What you're missing is that the value of the string is interpreted as the regex, and not how you write the source code for the string. So a double backslash in the source code is actually just a single backslash in the string, and in the regex; and 4 backslashes in the source code is actually a double backslash in both string and regex.
No, I understood that part. I just thought that you were saying that a string isn't applied like a regex at all -- so it seems that this is what I misinterpreted. Thanks for the explanation.