I'm not talking about a dependency for the file to be readable. I'm talking about a dependency for the diagram to be useful. I'm not opposed to extending markdown, but most functionality like this seems to involve bolting on external dependencies to take advantage of it.

So you want every markdown parser to support building diagrams as well? That seems much more difficult than offloading it to an open source library. Why waste effort that already has gone into building an easy to read diagraming language?

I'm pretty sure stakkur means mermaidjs is a bad option for markdown, as its source form is not "useful" as a diagram, and that it's actually GitHub which is saying every "markdown parser (/renderer) should support building diagrams as well" since they're encouraging its use by supporting the syntax.

The real criticism of the original comment is that markdown has never really been "portable"; yes there's now a hard dependency (for some definition of "hard") on mermaidjs for GitHub-flavored-markdown, but that actually brings it in line with other implementations. So has portability been obviated or just slightly changed?

There's also been other Markdown renderers that support this exact syntax for Mermaid blocks for ages. I have a site that's generated using mkdocs that uses Mermaid diagrams, and I was able to open up one of the files from that site in Github and view the diagrams.