Comment by orthoxerox

> If it cannot render in GitHub it's not real. If it's harder for me to write in the 99% case then it's not worth it. If it's harder for me to implement within my application then I'm too lazy to switch.

There's also on-prem Bitbucket, which supports an even more limited form of Markdown. One could always use CI to render the documentation into Confluence (because it's a safe bet someone who uses Bitbucket uses Confluence as well) using Pandoc, but it's still a downgrade in usability: you can't just review the changes to the documentation done in branch A in rendered form.

But yes, GitHub is king. I don't like mermaid.js, but when I do, I do my diagrams in mermaid.js because GH renders them.