That makes it difficult to provide progressive enhancement though. If I use a prefixed property, I have the ability to make sure it works fine without it, and I

That makes it difficult to provide progressive enhancement though. If I use a prefixed property, I have the ability to make sure it works fine without it, and I can assume that in the future, if the semantics of it change when it becomes non-prefixed, it'll either disappear (i.e. if it was a -webkit property being rendered on firefox) or still work (i.e. if it was a -o property being rendered on opera). If I use an experimental non-prefixed property, how do I make sure future browsers that might implement it differently render it usably?