I think another macro, `json!()` works better as an example for that: inside the `json!()` you write something very similar to actual JSON. So when you see a `!` you know that there might be something out-of-the-ordinary following: https://docs.rs/serde_json/latest/serde_json/macro.json.html

Incidentally it also means that formatters like `rustfmt` won't apply the usual rules. For the macros that don't really deviate from ordinary Rust syntax, that can be a bit annoying.