The History of the URL: Path, Fragment, Query, and Auth

Re:The History of the URL: Path, Fragment, Query, and Auth by DougBTX on Monday July 18, 2016 @05:53PM (#12118270)

https://www.ietf.org/rfc/rfc1738.txt may shed some light on this. It describes the ":" as the separator, while the // is a scheme-specific prefix, like a super-powered path separator.