JSON and CSS are supported today, and I'm interested in adding more structured text formats.

If a format has a tree-sitter parser, it can be added to difftastic. The TOML tree-sitter parser looks good, but there isn't a mature markdown parser for tree-sitter. There are other markdown parsers available, so in principle difftastic could support markdown that way.

The display logic might need a little tuning for prose-heavy formats like markdown though. I'm not happy with how difftastic handles block comments yet either.

I'm not sure about formats that contain more prose, such as markdown or HTML.