In https://github.com/WICG/nav-speculation/ we're working on specifying prerendering. (Latest spec work, integrated with the recent changes to HTML's navigation algorithm, at WICG/nav-speculation#207 .)

The tricky thing about prerendering is there are two "navigation"-type events:

• The hidden, off-screen navigation of the prerendered navigable
• The actual activation, which moves the prerendered browsing context from the prerendered navigable to the user-visible navigable

On the spec level, the latter is done by hooking into the navigate algorithm, and instead of doing most of the normal stuff, instead activating.

HTML's navigate algorithm currently has a variety of WebDriver BiDi callbacks based on a given navigation ID. Should we have any for prerendering activation?