Idea: Allow branches inside multiline conditional to be labelled

(Originally posted by @joningold on our internal Asana.)

As in:

```
{once:
- It was sunny.
- (rainy) It was raining.
}
{ rainy: The ground was wet. }
```

These aren't gather point so it could be this is totally impossible. Certainly, the idea of diverting to a point like this is... a bit weird. But it'd be very useful to be able to test the read count nonetheless..!