The current doc is wildly out of touch with reality. A regex search shows
the following stats.
```
Style example Frequency Regex used
nix-2-5: 8 [a-zA-Z]-[0-9]+(-[0-9]+)+ =
nix-2_5: 17 [a-zA-Z]-[0-9]+(_[0-9]+)+ =
nix_2_5: 689 [a-zA-Z]_[0-9]+(_[0-9]+)+ =
nix_2-5: 1 [a-zA-Z]_[0-9]+(-[0-9]+)+ =
```
daca830722