Syntax and verification of .cursorignore file

Is there some examples and instructions on how to write a valid .cursorignore file?

After re-indexing, how can I verify that the .cursorignore worked?
(this question is a little bit similar in ask to .cursorignore exceptions)

Same syntax as .gitignore! We use ripgrep’s excellent ignore crate (ripgrep/crates/ignore at master · BurntSushi/ripgrep · GitHub).

One way to verify is to try to do an advanced codebase chat request, with the include filter being exactly the ignored files. You should get zero results.