Have you ever wondered that a Chrome Extension ID is basically something like "pjkljhegncpnkpknbcohdijeoejaedia", a 32 long alphabetic characters identifier that uniquely identify a Chrome Extension.
At the very beginning of Chrome though, this identifier could also contain some numbers. And in some certain cases, it could contain only numbers. Ok... what's the issue here?
As a matter of fact, it turned out that Chrome would consider the full-numeric Chrome Extension ID as an IP address.
Instead of tweaking the net stack, Google Chrome Team decided to use [a-p] encoding instead of [0-9a-f]. That's actually the reason why you won't see any "z" for instance in a Chrome Extension ID.
It also means the number of Chrome Extensions can't be more than 3.4028237e+38 (16^32).