IPv4 addresses as keys

We have a use case for IP addresses as keys, but this runs into a conflict with the Box dotted notation:
```
areas:
0.0.0.1:
kind: stub
```

becomes
```
areas:
0:
0:
0:
1: etc.
```

Would it be possible to add a regular expression for keys excluded from dot expansion?

Start by locating the Box dotted-notation key expansion entry point and trace how the example key 0.0.0.1 is split. Define how a regular-expression exclusion would be configured and verify that matching keys remain intact while other dotted keys still expand; add or run focused tests for both behaviors.

Written by the indexing model from the issue text.