Carefully audit all uses of "in parallel" in the spec

[bzbarsky]

I'm only partway through respondWith, and there's all sorts of things in there that should not be happening "in parallel", and other parts of this spec have similar issues (e.g hthttps://w3c.github.io/ServiceWorker/v1/#dom-cache-put does mutations on a shared data structure "in parallel"; it's not clear how that's supposed to work exactly).

Please audit all uses of "in parallel" to ensure they actually make sense.

@domenic @wanderview

[jungkees]

It's true that I didn't fully consider that point. After seeing whatwg/html#2774, I thought I should review all the cases indeed.

[monica-ch]

Bug triage: Editors to prioritize