[zaphar]

This is sort of correct on webkits side. inheritance chains especially when you don't control who is inheriting from you are going to be very brittle. The standard would probably have been better if it had been specified as a form of composition instead. However not supporting something like this is largely worse than just doing the inheritance. I'm not sure this is a hill I would die on despite largely agreeing with the webkit folks here philosophically.

[chuckadams]

That's my take on it too. The DOM itself is full of issues from its naive inheritance-happy OO design, and could use a refresh into something with better separation between data and presentation, but it's what we have right now in the real world. There's always going to be footguns, we can't put safeties on all of them. I have to wonder if it's something in the design of WebKit that makes inheritance particularly difficult to implement.

As for potential property collisions, I think the common wisdom is to just ensure the property name contains a dash, since the html5 spec goes out of its way to avoid using them. Doesn't solve brittle inheritance hierarchies in general, but it does at least stay out of the way of built-in behavior.