I'm quite ignorant on this all, so correct me if i say errors, but isn't Markdown a text-to-HTML syntax ?

That's what i get from the Wikipedia page, and from both specifications it mentions :

• The original (?) one :

For any markup that is not covered by Markdown’s syntax, you simply use HTML itself. There’s no need to preface it or delimit it to indicate that you’re switching from Markdown to HTML; you just use the tags.

• The CommonMark one :

An HTML block is a group of lines that is treated as raw HTML (and will not be escaped in HTML output).