First discussed at https://answers.netlify.com/t/changes-to-redirects-with-query-string-parameters-are-coming/23436.

/urldemo id=:id /urldemo?redir 301!

Navigating to /urldemo?id=1 will succeed – and use the dummy query string in the to rule.

/urltest id=:id /urldemo?redir

Navigating to /urltest?id=1 will succeed – without the force (!) as /urltest doesn't exist – and use the dummy query string in the to rule.