The index at which the tab was inserted.
An integer in the range [0, <tab count>-1].
String that uniquely identifies the current tabset.
Identifies the window that is the source of the current event.
See the documentation for individual events for more details.
The properties of the newly-added tab.
These will be generated from the tabID window, or will be whatever properties were previously set for the tabID window using
updateTabProperties.
Details of the 'join-tab-group' event