I think `s/First/Root/` would be better here.

Also, let's just make this return the tag as a number. jsas is already smart enough to turn the tag's numeric value into a string: https://github.com/mozilla-b2g/jsas/blob/master/protocol.js#L576

I'd just implement this as:

```
get rootTag() {
  return this._rootTagValue;
}
```