Validator rules question

Hi!

Wanted to ask, I saw there's a validator rule for mime types, that you provide file extensions too, how does it work?

Does it check just if the mime type matches? Or if the file extension is also matching the mime type of the file? I mean, for example I want to strictly allow only .doc files, and .png files, and a user uploads a file called 'file.doc', that has a mime type of a doc file, would it let it pass or block it?

Cheers.