Markdown and HTML tags including dollar signs

[williamstein]

This gets mangled by the markdown processing:

<a href="http://abc" class="foo-$">test $</a>

The reason is because smc-util/mathjax-utils.js is NOT a full parser, but just some heuristics, and it gets this wrong. It replaces

<a href="http://abc" class="foo-$">test $</a>```
by 

<a href="http://abc" class="foo-@@0@@

then runs the normal markdown processor, then puts `$">test $` back.

Note that exactly this is ALSO broken in Jupyter Classic, which uses the same heuristics rather than a real parser.

[williamstein]

Workaround: this works:

<a href="http://abc" class="foo-$">test \$</a>

[williamstein]

See also #2863

[williamstein]

I just checked, and this has been fixed in cocalc for years now, as illustrated here: https://cocalc.com/wstein/support/issue-2853

I fixed this long ago by switching to using an actual markdown-it math parser plugin (which I rewrote quite a bit to be as compatible with jupyter-classic as is reasonable).