In HTML section there is a question:

Consider HTML5 as an open web platform. What are the building blocks of HTML5?

And the answer is from MDN's HTML5 docs:
https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/HTML5

Probably something different is meant in the original question. I understand it as a question about tech stack of open web platform. Please take a loot at the diagrams on this pages to see what I mean:
http://tess.oconnor.cx/2009/05/what-the-web-platform-is
https://hsivonen.fi/web-stack/