The point of the
<portal> element (behind a flag in Chrome Canary) is that you can preload another whole page (like
But it's not the web platform at its best when things are done inaccessibly. Steve Faulkner wrote "Short note on the portal element" where he points out seven issues with the portal element as it exists now. Here's a demo of it with some of those issues addressed. I guess it's somewhat of an implementation issue if a lot can be fixed from the outside, but I imagine much of it cannot (e.g. back button behavior, whether the loaded pages becomes part of the accessibility tree, etc.).
Here's a video of the basic behavior: