[chrismorgan]

The tricky thing is getting the triangle’s node to be the position of the cursor; you need it to start at the left of the menu item, then animate rightwards only while the cursor is hovering over it, stopping when it’s not—so that it will naturally come to rest. This is possible to express with animations (animation-play-state is key), except for the fact that :hover calculations are not done constantly in most browsers, but only when the user does something to trigger it, such as moving the cursor. And so basically the whole scheme falls apart: it will work just barely OK, but if you move your mouse just a bit too slowly, it’ll effectively stop working.

It’s still an interesting thought. If you’re interested and my explanation isn’t clear enough, I’ll put a simple proof-of-concept-and-why-it’s-sadly-not-really-enough together.

(OK, since then I’ve come up with an insane approach that relies upon this behaviour, and it might just work, though I’m concerned about how reliable it’ll be across browsers. If it does work, it will definitely be blog-post worthy.)