The value of TabIndex can be from –1 to one less than the number of strings in the Tabs property array (Count – 1). TabIndex is an index to the Tabs array property: A value of 0 indicates the first tab in the tab set control, 1 is the second tab, and so on. If no tabs are selected, TabIndex has a value of –1. 

When a value is assigned to TabIndex, the OnClick event for the tab set occurs, followed by the OnChange event, just as if the user had clicked on a new tab. 

Tabs 

OnChange 

OnClick