[devereaux]

127/8 may only be understandable to those who already know that the whole 127.255.255.255 range is reserved for localhost use.

Sometimes being understandable is more important than using the most precise and shortest notation.

[Fnoord]

127.255.255.255 is a broadcast address in the /8. It doesn't describe the amount of bits in the network. You need a netmask or CIDR notation for that. For IPv6 you need CIDR, so I suggest to learn that.

CIDR is understandable for people who know basic networking. If someone doesn't understand what 127/8 means (which is totally OK if someone doesn't) I'd argue they shouldn't learn about the topic we discuss (valid HTTPS certs for localhost); they should learn something as basic as CIDR first. CIDR isn't difficult to understand. Basics first. You can't learn to speak English if you don't know how to open and close your mouth...