is tabselected necassary?

`tabselected` isn't defined in the registration object in V1.

```
if (fireSelected) xtag.fireEvent(tabbox, 'tabselected', {
  detail: {
    currentTab: tab,
    currentPanel: panel,
    previousTab: previous[0],
    previousPanel: previous[1]
  }
} );
```

I was wondering if you understood this line, and why it was added I think it would have been good if it were completed. 