[kbenson]

> Let's look at the grep example agsin. If it did same thing, but new interface, then it would be same thing because behavior is otherwise the same.

That sort of depends on how you define "behavior". More specifically, if it matches something equivalent but different to regular expressions (even if it's just a character transliteration to regular expression syntax), then does the behavior change? Is that still grep? Maybe, if grep decides the the "new grep2 have an easier to learn matching language". It's not like we haven't seen that before.

> I mean, I still think sameness or newness is an open issue.

Sure! The vast majority of cases it probably is an open issue, because different people have different criteria. I was just pointing out that the wording from MS doesn't necessarily imply a rewrite as many people might define it, because we have very little context to go on in the statement, and different people have different ideas about what is the browser. The rendering engine? The UI? The JS VM? All of them combined?

I can totally see someone responsible for the rendering engine saying "we rewrote most of the source code" and the JS VM guys scratching their heads wondering what the hell they are talking about, because they definitely didn't rewrite most their code, and they think their component is a significant portion of the browser...