I don't much care about https://github.com/tc39/ecmarkup/pull/694/changes#r3530802437 , but I'd like to resolve it quickly so we can merge the PR and cut an ecmarkup release. So, who would like to weigh in on how setMultipagePreference ought to be wired to #shortcuts-help?

1. in multipage.js, as a listener on document with runtime filtering
2. in multipage.js, as a listener on #shortcuts-help that is dynamically added immediately if that container already exists or otherwise in a DOMContentLoaded callback
3. in Spec.ts, as an inline script element accompanying #shortcuts-help