> In fact, a code fence need not consist of exactly three backticks or tildes. Any number of backticks or tildes is allowed, as long as that number is at least three

Unfortunately, some markdown implementations don't handle this well. We were looking at using code-fence like syntax in Rust and we were worried about people knowing how to embed it in markdown code fences but bad implementations was the ultimate deal breaker. We switched to `---` instead, making basic cases look like yaml stream separators which are used for frontmatter.

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bityard 2 hours ago | parent [-]

`---` is already used in Markdown for horizontal rules?

	▲	nicoburns an hour ago \| parent \| next [-]
		The problem here is that if you use ``` as a token in a non-markdown language, then it's going to be very hard to embed that code in a markdown code block. That problem doesn't happen with other syntax as it's already escaped by the code block. `---` inside a markdown code block will render as a literal `---`.
	▲	_ache_ 2 hours ago \| parent \| prev [-]
		Yeap, along with `+++`, `**` and mixing if I remember correctly. I don't understand the logic of using an non-standard syntax because some non-standard implementations may not render correctly. Actually, yes, now you know for a fact that none of the Markdown implementation will render it correctly. So, I guess, they used `~~~` instead and it was an error in OP post.