[dom] Make Attr a Node again (#102)

Attr's child text nodes have been successfully [removed](https://groups.google.com/a/chromium.org/d/msg/blink-dev/4Hg0l42QHH0/H59LyoiJlI4J) in Blink recently, aligning with Gecko and the spec on this point. The big remaining difference is that Attr is not a Node in the spec, and this is a change no browser engine (except Servo) has made yet. I doubt that it's really worth it for the web platform to divorce Attr from Node.

First and foremost, it's not clear that successfully making the change would be of much value. DocumentType is already a weird kind of Node, so any algorithms dealing with nodes already have to deal with a similar case. In implementations, this is a sunk cost.

A practical issue is that it's hard to measure the risk, as every attribute and method that Attr inherits from Node and EventTarget is a potential problem. Even if that were done, the fact that `instanceof Node` no longer holds true is a risk that cannot be measured.

Are any implementors interested in attempting the change, and if so when?

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/102