The concepts of internal DSLs and external DSLs is relevant here. The article is an internal, to Python, DSL. It runs in the language the tool is written in. Mermaid is an external DSL. You can’t build a Mermaid renderer in Mermaid. For diagrams I’d rather have an external DSL or a macro system than an internal DSL because it looks cleaner IMO. But it’s nice to have syntax highlighting already working in internal DSLs.