What are all the `msg_type`s for a JSON download_url response?

I am retrieving a response from the download_url for the JSON file_extension key in the archive_files API endpoint.

That returns a messages array that includes a msg_type key. What are all the possible values for that key? I know they range from 1 to at least 7, but I have not been able to find every possible value and what the values mean.