addTag after sprint start

Hello,

I would like to set a tag "Unplanned" to every task that is added to a board after the sprint start date.
Something like:

```
if (sprints.added.last.start < now) {
   addTag("Unplanned");
}
```

In some language references I found the start and finish properties on sprint but the Workflow Editor marks it as an error.
I'm using YouTrack 7.0.

Cheers,
Christof