[3]
rel=subresource
と直接の関係はありません。
[5] Align Fetch's destination concept with changes in Fetch (sideshowbarker著, ) <https://github.com/whatwg/html/commit/5e8f96a85d182d36c177db0d6fdde58b4ded86d4>
[1] Split up media into video, audio and track (yoavweiss著, ) <https://github.com/whatwg/fetch/commit/ba175cf1100045da83ed0d7768629653aa979c20>