[icebraining]

No, it's not completely new from scratch:

So we set about to create a new engine using IE11’s standards support as a baseline. I watched Justin Rogers, one of our engineers, press “Enter” on the commit that forked the engine—it took almost 45 minutes just to process it (just committing the changes, not building!).

http://www.smashingmagazine.com/2015/01/26/inside-microsofts...

[manigandham]

At the risk of getting pedantic... they basically deleted the majority of it.

>> In the coming months, swathes of IE legacy were deleted from the new engine. Gone were document modes. Removed was the subsystem responsible for emulating IE8 layout quirks. VBScript eliminated. Remnants like attachEvent, X-UA-Compatible, currentStyle were all purged from the new engine. The codebase looks little like Trident anymore (far more diverged already than even Blink is from WebKit). What remained was a clean slate.

At this point, they kept basic stuff any rendering engine would do but it's as clean a start as you can get.

[icebraining]

A clean engine is Servo. This just sounds like cleaning up the codebase.

[manigandham]

Cleaning up implies they didn't add anything else. This is a major reworking that changes the entire stack.

Do they have to write every single line from scratch again? That would be an enormous waste of time. Even if they started with a completely new repo, they would just copy/paste that stuff anyway. The important bits are all new and that's what matters.

[icebraining]

They don't "have" to do anything, nor am I criticizing them. I'm just saying that's it's not completely from scratch like people are saying. If they take this an some sort of attack, it's their problem.

[chinpokomon]

It's a Ship of Theseus[1]. You can call it a derivative of IE, but that is doing a disservice to what Edge has become.

[1] http://en.m.wikipedia.org/wiki/Ship_of_Theseus