[5] 元々はヘッダー名は大文字混じりとなることがありました。 (細かな動作は実装依存ながら、語頭が大文字となることが多かった。) 現在はヘッダー名はすべて小文字で返すことになっています。
[1] Define get(All)ResponseHeader(s) in terms of Fetch ( (annevk著, )) https://github.com/whatwg/xhr/commit/ecce3904ace0dbe382a652ea1d8e29c7885fe8c4
[4] Sort headers lexicographically in getAllResponseHeaders and combine values too · Issue #50 · whatwg/xhr () https://github.com/whatwg/xhr/issues/50
[2] Align header handling with Fetch (annevk著, ) https://github.com/whatwg/xhr/commit/a6e79810a381b8e336570da797967c4b34e0c6b1
[3] Sort and lowercase header names in getAllResponseHeaders() example (annevk著, ) https://github.com/whatwg/xhr/commit/76b482b68ed9c27e0cc65fd3a6e663999cfc25e4
[7] Change how getAllResponseHeaders() sorts (annevk著, ) https://github.com/whatwg/xhr/commit/985f2f7a6de02dce42e157e02e9bb540d2750edc
[8] Sort headers as if ASCII-uppercased · Issue #248 · whatwg/xhr () https://github.com/whatwg/xhr/issues/248
[9] Change how getAllResponseHeaders() sorts by annevk · Pull Request #249 · whatwg/xhr () https://github.com/whatwg/xhr/pull/249
[11] Change how getAllResponseHeaders() sorts by annevk · Pull Request #249 · whatwg/xhr () https://github.com/whatwg/xhr/pull/249