Cannot link to "rules for choosing a navigable"

The [HTML](https://html.spec.whatwg.org/multipage) spec defines [rules for choosing a navigable](https://html.spec.whatwg.org/multipage/document-sequences.html#the-rules-for-choosing-a-navigable), mentioned by the tabbed mode navigation algorithm. However, it is not exported, so it is unable to be properly linked, and may be considered a layering violation to use it.