Math uses a Node service; now that we don't need Parsoid/JS, I'd like to avoid setting up Node. We don't have any STEM-oriented spore currently, and by the time we do, Math will be hopefully migrated to pure PHP.

$wgDefaultUserOptions['math'] = 'mathml';
$wgMathFullRestbaseURL = 'https://en.wikipedia.org/api/rest_';
$wgMathMathMLUrl = 'https://mathoid-beta.wmflabs.org/';

So it just uses Wikipedia's rendering service.

That sounds nice. Why does it need two different service URLs though?