For issues like MDL-78662, it would be useful to reliably know in JavaScript when something (e.g. maths filter) has finished doing things that change the layout of the page.

In the case of MathJax, there are specific MathJax things you can use to get notified when it has finished rendering and equation, but other bits of Moodle should not really use that. Instead, we should have a generic event (suggested name core_filters/contentRenderingDone), then filter_mathjaxloader can deal with MathJax, and then fire the Moodle event.

This is similar to, but the opposite of, the existing event core_filters/contentUpdated, wihc other code uses when it has added some new content to the page, which filters like filter_mathjaxloader or filter_glossary might need to process.

In the MathJax example, I am thinking we would fire this event once for each equation rendered, an trigger it on that HTML element.