Microsoft gates plenty of training content behind Visual Studio subscriptions. Also, who is the "provider" of the web platform?

No, we at Microsoft don't make you pay for any of our own developer training material with a VS subscription.

https://visualstudio.microsoft.com/vs/benefits/#training?cat... - you can see that the learning materials you get for subscribing all come from third-party partners, from whom you could buy the same things separately.

WHATWG? The group of browser vendors that agree on web standards. I think the onus is on the person proposing a web technology to document it.

The spec already documents what ought to happen, what you need is documentation about what actually happens (say, on IE11).

I get your point...

The provider of standards around the web is ostensibly the w3c, in reality whatwg or Google. Any of these three would be good candidates to run something like mdn. However that would probably make mdn more political and opinionated.