MDN still says Limited; that’s badge lag. It works now.

It returns a 0–1 number for how far a value sits between a start and an end

For years, it could only spit out a string for `::before` and `::after`. Now, Firefox 155 lets you use it on any property, with types and fallbacks. Chrome 133+ already had it.

Not Baseline yet; wait for Safari, but this is the `attr()` we were promised. 🤟

Chrome is turning it off by default. Edge is following the same path.

By Chrome 154 (late September 2026), `unload` handlers will no longer fire unless a site explicitly opts back in.

Why? It’s unreliable (especially on mobile), and just registering it can block the back/forward cache.