There was a whole team behind Microsoft Trident (IE engine) that was dissolved in favour of third-party (for them) Blink engine. That team was surely knowledgeable, but they had gone.
Blink source is de facto current spec. Each function, if not single line, there is a paragraph in spec.
I remember at WHATWG / HTML5 WG times when Ian Hickson (Google) was pushing whole SQLite (and its SQL flavour) to be included in HTML5 ...
The spec area is so huge and indeed obscure that even Microsoft could not handle it.