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HTML is a subset of Markdown. You can include in Markdown any and all HTML. What Markdown provides here is an even lower barrier to entry for the majority of people... they just write text, learn a fraction more Markdown to so more... and if they want total control they eventually learn HTML too. It's not mutually exclusive... Markdown includes HTML.
—I’d say it’s the other way around isn’t it? Wouldn’t Markdown be a subset of HTML, since all markdown can be expressed in HTML but not all HTML can be expressed in Markdown?— Edit: Markdown can contain HTML that gets meaningfully interpreted as markup as well. I’d also say HTML is not difficult to write, even for someone new to the concept. I don’t think anyone making their GeoCities homepage was too strained learni…
HTML can’t contain Markdown at all - a ### in HTML does nothing but a hello in Markdown does exactly what you expect it to.