Well, if you want complex things like nested code blocks, then a kind of "tag" approach can be just the solution needed. Input-wise it doesn't really make a difference, whether I have to type "[[[" and "]]]" or "```" and again "```". Whether or not my idea is more like a tag doesn't seem to have any repercussions. Outsourcing ever more complexity into the parser, with bad design decisions however has a significant cost, which is making development of parsers and grammars difficult.