Hexadecimal ints not handled?

```
MatchFull("0x1234", "(0x[[:xdigit:]]+)", &x);
```

Works when `x` is a string but not when `x` is an `int`.  Is there a way to enable different bases in integer conversion?

I suppose in some fantasy world the base of the integer string could be deduced from the characters allowed to match, but I wouldn't advocate for that.