Adding Mathjax Macros to publish.js?

Wondering if/how I can add macros to publish.js so that I can make up for MathJax’s deficiencies. For one:
\iddots $\kern3mu\raise1mu{.}\kern3mu\raise6mu{.}\kern3mu\raise12mu{.}$, the counter-diagonal cousin to \ddots $\ddots$, the typical main-diagonal dots. I know that is not standard latex, so I would like a macro. I have seen this script

<script type="text/x-mathjax-config">
TeX: {
Macros: {
  iddots: "{\\kern3mu\\raise1mu{.}\\kern3mu\\raise6mu{.}\\kern3mu\\raise12mu{.}}"

Is this the correct syntax? Can I add this to publish.js?
(I don’t know anything about how publish.js works because I couldn’t find documentation for it anywhere)