It’s not just “extended” flavours of Markdown that allow embedding HTML. The original reference implementation supports this too.[0]
> 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.
> 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.
[0] https://daringfireball.net/projects/markdown/syntax#html