen with \begin{equation} numbering. See mathjax/MathJax#422.

This is going to be more acute if I optimize initial pass (#14) to be partial/out-of-order.

• Learn which phase of MJ updates state (macros, numbers, labels). Preprocess? Process? Render?

UPDATE: MJ 2.7 added resetEquationNumbers() API https://docs.mathjax.org/en/v2.7/advanced/typeset.html#reset-automatic-equation-numbering, in MJ 3 it's texReset(): https://docs.mathjax.org/en/v3.2/web/typeset.html#resetting-automatic-equation-numbering

[cben]

http://jsfiddle.net/89r6p/3/ demonstates mathjax running again (click) on labels, numbers & refs.

[cben]

Numbering state is in MathJax.Extension["TeX/AMSmath"].number and MathJax.Extension["TeX/AMSmath"].startNumber; there is a host of other variables to handle labels&refs: https://github.com/mathjax/MathJax/blob/master/unpacked/extensions/TeX/AMSmath.js#L562

[cben]

• syntax highlight \begin...\end
• syntax highlight \newcommand...}
• avoid "label foo multiply defined" which makes labels completely unusable

[cben]

• handle \DeclareMathOperator not wrapped in $...$
  • handle any tex macros not wrapped in math? Probably WONTFIX.

Should check how pandoc handles those.