Confusion over html being case sensitive or not

Question

I googled it and top 2 answers contradict themselves, any help? Thank you

Answer 1

it was though in xhtml, its no longer the case (no pun intended) in html5.
at some part i think an attribute like value of id, class are case-sensitive

Answer 2

Jdub html is not case sensitive.
DOCTYPE HTML or DOCTYPE html or doctype html is the same thing.

Answer 3

Html is not case sensitive but javascript is. We can write HTML as well as html also.

DOCTYPE and doctype are sams in Html.

Answer 4

Element and attribute names are ASCII case-insensitive in HTML.

(https://html.spec.whatwg.org/multipage/semantics-other.html#case-sensitivity-of-selectors)