HTML5 open web platform question

[Gizzz]

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/

[yangshun]

I agree. A better answer is welcome. Off the top of my head, and based on the diagram:

I think some components are: HTML, JavaScript, CSS, HTTP, Security, Performance, Accessibility, Web Media (images, audio, video), WebGL, Storage (Cookies, Local/Session Storage, IndexedDB), Service Workers, Performance, Animation, Web Asssembly, Search Engine Optimization, and more. Would be nice to have some further elaboration on each component.

[captainWaheed]

This diagram covers mostly all of the possible blocks.
I just saw this: on https://flowerszhong.github.io/2013/11/20/html-questions.html

[ishratumar]

HTML5 building blocks:

1. Semantic elements such as the header, main, section, footer, etc.
2. Introduced new attributes for the form's tag.
3. The local storage of data that allows webpages to function more efficiently offline.
4. Embedding multimedia is possible without third-party plugins.
5. Canvas that offers a much greater range of presentation options.
6. Document Object Model (DOM) and APIs.
7. Support for mathematical formulas and SVG files.

Reference