Sure but there's no markdown spec. Markdown is purely a series of blog posts by John Gruber and a collection of different implementations. CommonMark is as close to as it's gotten to a formal spec, and even it says there is no requirement the info string (i.e. text like mermaid after backticks) be interpreted for specific rendering (or not rendering) of the content: https://spec.commonmark.org/0.28/#fenced-code-blocks