Capturing mouse position outside of browser window?

Question

One major barrier to creating immersive experiences in the browser (using WebGL and similar) is the set of limitations placed on mouse control.

For instance a first per

Answer 1

That really seems like a far bigger security issue than allowing the developer to reposition the cursor. The answer is no, there's no such thing. And there probably won't ever be one. Sorry!

Update: I was, of course, talking about the capturing outside the window that would be a problem. It's very likely that there will ever be an API that locks the mouse, maybe after asking the user's permission. As nickf pointed out, they're already working on it -https://www.w3.org/TR/pointerlock/

Original defunct link - http://dvcs.w3.org/hg/webevents/raw-file/default/mouse-lock.html