- We recently hit an issue where we expected the MathJax extension to
work with the default MathJax markup. Obviously that shouldn't be
the case (since then other formats couldn't use the math), but it
can't hurt to include a hint.
- Link from the math HTML extension page to the relevant
roles/directives.
- Also make it explicit that MathJax has a default, and that it's an
external resource that will be dynamically linked.