> Pages that don't conform with the specification won't be rendered.

I agree on what I wrote here. They will fail with an error indicating where the mistake is so you can correct it (more likely the tool that produced it).

>> The objective is to enforce tools that make the transformation to produce a strictly conformant document. > >Ah, an open and non-monopolizable format which can only be written via an official toolchain.

??

The objective is that when you make a tool like markdown-to-foo, the output follows the spec. There is no mention of any "official toolchain".

> xmlstarlet

XML is strict. Try to find the same tool for HTML5, especially for transformations.

> JSON is an interchange format between machines.

Is pretty much what the specification would try to cover.