Earlier quoted context omitted.
While on the subject, what is the difference between file:/path/to/file and file:///path/to/file ? Usually I only see the latter being used.
In file:///, the file:// part signifies the protocol (think http:// ) and the / in /path/to/file signifies the root directory (think / in /home/user/) I have never seen file:/ used before, so I can't really comment, but it seems invalid to me (and browsers auto-redirect it to ///).
The file: signifies the protocol. The /// is actually /// with an empty machinename as a shorthand for 'localhost'.