According to MDN, HTML “is the most basic building block of a webpage”. It’s the foundation of the web. The first webpage was built on less than 75 lines of HTML. Yet for such a fundamental part of the web, I find that many front-end developers don’t have a good handle on it.
Editors, templates, and frameworks produce HTML that enable a developer to get content on the page but the resulting code often lacks the features and nuances of the language such as semantics to convey meaning and enhance SEO or attributes and meta data to improve accessibility.
If you’d like to learn more about HTML, I find that the MDN docs are a great starting point. You can also hit me up on Twitter as I love talking about this sort of thing.